Saturday, February 1, 2014

Diagnostic Approach to Pneumonias




Ravindran C, MD*, Jyothi E, MD**









*   Professor of Pulmonary Medicine & Dean, Govt. Medical College, Kozhikode, Kerala
    
  ** Assistant Professor
Dept. of Pulmonary Medicine, Govt. Medical College, Kozhikode, Kerala
       drjyothie@yahoo.com  







Abstract

Pneumonia is always diagnosed on the basis of signs and symptoms, supported by demonstrable radiographic infiltrate. But certain situations warrant an etiological diagnosis which is mostly by microbiological intervention. However these tests are not always helpful especially when the patient was put on an initial antibiotic therapy or when atypical organisms or rarer organisms cause the pneumonia. Common tests are not routinely used due to low yield as well as infrequent positive impact on management decisions. Even though there is disagreement among experts about the composition of the diagnostic investigations for pneumonia; a well-chosen evaluation can support a diagnosis of pneumonia and identify a pathogen. Microbiological diagnosis is also important for epidemiological purposes. Without the accumulated information available from these culture results, empirical antibiotic recommendations are less likely to be accurate. Newer culture methods and molecular technique has been evolved which offers specific diagnosis that too in a shorter time frame. A well-chosen, individually tailored evaluation can offer a lot of information to support the diagnosis of pneumonia.
Keywords: Pneumonia, Chest imaging, Molecular techniques, High resolution CT, Ultrasonography

Introduction

Pneumonia is always diagnosed on the basis of suggestive signs and symptoms, supported by demonstrable radiographic infiltrate. Routine diagnostic tests to identify an etiologic diagnosis are optional for outpatients with community acquired pneumonia (CAP). In many cases of mild-to-moderate CAP, the physician is able to diagnose and treat pneumonia based solely on a medical history and physical examination. The patient's history is an important part of making a pneumonia diagnosis. Patient’s history should include the report on smoking, alcohol or drug abuse, exposure to occupational risks, recent travel and exposure to people with infections including tuberculosis. Physical signs on examination such as impaired note, abnormal breath sound, crackle or pleural rub and findings of pleural effusion are all indicative of pneumonia.

Microbiological data is not always sought for the initial diagnosis of pneumonia. There is disagreement among experts about the composition of the diagnostic investigations for pneumonia, but a well-chosen evaluation can support a diagnosis of pneumonia and identify a pathogen. The yield from routine use of common investigations like blood and sputum culture is usually low and a positive impact on the treatment of the patient is unlikely. But culture reports can have major impact in the treatment of individual patient. Microbiological diagnosis is also important for epidemiological purposes. Along with antibiotic susceptibility pattern, etiologic diagnosis is useful for developing treatment guidelines. The present pneumonia guidelines are based on culture results and sensitivity patterns from various studies. Without the accumulated information available from these culture results, empirical antibiotic recommendations are less likely to be accurate.
The most clear-cut indication for extensive diagnostic testing is in the critically ill CAP patient. In hospitalized patients, it is difficult to diagnose pneumonia, as the patients may be having similar symptoms including fever and abnormal X-rays. Moreover the sputum and blood culture from these patients may grow organisms, which may not be the causative agent for pneumonia. Diagnosis becomes all the more difficult in pneumonia due to atypical organisms, rare organisms and new and emerging pathogens. These situations warrant newer methods of diagnosis such as serology and molecular techniques.
The general recommendation1 is to encourage diagnostic testing in situations where the result is likely to change management decisions and when the diagnostic yield is thought to be greatest. Because of much emphasis on clinical data, a variety of diagnostic tests that may be accurate but the results of which are not available within a time frame are not recommended.
This article reviews various investigations in the diagnostic work up of pneumonia giving special attention to include newer techniques like molecular methods.

Microbiological diagnosis of Pneumonia.

The role of microbiologic studies in determining the etiology of pneumonia is questionable because of the lack of rapid, accurate, easy and cost-effective methods which can be obtained before starting treatment. Even in randomized controlled trials, the cause of community acquired pneumonia is determined in only 20- 40% of cases2. But in a study by Johansson N et al, the microbial etiology of community acquired pneumonia  could be identified in up to 67% of the patients by combining PCR based and conventional methods3. Careful correlation of culture and smear result with clinical and radiological finding is important in arriving at an etiological diagnosis of pneumonia (Table-1).

Pneumonia

Common Organisms

Community Acquired Pneumonia

S.pneumoniae, H.influenzae, M.catarrhalis, M.pneumoniae, Respiratory Viruses.

Hospital acquired Pneumonia

Early HAP: S.pneumoniae, H.influenzae, Methicillin susceptible S.aureus. (MSSA), Antibiotic sensitive enteric gram negative bacilli.

Late HAP: MRSA, P.aeruginosa, Klebsiella pneumoniae,  Acinetobacter species, Legionella pneumophila.

Ventilator Associated Pneumonia

Early VAP: S.pneumoniae, H.influenzae, S.aureus(MSSA)

Late VAP: P.aeruginosa, Enterobacter species, Acinetobacter species, MRSA

Pneumonia in the Immunocompromised.

M.tuberculosis, P.jiroveci, Toxoplasma gondii, Nocardia sp.,Cytomegalovirus,Aspergillus fumigatus .

Table-1: Etiological agents causing pneumonia


The expectorated sputum is the least invasive but the most contaminated specimen. The quality of expectorated or induced sputum is important for obtaining a positive gram stain or culture report. To get a good sputum specimen for culture the patient should be instructed to breathe deeply and cough from deep down in the lungs. Mouth should be rinsed with water before obtaining the specimen to reduce oral contamination. Ideally the sputum sample should be collected before the patient is started on empiric antibiotics.
The initial cytologic examination provides the quality of the sputum and its suitability for culture. The presence of numerous polymorphonuclear leucocytes (>25) and the number of squamous cells less than 10 per low power magnification field is indicative of a good specimen for bacteriologic evaluation.4 The presence of numerous squamous cells indicates that the specimen is derived from upper respiratory tract.
The other specimens from the lower respiratory tract include tracheal aspirate, bronchial washings, bronchioalveolar lavage, protected specimen brush samples, bronchial biopsy, trans-tracheal aspirate, lung aspirates and lung biopsy specimens.
 Another important non-invasive method to retrieve specimen for obtaining microbiological diagnosis is induced sputum. Sputum induction is done by giving nebulization with hypertonic saline, after proper hydration of the patient. The earliest studies on induced sputum were in the cytologic diagnosis of lung cancer and the diagnosis of pulmonary tuberculosis5. The role of induced sputum at present is mainly for microbiological diagnosis in patients unable to spontaneously produce sputum, especially children and immunosupressed patients with pneumocystis jiroveci pneumonia6. In a study by Lahti E, involving 101 children, aged 6 months to 15 years,  good quality sputum specimen was obtained in 76 children and a positive result was obtained in 90% of specimens7.

Gram Staining
Gram staining originally devised by Hans Christian Gram more than a century ago, is the standard method used for identifying micro-organisms even today.8 The commonly seen organisms in gram stained smears include Streptococcus pneumoniae (gram positive oval or lancet shaped diplococci), Haemophilus influenzae (small pleomorphic gram negative bacilli) and Moraxella catarrhalis (gram negative diplococci).9 In nosocomial pneumonia, the infection is usually polymicrobial,  and Staphylococcus aureus, Pseudomonas aeroginosa, Enterobacter species and Klebsiella pneumonia are the commonly identified organisms.
.
Acid Fast Staining
Examination of stained smear for acid fast bacilli (AFB) is the most rapid and inexpensive method for detecting Mycobacterium tuberculosis. The bacteriological examination of expectorated sputum for AFB should be done in all patients with pneumonia especially in developing countries. M.tuberculosis is typically a slightly curved or straight rod shaped microbe. (Fig-1) It is 1-4mm in length and 0.3-0.6mm in diameter9. M. tuberculosis can be stained with carbol fuchsin (Ziehl Neelsen or Kinyoun) and fluorochrome (Auramine Rhodamine) stains. Recently most of the modern laboratories use the fluorochrome staining method. In this staining method mycobacteria appear as bright yellow rods against an inky black background. This is much easier to perceive than the red- blue contrast of Ziehl- Neelsen staining. Auramine Rhodamine staining is more sensitive than ZN staining, especially in paucibacillary cases 10 and the specificity is similar11.

