Demographic data, medical history, medication use, and physical findings on admission were collected by review of the emergency department and admission notes by study personnel (A.R.F. and Y.M.), and data were recorded on standardized forms. Laboratory data collected included admission white blood cell count, blood and sputum bacterial culture results, and chest radiograph (CXR) readings within 72 hours of admission. In those patients in whom multiple CXRs were obtained in the 72-hour period, all abnormal readings were recorded. Hospital length of stay, intensive care use, days of antibiotics in the hospital, discharge medications, and deaths were also recorded. The primary investigator (A.R.F.) reviewed medical records to determine if influenza or viral infection was included in the differential diagnosis of the admitting health care providers (physicians, nurse practitioners, or physician assistants), as evidenced by a statement in a written note or an order for influenza testing. Records were examined for evidence that the influenza test result was known and to determine if a specific change in management was undertaken in response to that information (ie, add antiviral agent, discontinue or change antibiotic agent, or hospital discharge). Medical records were further reviewed for complications possibly related to antibiotics (diarrhea, drug rash, fungal infection, or renal, hepatic, or bone marrow dysfunction). The study was approved by the University of Rochester research subjects review board and the Rochester General Hospital clinical investigation committee.