Both confirmation of the diagnosis and assessment of the likely etiology are required. Although no data have demonstrated that treatment directed at a specific pathogen is superior to empirical treatment, an etiologic diagnosis allows narrowing of the empirical regimen, identification of organisms with public safety implications (e.g., Mycobacterium tuberculosis, influenza virus), and monitoring of antibiotic susceptibility trends.
- Chest radiography is often required to differentiate CAP from other conditions, particularly since the sensitivity and specificity of physical exam findings for CAP are only 58% and 67%, respectively.
- - CT of the chest may be helpful for pts with suspected postobstructive pneumonia or suspected cavitary disease.
- - Some radiographic patterns suggest an etiology; e.g., pneumatoceles suggest S. aureus.
- Sputum samples must have >25 WBCs and <10 squamous epithelial cells per high-power field to be appropriate for culture. The sensitivity of sputum cultures is highly variable; in cases of proven bacteremic pneumococcal pneumonia, the yield of positive cultures from sputum samples is ≤50%.
- Blood cultures are positive in 5-14% of cases, most commonly yielding S. pneumoniae. Blood cultures are optional for most CAP pts but should be performed for high-risk pts (e.g., pts with chronic liver disease or asplenia).
- Urine antigen tests for S. pneumoniae and Legionella pneumophila type 1 can be helpful.
- PCR of nasopharyngeal swabs has become the standard for diagnosis of respiratory viral infection and is also useful for detection of many atypical bacteria.
- Serology: A fourfold rise in titer of specific IgM antibody can assist in the diagnosis of pneumonia due to some pathogens; however, the time required to obtain a final result makes serology of limited clinical utility.
Treatment: Community-Acquired Pneumonia Deciding Whether to Hospitalize PTS - Two sets of criteria identify pts who will benefit from hospital care. It is not clear which set is superior, and application of each tool should be tempered by a consideration of factors relevant to the individual pt.
- - Pneumonia Severity Index (PSI): Points are given for 20 variables, including age, coexisting illness, and abnormal physical and laboratory findings. On this basis, pts are assigned to one of five classes of mortality risk.
- - CURB-65: Five variables are included: confusion (C); urea >7 mmol/L (U); respiratory rate ≥30/min (R); blood pressure, systolic ≤90 mmHg or diastolic ≤60 mmHg (B); and age ≥65 years (65). Pts with a score of 0 can be treated at home, pts with a score of 2 should be hospitalized, and pts with a score of ≥3 may require management in the ICU.
Antibiotic Therapy - For recommendations on empirical antibiotic treatment of CAP, see Table 132-1. U.S. guidelines always target S. pneumoniae and atypical pathogens. Retrospective data suggest that this approach lowers the mortality rate.
- Pts initially treated with IV antibiotics can be switched to oral agents when they can ingest and absorb drugs, are hemodynamically stable, and are improving clinically.
- CAP has historically been treated for 10-14 days, but a 5-day course of a fluoroquinolone is sufficient for cases of uncomplicated CAP. A longer course may be required for pts with bacteremia, metastatic infection, or infection with a particularly virulent pathogen.
- Fever and leukocytosis usually resolve within 2-4 days. Pts who have not responded to therapy by day 3 should be reevaluated, with consideration of alternative diagnoses, antibiotic resistance in the pathogen, and the possibility that the wrong drug is being given.
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