Special staining
Even though gram staining and traditional culture methods are used routinely for the microbiological diagnosis of pneumonia, special staining methods are essential for the isolation of organisms in varying clinical situations.KOH preparation of sputum for elastin fibres is a sensitive test for the diagnosis of necrotising pneumonia12. In intubated patients also, the presence of elastin fibres in KOH added bronchial washings is diagnostic of necrotizing pulmonary infection13. KOH preparation is also useful for identifying fungi in respiratory specimens. The KOH will clear the cellular debris and will make the fungal hyphae and spores more apparent.
Calcofluor white is a nonspecific fluorochrome stain that binds to fungi and Pneumocystis jiroveci.14 Fungal and parasitic organisms appear fluorescent bright green or blue. Initially it was used for staining fungal hyphae, but now it used as a rapid and inexpensive stain to detect P. jiroveci. The sensitivity for diagnosing P.jiroveci in expectorated sputum is less compared to bronchial washings and other invasive specimens.15
Modified Grocott Gomori methenamine silver stain is used for staining Pneumocystis jiroveci cysts and Giemsa staining is used to stain the trophozoites. Pneumocystis is rarely detected in expectorated sputum. Either induced sputum or bronchial lavage specimens are required to diagnose Pneumocystis jiroveci infection.
 Sputum Direct fluorescent antibody is a rapid method for the diagnosis of respiratory pathogens. Prior to the advent of PCR, DFA test was considered as a rapid diagnostic method for Bordetella and Legionella infections. The sensitivity of DFA for Legionnairs disease is less compared to PCR and culture.  So DFA testing for Legionella is not routinely done for diagnosis as highly sensitive tests like PCR and Legionella urinary antigens are available. Direct fluorescent antibody test requires substantial expertise for interpretation of results. DFA tests for P. Jiroveci are also available. In a study by Metersky ML et al it was found that there was no much difference between expectorated and induced sputum when DFA was used for the diagnosis of PJP.16

Culture Methods
Traditional culture methods for microbiological diagnosis are slow, the sensitivity is low and the result may be influenced by prior antibiotic therapy. So it is not possible to treat pneumonia based on culture results.  Over the past several decades, empiric broad spectrum antibiotics are the accepted clinical practice in treating pneumonia. But it is recommended that before starting the patient on empiric therapy a sputum sample should be sent for culture and sensitivity. In a study by Rello et al, positive microbiological test resulted in treatment modification in 41.6% of patients including 5% of patients in whom the initial antimicrobials were ineffective against the isolated organism.17 Another advantage of obtaining a positive microbiology diagnosis is to convert the broad spectrum to narrow spectrum therapy. De-escalation of therapy will help in controlling antibiotic prescription, minimizes the emergence of drug resistance and reduces the treatment cost18
Traditionally sputum culture is done on the following media- blood agar, chocolate agar and MacConkey agar. After assessing the quality of sputum after initial cytologic examination a purulent portion of the sputum sample should be inoculated into culture plates. When there is a significant growth of organism, sensitivity tests should also be done. Specialized culture media are required for atypical organisms like Legionella and Mycoplasma. Legionella grows on buffered charcoal yeast extract (BCYE). Incubation up to 10 days is required for the isolation of the organism and hence culture for Legionella is not done routinely. If fungal infection is suspected sputum should be cultured on Sabaraud’s agar.
For the detection of Mycobacterium tuberculosis both conventional and rapid culture methods are available. Conventional culture media like Lowenstein- Jensen medium will require up to 6 weeks for obtaining a positive culture. (Fig-2) The available rapid culture methods for M.tuberculosis are BACTEC culture medium, Mycobacterial Growth Indicator Tube (MGIT), Septi check AFB and MB/Bact system. These methods will take 1-2 weeks for a positive culture  report.
Until now bacterial etiology was considered in most patients with pneumonia, but in recent years respiratory virus has been recognized as an important cause of pneumonia.3 Tissue culture was the gold standard for the diagnosis of viral pneumonia, but not routinely done now for diagnosis of viral pneumonia, because of the significant advancement of various rapid diagnostic methods.
Blood culture
 Blood cultures are used to identify the organism that caused pneumonia and guide the treatment. Guidelines from the Infectious Disease Society of America and the American Thoracic Society recommend two blood culture samples for all patients admitted to the hospital with pneumonia. The overall yield of blood culture is below 20%. In a study by Campbell SG et al the rate of modification of treatment based on blood culture reports was only 1.97%19. In another recent study by Abe T et al, a positive blood culture was obtained in 3.7% and resulted in change of antibiotics in only 2.4%20. In a study by Waterer GW et al, the yield of positive blood culture increased with pneumonia severity index (PSI) grade, increasing to 26.7% in PSI grade V and resulted in a change in antibiotic treatment in 20.0% of patients with grade V21. So to reduce expenditure and to preserve resources it is recommended to restrict blood culture to high risk patients.

Urinary Antigen
Immunochromatogrphic tests that detect pneumococcal and legionella antigen in urine is a significant advancement in the diagnosis of these 2 pathogens. The advantage of this test is that, the results are not modified by prior antibiotic treatment. It is a rapid and non invasive test for early diagnosis of etiologic agent. Studies in adults have shown a sensitivity of 70% and specificity of 89.7% for the diagnosis of pneumococcal pneumonia22. But in children, sensitivity and specificity is less in a study by Dominguez  et al23. The disadvantage of urinary antigen is the cost and the lack of an organism for drug susceptibility testing. The test will be positive for several weeks to months after the illness.  In a study by Smith MD et al in adults with community acquired pneumonia, comparing PCR with urinary antigen for the diagnosis of Streptococcal pneumoniae, it was found that urinary antigen test was positive in 51 of 58 bacteremic cases whereas PCR was positive only in 31 cases24. In 77 patients with nonbacteremic pneumonia, urinary antigen was detected in 21(27%) patients compared to a positive PCR in 6 (8%) patients.
Legionella urinary antigen is 76% sensitive and > 90% specific for infections caused by Legionella pneumophila serogroup-125.( Table- 2) The major advantage is the rapidity of the test compared to culture, direct fluorescent antibody and serology. Legionella urinary antigen detection is not recommended as a routine investigation for hospitalized patients with community acquired pneumonia, as narrowing antibiotics spectrum based on the results has a higher risk of clinical relapse.26

Organism
Sensitivity%
Specificity%
S Pneumoniae
0-58
>90
Legionella pneumophilia-Serogroup-1
76
>90
                                   Table- 2: Urinary Antigen detection for CAP25
Nucleic Acid Amplification Tests
The development of nucleic acid amplification tests is a major development providing an etiologic diagnosis in respiratory infections. These investigations help in rapid and efficient identification of etiologic agents in pneumonia. It may eventually help in pathogen directed therapy at the time of starting initial antibiotics.
Polymerase Chain Reaction (PCR) detects microbial nucleic acid from cultured sample or direct respiratory specimens. DNA extraction is done from the respiratory sample and the target gene is amplified.  There will be exponential amplification of target gene. These are then identified by gel electrophoresis and DNA sequencing.
The major advancement in PCR has been the multiplex PCR. It is a variant of PCR which enables simultaneous amplification of many targets in one reaction by using more than one pair of primers, so that multiple respiratory pathogens can be identified in a single test27. It was first described by Chamberlain in 1988. In a study by Templeton et al , on 358 respiratory samples over one year period, respiratory virus were detected by viral  culture in 67 (19%) samples and by multiplex PCR in 87 (24%) samples showing that PCR was sensitive in detecting respiratory virus than culture.27
Real time PCR combines the standard PCR method with fluorescent probe detection of the amplified product in the same reaction vessel28. Since the amplified product detection is also done simultaneously, results can be obtained very fast, so that specific treatment decisions can be done based on the results. The sensitivity and specificity of real time PCR is equivalent to that of conventional PCR. Real time PCR can also be used to detect the DNA quantitatively and thus will be able to differentiate between colonization and infection. In a study on 86 non-HIV immunocompromized patients 17 were diagnosed as having Pneumocystis pneumonia.  Induced sputum was obtained from the patients and it was evaluated for the presence of P.jiroveci DNA using conventional PCR and real time PCR. Conventional PCR had a high false positive rate of 46.4% as it was positive in patients with colonization also29. Concentration of DNA detected by real time PCR was significantly higher in Pneumocystis patients than in colonizers.
PCR is not recommended for the diagnosis of pneumococcal pneumonia as currently available PCR methods lack sensitivity and specificity and there are no FDA approved PCR tests for S. pneumoniae (Table-3). For the diagnosis of M.pneumoniae the sensitivity of PCR is less compared to serology30. But the advantage over serology is that the results can be obtained in a few hours.

