Diagnosis

Immunocompetent patients MUST have an infiltrate on chest radiograph to meet diagnostic criteria for pneumonia.

Sputum and blood cultures should be sent on all patients admitted to the hospital BEFORE initiating antibiotics, however...

Therapy should not be delayed if a sputum culture cannot be obtained.

The Legionella urine antigen is the test of choice for diagnosing legionella infection. However, this test detects only L. pneumophila serogroup 1, which is responsible for ~70% of infections. The turnaround time is ~24 hours (48 hours on the weekends).

HIV test should be obtained in all patients, but especially if age < 55, severe CAP, homeless, or other epidemiologic risk factors.