General Facts and Figures Classification Presentation History Physical Exam Labs Radiology Diagnosis Criteria for diagnosis Differential Microbiology General Specific organisms Pharmacology Drug classes Mechanism of action Resistance Treatment General Site of care Medication Duration Assessment of response Prevention References Literature cited Complete bibliography Links More...		Presentation Labs an etiologic organism is not identified in up to 50% of cases 9 exact incidences of the various etiologic organisms are not known; Mycoplasma, Chlamydia and viral pneumonias are difficult to diagnose and their incidence may be higher than reported 10 although its incidence is decreasing, S. pneumoniae remains the most commonly isolated pathogen in patients with pneumonia; the exact incidence varies but in a meta-analysis of 122 cases of CAP, it accounted for 66% of cases in which a microbiological diagnosis was made 11 IDSA guidelines recommend the following lab tests: OUTPATIENTS - sputum Gram stain is desirable, culture for conventional bacterial is optional INPATIENTS - above plus CBC w/diff, chemistry panel (including renal and liver function tests), HIV serology (with informed consent), ABG, pretreatment blood cultures (2), sputum Gram stain and culture, additional tests for selected patients (risk of M. tuberculosis, Legionnaire's disease, M. pneumoniae, or C. pneumoniae), thoracentesis (with stain, culture, pH determination, leukocyte count with differential); the recommendations also list alternative specimens to expectorated sputum and optional studies the usefulness of sputum Gram stain and culture has been debated because of the poor sensitivity and specificity of the tests; factors reducing specificity & sensitivity include: the difficulty in obtaining good specimens, the absence of purulent sputum in certain cases, a history of recent antibiotic use, the inability to detect certain organisms through these methods, and the need for expertise in evaluating the results 12 TABLE 2. IDSA recommendations for sputum collection, transport and processing 13 Collection: obtain a pretreatment specimen; it should be obtained by deep cough and be grossly purulent; obtain in the presence of a physician or nurse. Transport: specimen should be immediately transported to lab for prompt processing (delays of 2-5 hrs at room temperature result in reduced isolation rates for S. pneumoniae, S. aureus, and gram-negative bacilli with increased numbers of indigenous flora). Tests gram stain and culture (select purulent portion of specimen) quellung test (when available) cytological screening under low-power magnification (X100) to determine cellular composition (not useful for screening specimens for detection of Legionella or mycobacteria) culture should be performed by using standard techniques and reporting with semiquantitative assessment. sputum - proper collection is essential; the gross appearance may provide clues to the etiology (Table 3) TABLE 3. Clues from the sputum 14 foul smell oral anaerobes (aspiration) creamy yellow or salmon color S. aureus currant-jelly color pneumococcus, Klebsiella rasberry-syrup color pneumonic plague (Yersinia pestis) red color (pseudohemoptysis) Serratia blood-streaked (hemoptysis) Klebsiella influenza meningococcus pneumonic plague CBC - the absence of an elevated WBC does not rule out infection because certain patients may not be able to mount an adequate immune response blood cultures: certain pathogens are more likely to produce bacteremia (S. pneumoniae, H. influenzae) Footnotes: 9) Campbell GD, Overview of community-acquired pneumonia: prognosis and clinical features, Medical Clinics of North America 1994, 78:1035-1048. 10) Pomilla PV, et al., Outpatient treatment of community-acquired pneumonia in adults, Archives of Internal Medicine, 1994 Aug; 154:1793-1802. 11) Fine MJ, et al, Prognosis and outcomes of patients with community-acquired pneumonia, a meta-analysis, JAMA 1996 Jan 10;275:134-141. 12) Campbell GD, Overview of community-acquired pneumonia: prognosis and clinical features, Medical Clinics of North America, 1994, 78:1035-1048. 13) Bartlett JG, et al., Community-acquired pneumonia in adults: guidelines for management, The Infectious Diseases Society of America, Clinical Infectious Diseases, 1998 Apr, 26(4):811-38. 14) Karetzky M, et al., The Pneumonias, Springer-Verlag, New York, 1993.

medschool.ucsd.edu/curricular_resources/MED/CAP/index.html   3/30/99