Study
PCR
Culture
Massimo Resti et al
45(15.4%) of 292
11(3.8%) of 292
Deng J et al
32 of 176 (S.pneumoniae)
29 0f 176 (H. Influenza)
7 of 176
23 of 176
Rosario Menedez et al
41 of 184(S.pneumoniae-blood)
7 of 184
Allin Uskudar Guclu
67 0f 107(62.6%)
33 0f 107(31%)
Mervat Gamal Eldin Mansour
( Nosocomial pneumonia)

19 of 25 (76%) endotracheal aspirate
17 of 25 (68%) blood
6 of 25(24%)endotracheal aspirate
2 of 25(8%) blood
Templeton KE et al(virus)
87 0f 358(24%)
67 of 358 (19%)
Table-3: Comparative outcome of PCR and culture in community acquired pneumonia 31, 32, 33, 34
For the diagnosis of tuberculosis by PCR, FDA approval has been obtained, and is commercially available. It is most useful in patients with positive acid fast smears. A negative PCR in a smear negative patient will not rule out tuberculosis. Majority of PCR for M.tuberculosis detect Mycobacterium tuberculosis complex and do not differentiate the species within the complex. Halse TA et al was able to differentiate the species based on a real time PCR method35. Many novel multiplex real times PCR have been developed for the differentiation of Mycobacterium tuberculosis complex strains36. Compared to the conventional and rapid culture methods PCR can provide the results in a few hours.
The area where PCR has greatest impact on pathogen identification in pneumonia is in the identification of respiratory viruses. Viruses are usually neglected cause of community acquired pneumonia as they are difficult to isolate and treatment with anti-viral agents are not routinely recommended. However recently there had been few viral epidemics like Hantavirus in New Mexico, Severe Acute Respiratory Syndrome (SARS) in Asia, and the world wide H1N1 epidemic of 2009, where an etiological diagnosis was important clinically and epidemiologically.37
At present PCR is the most sensitive diagnostic method for respiratory viruses. Reverse transcriptase (RT-PCR) is used to detect RNA viruses. Reverse transcriptase enzyme is used to synthesize a complimentary strand of DNA from RNA, and this DNA is used as the template in PCR assay.
In a study of community acquired pneumonia in which PCR for viruses, Legionella, Mycoplasma and Mycobacterium tuberculosis, and urinary antigen for S pneumoniae and Legionella pneumophila serogroup 1, a microbial etiology was obtained in 67%.3 An etiologic diagnosis was obtained in 89% of patients in whom all diagnostic methods were applied.  In this study viruses were the second most common etiologic agent after S pneumonia. So by combining PCR with traditional diagnostic method, viruses are more frequently being recognized as etiologic agent of community acquired pneumonia.
The major problem with PCR assay is the risk of false positive results. This can result from contamination by exogenous material or by detection of colonizing organisms as a result of the extreme sensitivity of PCR assay.

Serology
Serologic tests may be useful to establish the cause of pneumonia when the causative agents are difficult to isolate. But a single antibody titre is not enough for the microbiologic diagnosis.  A four fold or greater rise in titre between acute and convalescent sera is required for the diagnosis. So it is not useful in the initial antibiotic selection for treatment. The antibodies may persist for months or years after an initial infection in Legionella infection. So a single titre of 1:256 or higher may reflect a prior Legionella infection. Serology tests may be useful for the epidemiologic diagnosis. The commonly diagnosed infections by serology are L.pneumophila, C.psittaci, M.pneumoniae, C.burnetti and F.tularensis. Serologic tests may also be useful in the retrospective diagnosis of infections due to Influenza A and B, Respiratory syncytial virus, adenovirus and parainfluenza virus.
Levels of IL-1β and IL-8 in bronchoalveolar lavage fluid (BALF) are one of the strongest markers investigated for accurately identifying VAP. Based on this, it is possible to reduce unnecessary antibiotics in suspected VAP patients, but this requires further validation in larger populations38. Mid-regional pro-atrial natriuretic peptide (MR-proANP) and C-terminal pro-atrial vasopressin (CT-proAVP) estimation are the new and emerging tools for the prediction of short-term and long-term risk stratification of patients with CAP.39

Invasive Diagnostic Procedures

Routine diagnostic procedures are used to establish the diagnosis of pneumonia in a patient with suggestive signs and symptoms, and also to identify the causative agent as far as possible. But the positive yield of these routine tests such as sputum and blood culture is often low so that clinician seldom depends on these tests.  Better positive outcome is achieved with lower respiratory tract sample for which invasive procedures are required. Invasive diagnostic procedures are advised in pneumonia in the following situations
·                     Slowly resolving or non resolving pneumonia
·                     Patients having life-threatening complications
·                     Pneumonia in immuno-compromised host
·                     Hospital acquired or ventilator associated pneumonia
Invasive procedures include:

(i)  Thoracentesis
(ii) Transthoracic Needle aspiration
(iii) Bronchoscopic Procedure
          a) Bronchoscopic BAL
          b) Bronchoscopic PSB
(iv) Non Bronchoscopic Procedures
a) Blind Bronchial aspirate
b) Blind BAL
c) Blind PSB
(v) Lung Biopsy
 (i) Thoracentesis:
It is reported that parapneumonic effusions are seen in more than 40% of patients with bacterial pneumonia. It is more common in pneumococcal pneumonia; seen in up to 60% of patients. Small pleural effusions are seen in viral and mycoplasma pneumonia, in up to 20% of patients. S. aureus is the commonly isolated organism in empyema thoracis in post-surgical patients40 If there is associated pleural effusion or empyema, every effort should be taken to retrieve adequate quantity of fluid for establishing an etiological diagnosis. Diagnostic thoracentesis can aid in the diagnosis and treatment plan for almost all pleural effusions. The exceptions to this rule are patients with a very small effusion41. All parapneumonic effusions having a thickness of >10 mm on the lateral decubitus x-ray, ultrasound or CT scan should be subjected for sampling.

Pleural fluid studies
  • Blood cell count (WBC count) and differential count generally help in differentiating between transudate and exudate. WBC counts in empyema are generally more than 50,000 cells/µL.
  • Pleural fluid total protein, LDH, and glucose estimation are also useful for differentiating between exudates and transudates.
  • Pleural fluid pH: Values of less than 7.20 are suggestive of a complicated pleural effusion.
  • Microbiology: Gram stain, Acid-fast bacilli stain and bacterial culture are essential investigations to prove the causative pathogen.

