The influence of the severity of community-acquired pneumonia on the usefulness of blood cultures

The value of blood cultures;in community-acquired pneumonia (CAP) has been questioned. At issue is the potential for blood cultures to change manageme nt. We prospectively studied the yield and impact of blood cultures in pati ents admitted with CAP. Two hundred and nine subjects had at least two bloo d cultures prior to receiving antibiotics. The severity of CAP was graded u sing the Pneumonia Severity Index(PSI). Twenty-nine patients (13.9%) had a pathogen identified by blood culture. The yield of blood cultures increased with PSI grade (I-5.3%, II-10.2%, III-10.3%, IV-16.1%, V-26.7%), as did th e likelihood of blood cultures changing antibiotic therapy (I to III 0%, IV -9.7%, V-20.0%). One hundred and seventy-nine (85.6%) patients received a q uinolone, limiting the impact of pathogens resistant to p-lactams. Four of 16 patients (25.0%) with a culture (blood or sputum)-guided change in antib iotic therapy died, compared to five of 31 patients (16.1%) who had an empi ric change. Blood cultures are of minimal value in mild to moderate CAP, an d should be limited to patients with PSI grade IV or V CAP unless a specifi c risk factor for pathogens resistant to the empiric therapy is present.