Time to detection of positive cultures in 28-to 90-day-old febrile infants

Objective. To determine the time to detection of positive blood, urine, and cerebrospinal fluid (CSF) cultures among febrile 28- to 90-day-old infants . Study Design. Retrospective cohort of consecutive 28- to 90-day-old infan ts presenting with a temperature of greater than or equal to 38 degrees C t o an urban pediatric emergency department. Positive cultures and times to d etection were noted. Patients were categorized as being at high risk for se rious bacterial illness (SBI) based on clinical and laboratory criteria. Results. Of the 3166 febrile infants seen in the emergency department durin g the study, 2733 had blood (86%), 2517 had urine (80%), and 2361 had CSF ( 75%) specimens obtained for culture, and 2190 had all 3 cultures (69%) sent . There were 224 positive cultures in 214 patients; of these, 191 had all 3 cultures (89%) sent. Subsequent analyses were confined to those who had al l 3 cultures sent. The detected rate of SBI was 8.7% (191/ 2190). There wer e 28 positive blood cultures (1.3%), 165 positive urine cultures (7.5%), an d 8 positive CSF cultures (.4%). Median time to detection of positive cultu res was 16 hours for blood, 16 hours for urine, and 18 hours for CSF. Four blood cultures (.1%), 20 urine cultures (.9%), and 0 CSF cultures were note d to have growth of a pathogen >24 hours after the specimen was obtained. A ll 4 blood cultures and 17 of 20 urine cultures with growth noted after 24 hours occurred among high-risk patients. Conclusions. The risk of identifying SBI after 24 hours is 1.1% among all 2 8- to 90-day-old febrile infants and .3% in low-risk infants.