(ii) Bronchoscopic techniques:
Bronchoscopic procedure is used for collecting secretions from lower airways by either protected specimen brush (PSB) or Bronchoalveolar lavage (BAL). This will give a sample of uncontaminated specimen for culture and sensitivity. This specimen is used for either quantitative or qualitative culture.  In a study on 76 patients with VAP by Montravers et al, specimens for culture were collected using PSB. The diagnosis of pneumonia was confirmed by a bacteria count of ≥ 103 cfu/ml42. The clinicians’ initial antibiotic choice was modified on the basis of bronchoscopy results. However, it is not proved beyond doubt whether this information leads to improved outcome. In another study by Luna et al43 quantitative BAL was done and an etiologic organism was identified in 65 of 132 patients (49%). More than half of the patients among this group were already on antibiotic treatment for either community-acquired pneumonia or nosocomial pneumonia.
Quantitative cultures have been demonstrated to have good diagnostic utility for the presence of pneumonia, especially in patients with a low or equivocal clinical suspicion of infection44. In a study on VAP patients by Rello et al 45, out of a total of 113 patients, an organism was identified by bronchoscopy in 88% of patients. Out of this, 27 patients had an initial inadequate antibiotic therapy, and the mortality rate was significantly higher in this group. Consistent recovery of potential pathogens with invasive techniques can identify patients at high risk of mortality.
The major problem on relying culture reports for treating patients is that a negative culture can result in denying treatment to a specific patient or a specific pathogen. In a prospective study by Gibot and coworkers on 148 patients on mechanical ventilation, with suspected infectious pneumonia, a rapid immunoblot technique was done on BAL fluid, and it was found that levels of soluble triggering receptor expressed on myeloid cells (sTREM-1) was the strongest independent predictor of pneumonia.46. To differentiate between infection and colonization the diagnostic threshold varies with the technique used. Bronchoscopic BAL uses a diagnostic threshold of 104 or 105 cfu/ml. PSB samples require a diagnostic threshold of 103 cfu/ml or more. PSB is more specific than sensitive for diagnosing pneumonia48.
(iii) Non bronchoscopic technique
The non-bronchoscopic technique involves passage of a catheter through the endotracheal tube and then it is advanced and wedged into the bronchus. Samples are taken with a catheter containing a brush (blind PSB), 49or by aspiration of secretions through a distally wedged catheter., BAL may be performed by using a balloon-tipped catheter with the balloon inflated after the catheter has been advanced to the wedged position (protected BAL).The yield of bronchoscopic and non-bronchoscopic technique for obtaining quantitative cultures of lower respiratory specimens is comparable50. The choice depends on local resources and expertise.
(iv) Lung Biopsy.
In very severe cases of pneumonia or when the diagnosis is not clear, particularly in patients with a damaged immune system, a lung biopsy may be required. This can be done by bronchoscopic biopsy, needle aspiration, open lung biopsy or video assisted thoracoscopic biopsy. Open lung biopsy through a very limited anterior thoracotomy is employed in the diagnosis of P jeroveci pneumonia (PJP). Gaensler and co-workers51 have already shown the high yield of positive diagnoses by this procedure in diffuse pneumonic processes. Early open lung biopsy with frozen section staining should be undertaken at the first opportunity. Routine permanent section stains and cultures of lung tissue for bacteria, fungi, and acid-fast bacilli should also be performed.
(v) Transthoracic needle aspiration (TNA)
Moser et al52 demonstrated in an experimental model of dog with pneumococcal pneumonia that TNA has the best sensitivity and specificity rate. Furthermore, TNA is an easy procedure to carry out with very few complications and well tolerated by most of the patients. Ultrasound guided percutaneous cutting biopsy is a valuable method for diagnosing pulmonary consolidation of unknown aetiology. The diagnostic yield is high and the procedure appears to be relatively safe.



Diagnostic Imaging in Pneumonia

 (i) Chest Radiograph

Chest radiography is the most important investigation among the routine procedures employed for evaluating pneumonia. Patients who presented with fever, chills, and rusty sputum, and whose chest radiograph showed parenchymal infiltrates were considered to have typical pneumonia. Chest radiographs are sometimes useful for suggesting the etiologic agent, prognosis, alternative diagnoses, and associated conditions. Even though Chest X-ray can be considered as a gold standard for diagnosing pneumonia, it is taken in only 11% of cases in clinical practice. Studies also have shown that clinical judgment in ordering a chest x-ray is 100% sensitive and thus that all patients with pneumonia have been correctly identified. 53
Radiologic phases
It is indeed interesting to note that the radiological findings to a large extent correspond to the pathologic stages of pneumonia. In the initial phase lasting approximately 24 hours there is active hyperemia. In the next phase known as red hepatization, neutrophils and fibrin material fill the alveoli along with red blood cells resulting in a homogenous opacity. This is followed by gray hepatization when fibrin and exudative cells accumulate, seen in radiographs as a clear zone adjoining alveolar and acinar shadows. If the process extends to the pleural space, associated parapneumonic effusion (PPE) may be present. Finally the radiological shadow is cleared as the pneumonia resolves, but always there is a time lag between clinical resolution and radiological resolution.
Radiologic pattern

1) Airspace Pneumonia
Airspace Pneumonia is seen as homogenous consolidation, relatively sharply demarcated from adjacent uninvolved parenchyma which characteristically crosses segmental boundaries54.It usually abuts interlobar fissure but seldom involves entire lobe. When there is enormous exudation, expansion of the affected lobe occurs which is seen as bulging fissure 55.Since the conducting airways are patent air lucency can be seen through the opacities (Air bronchogram). Characteristic "silhouette" sign (Fig-3 & 4) obliterating cardiac or diaphragmatic border help in localizing the pneumonia.56
Rarely, it appears as spherical pneumonia, which is a solitary round nodule with or without hilar lymphadenopathy. This lesion is mostly seen in the posterior parts of the lung.57

2) Bronchopneumonia

Bronchopneumonia is a focal peribronchial or peribronchiolar area of consolidation involving one or more segments of a single lobe to multilobar bilateral consolidation 57,58.This is seen as poorly defined centrilobular nodular opacities measuring 4-10 mm with air alveologram or may involve the entire secondary lobule (Lobular consolidation)59. Bronchopneumonia frequently results in loss of volume of affected segment or lobe. Confluence of pneumonia in adjacent lobule may be extensive and may result in a pattern simulating non segmental airspace pneumonia.

3) Interstitial Pneumonia

Here diffuse, patchy ground-glass opacities are seen associated with linear or reticular opacities. (Fig-5) Characteristic findings are seen as 1-5 mm, poorly defined nodules and patchy peribronchial opacity and airspace consolidation. Patchy unilateral or bilateral consolidations and ground glass opacity or poorly defined centrilobular nodules are often seen in viral pneumonia.
Typical versus atypical pneumonia
Bacterial pneumonias are usually lobar, and there can be cavitation and pleural effusion. Multilobar involvement with nodular or reticular infiltrates, lobar or segmental collapse or perihilar adenopathy are seen in infection with atypical pathogens. But it is not possible to definitely differentiate between typical and atypical pneumonia based on radiologic findings. Therefore, the radiographic findings described above should be used along with clinical and laboratory data to narrow the possibilities.
The typical description of dense parenchymal shadow with air bronchogram is seldom seen in children. Mostly it is unilateral or bilateral alveolar shadows or interstitial infiltrates60. In their study Drummond et al 61 could not find any significant difference in  aetiology among the five radiographic groups into which their cases were divided (lobar consolidation, patchy consolidation, increased perihilar and peribronchial markings, pneumonitis and effusion). In another study by Korppi et al62 on 101 Italian children, no association was found between radiographic findings and etiology.
Structural lung disease with abnormal lung parenchyma affects the pattern of infiltrates. In cases of hyperinflation as in severe emphysema, there is a chance to underestimate the radiographic infiltrates. Shadows are usually patchy due to partial filling of enlarged airspaces. There will be large areas of involvement, unilateral or bilateral where air space opacities are interrupted by radiolucency (resembles Cheddar cheese)
The time required for the opacity to appear on chest radiographs in pneumonia is controversial. Usually the opacities appear within 12 hours. But in community acquired pneumonia, by the time the patient is referred to the radiologist for X-ray, adequate time will be usually lapsed for its detection. But in suspected nosocomial pneumonia, chest radiograph may be taken within a few hours, when opacity may not yet be visible63.  Similarly in a dehydrated patient shadows may not be apparent even with extensive involvement. In immunosuppressed patients also, especially those with coexistent neutropenia, diabetes, alcoholism, or uremia, the appearance of infiltrates may be delayed.
     

