In the appropriate clinical situation the diagnosis of CAP is established by demonstration of focal pulmonary findings, either by lung auscultation or by chest radiograph. Chest radiographs should be done in all patients with suspected CAP, because this test is useful in excluding complications (e.g., pleural effusions) and because associated findings may predict the pathogen (e.g., lymphadenopathy) or suggest alternative diagnoses (e.g., lung mass, lung abscess). When examined in a blinded fashion, the radiographic pattern does not reliably differentiate specific pathogens. This is particularly true among the elderly and immunocompromised patients, who may have unusual or no infiltrate in the setting of CAP. Radiographic improvement lags behind clinical response, and routine serial chest radiographs are not recommended unless the patient is not improving; however, all tobacco smokers and patients over the age of 65 should have follow-up chest radiographs 3–6 months after an episode of pneumonia in order to exclude an occult lung nodule.

    Various risk-stratification methods have been developed and validated to predict which patients are at sufficiently low mortality risk to justify home therapy, which costs 20-fold less than an inpatient stay. The easy-to-use CURB-65 risk score can be calculated on the basis of five simple features, including the presence of confusion (1 point), blood urea nitrogen (BUN) >30 mg/dL (1 point), respiratory rate ≥ 30 breaths per minute (1 point), systolic blood pressure <90 mm Hg or diastolic blood pressure <60 mm Hg (1 point), and patient age 65 or older (1 point). The risk of death or ICU admission increases with increasing CURB-65 scores (table 1.2).

    The Pneumonia Severity Index (PSI) is a validated risk stratification method that considers the risk contributions of patient demographic features (age having the greatest influence) and key physical examination and laboratory findings (table 1.3). Of note, other than a measurement of arterial oxygenation all laboratory testing is left up to the discretion of the healthcare provider. Patients in risk class I or II can be safely cared for at home. Risk class III can generally be cared for at home, but an inpatient observation is reasonable. Patients in risk classes IV and V should be admitted to the hospital (table 1.4). All CAP patients with unexplained or a high degree of hypoxemia should be admitted to the hospital. Clinical judgment should supersede the recommendations of clinical prediction rules.

    Key principles of pharmacotherapy for CAP include the following: (1) once the diagnosis is established, delays in administering antibiotics are associated with increased mortality; (2) all patients with CAP should be covered for “atypical” pathogens; and (3) recent antibiotic exposure should be considered when choosing empirical antibiotics. Clinicians should seek specific environmental exposures that may suggest an unusual pathogen (table 1.5).

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