High frequency of pseudobacteremia at a university hospital.

A prospective survey of all positive blood cultures was performed during a 6-month period at a 390-bed, tertiary-care teaching hospital in St Louis, Missouri. Data were collected from the clinical microbiology laboratory, medical records, and physicians caring for patients with positive blood cultures. Of 5,732 blood cultures, 261 (4.6%) were positive, and approximately half of these (51.3%) were categorized as false positive. Positive cultures were significantly more likely to be true positives if obtained from patients with malignancies or if they became positive within the first 48 hours of incubation.