Non resolving Pneumonia

The terms nonresolving and slowly resolving pneumonia have been used interchangeably to refer to persistence of radiographic abnormalities beyond the expected time course64. The expected time course for resolution is controversial, and variable definitions have been set arbitrarily by investigators. In a 1987 review, Fein et al 65 defined non-resolving pneumonia as a clinical syndrome in which focal infiltrates clearly begin with some clinical association of acute pulmonary infection and do not resolve in the expected time. Non-resolving pneumonia should be considered when the patient fails to improve clinically, or when the radiological resolution is slow despite adequate and appropriate antibiotic therapy. Arbitrarily 4 weeks is considered as the cut off period for expressing radiological non resolution. About 10% of diagnostic bronchoscopy procedures and 15% of pulmonary consultations are performed to evaluate a nonresolving infiltrate. Rather than the infecting pathogen, it is usually the host defense that is responsible for delayed resolution. Host factors that may contribute to delayed resolution include age more than 50 years, smoking, chronic diseases like diabetes mellitus, renal failure, chronic obstructive pulmonary disease (COPD) and alcoholism. Consolidation persisted at 30 days in 27% of patients older than 50 years, compared with 18% among younger patients.65
Despite initial antibiotic therapy, during the early phase of the illness there can be radiological worsening, which is more common in bacteremic patients compared to non-bacteremic patients. According to the recommendation by Jay and colleagues66, the appropriate interval for repeating chest radiograph is 6 weeks, unless otherwise indicated by patient’s clinical worsening. In patients above 50 years, with COPD and alcoholism, 60% of patients have an abnormal chest radiograph at 14 weeks. But in patients below 50 years with bacteremia, 40% have an abnormal chest radiograph at 2 weeks.  Taking both groups together, 37% have residual radiological lesion at 4 weeks, and complete resolution was found in almost all patients by 18 weeks.
 Community acquired Pneumonia

S.pneumoniae is the etiologic agent responsible for 10-50% of community acquired pneumonia. Alveolar consolidation begins in the peripheral airspaces. It usually causes lobar or segmental consolidation, but patchy bronchopneumonic pattern is seen in the elderly. Pneumococcal pneumonia has a tendency to involve pleura in the early course of disease leading to parapneumonic effusion.66
The characteristic finding in staphylococcal pneumonia in children is the presence of pneumatoceles. Pneumatoceles may develop rapidly and there can be rapid progression with multilobar involvement. Empyema is also frequently seen in staphylococcal pneumonia. 67
Radiographically it is difficult to differentiate H.influenza from pneumococcal pneumonia. Multilobar infiltrate is common and pleural effusion is seen in 50% of cases. Resolution is usually slow. Klebsiella pneumonia present as patchy bronchopneumonia or dense lobar consolidation. The alveoli are frequently filled with large amounts of exudates and may cause an increase in the volume of the affected lobe with resultant bulging of the interlobar fissures, radiologically producing the bulging fissure sign or sagging fissure sign (Fig-6). Though these findings were thought to be characteristic of klebsiella pneumonia, they may be seen in other pneumonia also68. Abscess formation and cavities develop rapidly in klebsiella pneumonia and pleural effusion is also common.  
Tuberculous pneumonia present as lobar or segmental consolidation and development of cavity is quite common. Even though upper lobes are the common site, any part of the lung may be involved. The most common sites of cavity development are both upper lobe and apical segment of lower lobe (Fig-7). Diffuse miliary shadowing suggests disseminated disease. In immunosuppressed patients radiographic findings are more of a disseminated disease with acinar nodules or miliary shadows distributed predominantly in the lower zones. Findings such as tuberculous rnediastinitis, mass like densities mimicking carcinoma, tuberculornas, chronic lower lobe infiltrates, miliary tuberculosis, bronchopleural fistula, pleural effusion, and negative chest radiographs have been reported to occur in up to one-third of new adult cases of pulmonary tuberculosis 69. Another report in the radiologic literature suggested that up to 22% of patients with cavitary disease may have air-fluid levels 70.
Legionella pneumonia typically causes a patchy localized infiltrate in the lower lobes with associated hilar adenopathy. Rarely cavitation and mass like appearance are seen. In up to 30% of cases pleural effusion is reported. It may take longer duration for the complete resolution of legionella pneumonia. As long as 6-12 months may be needed for resolution, and residual fibrosis is seen in as many as 25% of patients71. Mycoplasma pneumoniae is another common cause of community acquired pneumonia Unilateral or bilateral infiltrates with hilar adenopathy may be seen and pleural effusion is reported in about 20% of cases. Extensive radiographic infiltrates may be seen in elderly patients. In up to 40% of patients radiological infiltrates resolve by 4 weeks and in 80% of the patients by 8 weeks72. Residual radiological lesions are uncommon.
Characteristic radiographic findings in fungal pneumonia include patchy infiltrates, nodules, consolidation, cavitation, or pleural effusion.  Radiological presentation of Aspergillosis and mucormycosis can be as round pneumonia with irregular margins which can slowly increase in size and number. It may progress to hemorrhagic pulmonary infarction73. Miliary nodular pattern is seen in disseminated infection. Non-resolving pneumonia leading to lung abscess is always a challenge to the treating physician especially in a diabetic patient. Atypical radiological features of lung abscess should raise the suspicion of unusual organisms. Rare fungus like basidiobolus can cause pneumonia and lung abscess in immuno-compromised individuals.74  
Radiographic manifestations of viral pneumonia are protean75 and usually present as bilateral bronchopneumonia and overinflation. Radiological resolution usually occurs in 2 weeks76. Radiographic manifestation of influenza pneumonia may range from mild interstitial prominence to patchy areas of consolidation and extensive airspace consolidation. Pleural effusion and cavity formation is rare and if present indicates bacterial superinfection.  Hanta virus pneumonia show interstitial edema with or without progression to airspace disease, with a central or bibasilar distribution and pleural effusions.
In anaerobic bacterial pneumonia infiltrate with or without cavitation will be seen in one of the dependant segments of the lung ie, posterior segment of upper lobe or superior segment of lower lobe. Cavitation suggests necrotizing pneumonia. Air fluid level in a circumscibed infiltrate suggests a lung abscess or bronchopleural fistula.

Hospital acquired Pneumonia:
Hospital acquired pneumonia (HAP) is diagnosed by the appearance of a new parenchymal infiltrate after 48 hours of hospitalization. X ray may show airspace consolidation, interstitial pattern or mixed shadows. It is difficult to differentiate atelectasis from HAP and the two may co exist. As many as 60% ventilated patients with the clinical diagnosis of pneumonia has some other process causing abnormalities in the chest radiograph 77. For the diagnosis of pneumonia in ventilated patients portable chest radiograph is mandatory, but its sensitivity and specificity is low. Usually the quality of the film is poor and it is difficult to diagnose pneumonia. Cavitation of pulmonary infiltrate, air space opacification, and localized air bronchogram are highly suggestive of VAP78.  

Aspiration Pneumonia
 Depending on the position of the patient during the time of aspiration79, the site of aspiration pneumonia varies. Due to the vertical orientation and larger diameter, the common site of aspiration pneumonia is middle and lower lobe of right lung. In the standing position bilateral lower lobe infiltrates is common. Left sided pneumonia is common if the patient was in the left lateral position. In prone position the right upper lobe is the common site for aspiration. Chest radiographic findings in patients with anaerobic bacterial pneumonia typically demonstrate an infiltrate with or without cavitation.
Pneumonia in immuno compromised Host
The chest film in Pneumocystis jerovci pneumonia typically shows diffuse, fine, reticular interstitial or perihilar opacification which may appear somewhat granular. This will progress to airspace consolidation over 3-4 days. This appearance may be followed by coarse reticulation as the pneumonia resolves.80 Chest radiograph findings may be normal in 10-39% of patients, or radiographic changes may lag behind the clinical symptoms.
Pneumatoceles increase the risk of pneumothorax81. Less commonly, lobar infiltrates, effusions or cavitary lesions mimic other pulmonary processes.82 Atypical radiographic manifestations include cystic lung disease, spontaneous pneumothorax and lobar or segmental consolidation with upper lobe predominance. Pleural effusions and hilar lymphadenopathy are uncommon. Cyst formation is seen more frequently in HRCT (33%) rather than in chest radiographs (10%).
Chest radiographs in an immuno compromised patient with CMV pneumonia reveal an interstitial pattern of disease, which is usually diffuse and which involves the bases. The interstitial pattern consists of accentuation of Kerley A and Kerley B lines or of diffuse, hazy, ground-glass opacities.83

