The researchers reviewed blood culture reports of hospitalized patients from one academic medical center and two community hospitals in North Carolina. They then reviewed medical records of patients with positive blood cultures to learn about symptoms, signs, and sites of infection and medical conditions and treatments. They placed the patients into one of three groups (community-acquired, health care–associated, and nosocomial) and compared infection and patient characteristics across groups. The nosocomial group first had positive blood cultures at least 48 hours after hospitalization for another problem. The health care–associated group had positive blood cultures at the time of or within 48 hours of hospitalization and had recently needed complicated care (nursing home and dialysis patients, patients recently hospitalized, and patients recently given medicine in a vein [intravenous] at home). The community-acquired group first had positive blood cultures at the time of or within 48 hours of hospitalization but did not fit criteria for a health care–associated infection.