 (ii) Computed Tomography


CT scanning provides a better definition of the diseased areas and is used to differentiate parenchymal abnormalities from pleural abnormalities. Computed tomography (CT) scan is not routinely employed in the diagnosis of pneumonia and is indicated in specific situations involving the following. 84
·                                 Non resolution/ Delayed resolution of pneumonia
·                                 An indistinct, abnormal opacity on chest radiographs
·                                 Patchy, ground-glass, linear, or reticular opacities on chest radiographs
·                                 Possible pleural effusion
·                                 Neutropenia and fever of unknown origin
High resolution CT findings in CAP
Tanaka et al compared high resolution CT (HRCT) scan findings in CAP with pathologic findings and evaluated its role in differentiating between bacterial and atypical pneumonias in 32 patients with CAP.85 Consolidation or cavitating nodules were seen on CT and the nodules varied in size from 1 mm to 3 cm.86 The nodules had irregular or smooth margin without any zonal predominance. Tree in bud pattern was also seen87. Majority of patients (88%) had ground glass opacification and all lobes were equally involved.
Bacterial pneumonia often showed a pattern of airspace consolidation with segmental distribution (72%) that typically distributed towards the middle and outer zones of the lungs (Fig-8). In tuberculous pneumonia area of consolidation is seen in 52.8 %. Bronchogenic dissemination outside the consolidation appeared in 52.4%. Lymph node enlargement and pleural reaction were seen in 55.6 and 35.6%, respectively 88. Tree-in-bud pattern (Fig-9) is the most characteristic, but not pathognomonic feature of endobronchial spread of tuberculosis and can be found in 72% of patients with active disease 89.
Atypical pneumonia caused by Mycoplasma, Chlamydia and influenza virus causes centrilobular lesions, acinar shadows, consolidation or ground glass opacity. In majority of cases the lesions are distributed in the inner, middle, and outer layers of the lung.
CT manifestations of Legionella pneumonia include bilateral lung parenchymal involvement. Peripheral lung consolidation, ground glass opacity, lung cavitations and bulging fissures are also seen.  There can be residual lung parenchymal scarring63.  
 In a study on 28 patients by Reittner et al, ground-glass opacification as well as airspace consolidation were reported in majority of patients. Nodules were better delineated in HRCT compared to X-ray, and the nodules had a predominant centrilobular distribution. Thickening of bronchovascular markings were also better appreciated in CT thorax compared to chest x-ray72.
The usual CT findings in fungal pneumonia include patchy infiltrates, consolidation, cavity formation, nodules and pleural effusion. In disseminated disease miliary nodules may be seen. Unilateral or bilateral mediastinal adenopathy is commonly seen in endemic fungal pneumonia. HRCT scanning allows observation of the halo sign in patients with aspergillosis. This is a nodular lesion usually surrounded by a ground-glass opacity or halo. Greene and co workers reported halo sign in 61% of 235 patients with invasive aspergillosis88. Diagnosis may be difficult through imaging as many lesions are non-specific and also due the presence of parenchymal abnormalities from the underlying lung disease.
Ground-glass attenuation is the characteristic HRCT finding of Pneumocystis jerovci pneumonia (PJP). In more than 90% of patients, lesion are bilateral, symmetrical and perihilar in distribution. There may be geographic pattern with areas of normal lung adjacent to diseased lung (Dark bronchus sign).89

(iii) Ultrasonography

 The role of ultrasonography in pneumonia is mainly to differentiate between consolidation and pleural effusion. Consolidation appears as hypoechoic area with blurred margins. It becomes more heterogenous with aeration and in dense consoldation it will be homogenous. In a study by Bency et al consolidation was seen as large hypoechoic lesions or small round subpleural hypoechoic lesions. The sensitivity of ultrasound is similar to that of conventional radiography, but it is less useful in interstitial pneumonia90. The literature also reports that ultrasonography may aid in the diagnosis of  empyema and abscesses. However, most authors believe that in clinical practice, ultrasonography's usefulness is limited to the identification and quantification of parapneumonic effusions. This can correctly identify the site for subsequent diagnostic or therapeutic thoracentesis.
Summary
Community acquired pneumonia is diagnosed based on symptoms and signs and a radiographic abnormality. But certain situations warrant an etiological diagnosis which is mostly by microbiological intervention. However these tests are not always helpful especially when the patient was put on an initial antibiotic therapy or when atypical organisms or rarer organisms cause the pneumonia. Common tests are not routinely used due to low yield as well as infrequent positive impact on management decisions. It becomes more difficult to establish an etiology in hospital acquired pneumonia. Newer culture methods and molecular technique has been evolved which offers specific diagnosis that too in a shorter time frame. The composition of the diagnostic workup for pneumonia has been the subject of some disagreement for years, but a well-chosen, individually tailored evaluation can offer a lot of information to support the diagnosis of pneumonia.

References:

1.Sahn SA. Diagnosis and management of parapneumonic effusions and empyema. Clin Infect Dis. 2007; 45 (11):1480-6.
2.Fine MJ, Stone RA, Singer DE et al. Processes and outcomes of care for patients with community acquired pneumonia: Results from the Pneumonia Patient Outcomes Research Team cohort study. Arch Intern Med 1999;159:970-80 2
3.Johansson N, Kalin M, Tiveljung-Lindell A, Giske CG, Hedlund J. Etiology of community-acquired pneumonia: increased microbiological yield with new diagnostic methods. Clin Infect Dis. 2010 Jan 15;50(2):202-9

4.Murray PR, Washington JA. Microscopic and bacteriologic analysis of expectorated sputum. Mayo Clin Proc. 1975 Jun; 50 (6):339-44.

5.4. Carr DT, Karison AG, Stilwell GG. A comparison of cultures of induced sputum and gastric washings in the diagnosis of tuberculosis. Mayo Clin  Proc 1967,42:23-25.

6.Rosemeri Maurici da Silva, Paulo Jose Zimmermann Teixeira, Jose da Silva. The Clinical Utility of Induced Sputum for the Diagnosis of Bacterial Community-Acquired Pneumonia in HIV infected Patients. The Braz J Infect Dis 2006;10 (2):89-93.

7.Lahti E, Peltola V,  Waris M, et al. Induced sputum in the diagnosis of childhood community-acquired pneumonia. Thorax 2009;64:252-257.

8.Moyes RB, Reynolds J, Breakwell DP: Differential staining of bacteria: gram stain. Curr Protoc Microbiol 2009 Nov; 15: 1-8.

9.Michael D Iseman. Biology and Laboratory Diagnosis of Tuberculosis-A Clinicians Guide to Tuberculosis. Lippincott Williams & Wilkins 2000.Page 22, Chapter 2.

10.  Ba F, Rieder HL. A comparison of fluorescence microscopy with the Ziehl- Neelsen technique in the examination of sputum for acid- fast bacilli. Int J Tuberc Lun Dis 2008;3 (12):1101-1105.

11.  Steingart KR, Henry M, Ng V, Hopewell PC, Ramsay A, Cunningham J, et al. Fluorescence versus conventional sputum smear microscopy for tuberculosis: a systematic review. Lancet Infect Dis. 2006 Sep; 6 (9):570-81.

12.  Shlaes DM, Lederman MM, Chmielewski R, Tweardy D, Krause G, Saffai C.   Sputum elastin fibers and the diagnosis of necrotizing pneumonia : Chest,1984 Jun;85(6):763-66.

13.  Rodríguez de Castro F, Solé Violán J, Rey López A, Martín González JC, Acosta Fernández O, Caminero Luna JA, et alThe usefulness of elastin fibers as a diagnostic marker in ventilator-related pneumonia.Arch Bronconeumol. 1994 Apr;30 (4):188-91.

14.  Kim YK, Parulekar S, Yu PK, Pisani RJ, Smith TF, Anhalt JP Evaluation of calcofluor white stain for detection of Pneumocystis carinii.Diagn Microbiol Infect Dis. 1990 Jul-Aug; 13(4):307-10.

15.  Aslanzadeh J, Stelmach PS. Detection of Pneumocystis carinii with direct fluorescence antibody and calcofluor white stain. Infection. 1996 May-Jun; 24 (3):248-50.

16.  Mark L Metersky, Jaber Aslenzadeh, Paulette Stelmach; A comparison of induced and expectorated sputum in the diagnosis of Pneumocystis Carinii Pneumonia.Chest 1998; 113: 1555-1559.

17.  Rello J, Bodi M, Mariscal D, Navarro M, Diaz E, Gallego M, Valles J. Microbiological testing and outcome of patients with severe community-acquired pneumonia. Chest 2003 Jan; 123(1):174-80.


18.  Timothy H. Dellit, Robert C. Owens, John E. McGowan, Jr., Dale N. Gerding, Robert A. Weinstein, John P. Burke,et al: Infectious Diseases Society of America and the Society for Healthcare Epidemiology of America Guidelines for Developing an Institutional Programme to enhance Antimicrobial Stewardship. Clinical Infectious Diseases 2007; 44:159–77
19.  Samuel G. Campbell, Thomas J. Marrie, Rosemary Anstey, ART, et al. The Contribution of Blood Cultures to the Clinical Management of Adult Patients Admitted to the Hospital with Community-Acquired Pneumonia:A Prospective Observational Study. Chest 2003 ; 123 ( 4): 1142-1150
20.  Abe T, Tokuda Y, Ishimatsu S, Birrer RB. Usefulness of initial blood cultures in patients admitted with pneumonia from an emergency department in Japan. J Infect Chemother. 2009 Jun; 15(3):180-6.
21.  Waterer GW, Wunderink R.G. The influence of the severity of community-acquired pneumonia on the usefulness of blood culture. Respir Med 2001; 95:78 -82.

22.  Félix Gutiérrez, Masiá Mar, Carlos Rodríguez J, Antonio Ayelo, Bernardo Soldán, Laura Cebrián  et al. Evaluation of the Immunochromatographic Binax NOW Assay for detection of Streptococcus pneumoniae Urinary Antigen in a Prospective Study of Community-Acquired Pneumonia in Spain. Clinical Infectious Diseases 2003;36: 286-92.

23.  Domínguez J, Blanco S, Rodrigo C, Azuara M, Galí N, Mainou A . Usefulness of urinary antigen detection by an immunochromatographic test for diagnosis of pneumococcal pneumonia in children.J Clin Microbiol. 2003 May; 41(5):2161-63.

24.  Smith MD, Sheppard CL, Hogan A et al ,Diagnosis of Streptococcus pneumoniae infections in adults with bacteremia and community-acquired pneumonia: clinical comparison of pneumococcal PCR and urinary antigen detection. J Clin Microbiol. 2009 Apr; 47 (4):1046-69.

25.  Yu VL, Stout JE. Rapid diagnostic testing for community-acquired pneumonia: can innovative technology for clinical microbiology be exploited? Chest 2009;136 (6):1618-21.


26.  Falguera M,  Ruiz-González A,  Schoenenberger J A,  Touzón C, Gázquez I, Galindo C, et al. Prospective, randomised study to compare empirical treatment versus targeted treatment on the basis of the urine antigen results in hospitalized patients with community-acquired pneumonia.Thorax 2010; 65:101-106.
27.  Templeton KE, Scheltinga SA, Beersma MF, Kroes AC, Claas EC, Rapid and sensitive method using multiplex real-time PCR for diagnosis of infections by influenza A and influenza B viruses, respiratory syncytial virus, and parainfluenza viruses 1, 2, 3, and 4. J Clin Microbiol. 2004; 42 (4):1564-69.
28.  Espy M J,. Uhl J R, Sloan L M, et al. Real-Time PCR in Clinical Microbiology: Applications for Routine Laboratory Testing. Clin Microbiol Rev. 2006; 19(1): 165–256.

29.  Fujisawa T, Suda T, Matsuda H, Inui N, et al. Real-time PCR is more specific than conventional PCR for induced sputum diagnosis of Pneumocystis pneumonia in immunocompromised patients without HIV infection. Respirology 2009;14(2):203-9.

30.  Martínez MA, Ruiz M, Zunino E, et al. Detection of Mycoplasma pneumoniae in adult community-acquired pneumonia by PCR and serology. J Med Microbiol. 2008; 57:1491-95.

31.  Massimo Resti, Maria Moriondo. Community-Acquired Bacteremic Pneumococcal Pneumonia in Children: Diagnosis and Serotyping by Real-Time Polymerase Chain Reaction Using Blood Samples. Clin Infect Dis. 2010; 51 (9): 1042-49.
32.  Deng J, Zheng Y, Zhao R, Wright PF, Stratton CW, Tang YW. Culture versus polymerase chain reaction for the etiologic diagnosis of community-acquired pneumonia in antibiotic-pretreated pediatric patients Pediatr Infect Dis J.2009; 28(1):53-5.
33.  Rosario menéndez, Juan córdoba, Pilar de la cuadra, María j. cremades, José I. López-hontagas, Miguel salavert,et al. Value of the Polymerase Chain Reaction Assay in Noninvasive Respiratory Samples for Diagnosis of Community-Acquired Pneumonia. Am J Respir Crit Care Med 1999; 159:1868-73.

 

34.  Aylin Uskudar Guclu, Mehmet Baysallar, Ayse Gul Gozen, Abdulla Kilic, Arzu Balkan, Levent Doganci. Polymerase chain reaction vs. conventional culture in detection of bacterial pneumonia agents. Annals of Microbiol 2005; 55 (4): 313-16


35.  Halse TA, Escuyer VE, Musser KA. Evaluation of a single tube multiplexes real-time PCR for differentiation of members of the Mycobacterium tuberculosis complex in clinical specimens. J Clin Microbial. 2011; 49(7):2562-67

36.  Reddington K, O'Grady J, Dorai-Raj S, et al . Novel multiplex real-time PCR diagnostic assay for identification and differentiation of Mycobacterium tuberculosis, Mycobacterium canettii, and Mycobacterium tuberculosis complex strains. J Clin Microbiol.  2011;49 (2):651-7.

37.  Michael S. Niederman. Viral Community-Acquired Pneumonia: If We Do Not Diagnose It and Do Not Treat It, Can It Still Hurt Us? Chest 2010; 138 (4):767-69.
38.  Morris AC, Kefala K, Wilkinson T S, Moncayo-Nieto O L, Dhaliwal K, Farrell L, et al. Diagnostic importance of pulmonary interleukin-1β and interleukin-8 in ventilator-associated pneumonia. Thorax 2010; 65:201-207.
39.   Krüger S, Ewig S, Kunde J, Hartmann O, Suttorp N, WelteT, et al. Pro-atrial natriuretic peptide and pro-vasopressin for predicting short-term and long-term survival in community-acquired pneumonia: results from the German Competence Network CAPNETZ. Thorax 2010; 65:208-214.
40.  Grijalva CG, Zhu Y, Pekka Nuorti J, Griffin MR. Emergence of parapneumonic empyema in the USA. Thorax 2011; 66 (8):663-68.
41.  Rahman NM, Chapman SJ, Davies RJ. The approach to the patient with a parapneumonic effusion. Clin Chest Med. 2008; 27 (2):253-266.
42.  Montravers  P, Fagon  J, Chastre  J, et al. Follow-up protected specimen brushes to assess treatment in nosocomial pneumonia. Am Rev Respir Dis 1993; 147, 38-44.
43.  Luna C, Vujacich P, Niederman M, et al Impact of BAL data on the therapy and outcome of ventilator associated pneumonia. Chest 1997; 111:676-85.
44.  Heyland DK, Cook DJ, Marshall J, Heule M, Guslits B, Lang J, et al. Canadian Critical Care Trials Group. The clinical utility of invasive diagnostic techniques in the setting of ventilator-associated pneumonia. Chest 1999; 115:1076- 84.
45.  Rello J, Gallego  M, Mariscal  D, et al The value of routine microbial investigation in ventilator-associated pneumonia. Am J Respir Crit Care Med 1997;156,196-200.
46.  Gibot S, Cravoisy A, Levy B, Bene MC, Faure G, Bollaert PE. Soluble triggering receptor expressed on myeloid cells and the diagnosis of pneumonia. N Engl J Med 2004;350:451–58.

47.  Marquette CH, Herengt F, Mathieu D, Saulnier F, Courcol R, Ramon P. Diagnosis of pneumonia in mechanically ventilated patients: repeatibility of the protected specimen brush. Am Rev Respir Dis 1993; 147:211–214.

48.  Torres A, El-Ebiary M. Bronchoscopic BAL in the diagnosis of ventilator-associated pneumonia. Chest 2000;117(S):198–202

49.  Torres A, de la Bellacasa JP, Rodriguez-Roisin R, DeAnta MTJ, Agusti-Vidal A. Diagnostic value of telescoping plugged catheters in mechanically ventilated patients with bacterial pneumonia using the Metras catheter. Am Rev Respir Dis 1988; 138:117-20.

50.  Torres A, Ewig S. Diagnosing ventilator-associated pneumonia. N Engl J Med 2004; 350:433–435.

51.  Gaensler, E. A., Moister, M. V. B., and Hamm, J. Open-lung biopsy in diffuse pulmonary disease. N Engl J Med 1964; 270:1319-21

52.  Moser KM, Maurer J, Jassy L, Kremsdorf R, Konopka R, Shure D, et al. Sensitivity, specificity and risk of diagnostic procedures in a canine model of Streptococcus pneumoniae. Am Rev Respir Dis 1982; 125:436-42.

53.  Heckerling PS, Tape TG, Wigton RS, et al. Clinical prediction rule for pulmonary infiltrates. Ann Intern Med 1990; 113:664–670.

54.  Fraser RG, Wortzman G: acute pneumococcal lobar pneumonia.the significance of non segmenta distribution. J can Assoc radiol 1959; 10:37- 42.

55.  Barnes DJ, Naraqi S, Igo JD. The diagnostic and prognostic significance of bulging fissure in acute lobar pneumonia. Aust Nz J Med 1998; 170:1077- 1080.

56.  Felson B, Felson H. Localization of intrathoracic lesions by means of the postero-anterior roentgenogram; the silhouette sign. Radiology 1950; 55:363-374.
57.  Rose RW, Ward BH. Spherical pneumonias in children simulating pulmonary and mediastinal masses. Radiology1973; 106: 179-182.
58.  Karje MG,Fox MJ, Barlett JG et al. The clinical spectrum of staphylococcus aureus pulmonary infections. Chest 1990; 97:788- 792.
59.  Macfarlane J, Rose D. Radiographic features of staphylococcal pneumonia in adults and children. Thorax 1996; 51:539- 540.
60.  Ravindran C. Pneumonia. Paediatric Respiratory Illness. Ravindran chetambath (I ed), Macmillan Medical Communications, Gurgaon 2011; (I ed): 105-113.
61.   Drummond , Clark J, Wheeler J,  Galloway A,  Freeman R,  Cant A. Community acquired pneumonia—a prospective UK study. Arch Dis Child 2000; 83:408-412.
62.  Korppi M, Don M, Valent F, Canciani M. The value of clinical features in differentiating between viral, pneumococcal and atypical bacterial pneumonia in children. Acta Paediatr. 2008; 97(7):943-947.
63.  Hagaman JT, Rouan GW, Shipley RT, Panos RJ. Admission chest radiograph lacks sensitivity in the diagnosis of community-acquired pneumonia. Am J Med Sci. 2009; 337(4):236-240.
64.  Kirtland SH, Winterbauer RH: Slowly resolving, chronic and recurrent pneumonia. Clin Chest Med 1991; 12:303-318.
65.   Fein AM, Feinsilver SH, Niederman MS: Non-resolving and slowly resolving pneumonia. Diagnosis and management in the elderly patient. Clin Chest Med 1993;14:555-569.
66.  Jay SJ, Johanson WG Jr, Pierce AK: The radiographic resolution of Streptococcus pneumoniae pneumonia. N Engl J Med 1975; 293:798-780.
67.   Don M, Canciani M, Korppi M. Community-acquired pneumonia in children: what's old? What’s new? Acta Paediatr. 2010; 99(11): 1602- 1608.
68.   Francis JB, Francis PB. Bulging (sagging) fissure sign in Hemophilus influenzae lobar pneumonia. South Med J. 1978; 71(11):1452-53.
69.  Miller WT, MacGregor AR. Tuberculosis: frequency of unusual radiographic findings. AJR 1978; 130:867-875.
70.  Cohen JA, Amorosa JK, Smith PR. The air fluid level in cavitary pulmonary tuberculosis. Radiology 1978; 127:315-316.
71.  Macfarlane JT, Miller AC, Roderick Smith WH, et al: Comparative radiographic features of community-acquired Legionnaires' desease, pneumococcal pneumonia, Mycoplasma pneumonia, and psittacosis. Thorax 1984; 39:28-33.
72.  Reittner P, Muller NL, Heyneman L, et al. Mycoplasma pneumoniae pneumonia: radiographic and high-resolution CT features in 28 patients. AJR Am J Roentgenol. 2000; 174(1):37-41.
73.  Libshitz H I, Pagani J J. Aspergillosis and mucormycosis: two types of opportunistic fungal pneumonia. Radiology 1981 140 (2) :301-306
74.  Chetambath R, Deepa Sarma MS, Suraj KP, Jyothi E, Mohammed S, Philomina BJ, Ramadevi S. Basidiobolus: An unusual cause of lung abscess. Lung India 2010; 27:89-92.
75.  Franquet T. Imaging of Pulmonary Viral Pneumonia. Radiology 2011; 260(1) 18-39.
76.  Farng KT, Wu KG, Lee YS, et al. Comparison of clinical characteristics of adenovirus and non-adenovirus pneumonia in children. J Microbiol Immunol Infect. 2002; 35(1):37-41.
77.  Lownkron SE, Niedermann MS. Definition and evaluation of the resolution of nosocomial pneumonia.Semin Respir Infec 1992; 7:271.
78.  Wunderink R G, Woldenberg L S, Zeiss J, Day C M., Ciemins J, Lacher DA. The radiologic diagnosis of autopsy-proven ventilator-associated pneumonia. Chest 1992; 101:458-463.
79.  Marom EM, McAdams HP, Erasmus JJ, Goodman PC. The many faces of pulmonary aspiration. AJR Am J Roentgenol. 1999; 172 (1):121-128.
80.  Crans CA Jr, Boiselle PM. Imaging features of Pneumocystis carinii pneumonia. Crit Rev Diagn Imaging. 1999;40(4):251-84.
81.  Metersky ML, Colt HG, Olson LK, Shanks TG.  AIDS-related spontaneous pneumothorax: risk factors and treatment.  Chest.  1995; 108:946–951.
82.  Opravail  M, Marincek  B, Fuchs  WA, Weber  R, Speich  R, Battegay  M, et al.  Shortcomings of chest radiography in detecting Pneumocystis carinii pneumonia.  J Acquir Immune Defic Syndr.  1994; 7:39–45.
83.  Eddleston M, Peacock S, Juniper M, Warrell DA. Severe cytomegalovirus infection in immunocompetent patients. Clin Infect Dis. 1997; 24(1):52- 56.
84.  Heussel CP, Kauczor HU, Heussel G, et al. Early detection of pneumonia in febrile neutropenic patients: use of thin-section CT. AJR Am J Roentgenol. 1997;169(5):1347-53.
85.  Tanaka N, Matsumoto T, Kuramitsu T, et al. High resolution CT findings in community-acquired pneumonia. J Comput Assist Tomogr. 1996; 20(4):600- 608.
86.  Sarji A, Abdullah WW, Wastie ML Imaging features of fungal infection in immuno-suppressed patients in a local ward outbreak Biomed Imaging Interv J 2006; 2 (2):e21.
87.   Eisenhuber E. The Tree-in-Bud Sign. Radiology 2002; 222: 771-772.
88.  Greene RE, Schlamm HT, Oestmann JW, Stark P, Durand C, Lortholary O, et al. Imaging findings in acute invasive pulmonary aspergillosis: clinical significance of the halo sign. Clin Infect Dis. 2007; 44(3):373-79.
89.   Poonam Yadav, Ashu Seith, Rita Sood. The ‘dark bronchus’ sign: HRCT diagnosis of Pneumocystis carinii pneumonia Ann Thorac Med. 2007; 2(1): 26–27.

90.  Benci A, Caremani M, Menchetti D, Magnolfi AL Sonographic diagnosis of pneumonia and bronchopneumonia. European Journal of Ultrasound 1996;4(3) 169-176.


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