1. The mean time to blood culture positivity in febrile infants with bacteremia was roughly 15 hours.
2. By 24 hours, 91% of blood cultures had already become positive. By 48 hours, 99% of blood cultures had become positive.
Evidence Rating Level: 2 (Good)
Study Rundown: Febrile infants often receive blood cultures routinely as part of their evaluation. These infants are often hospitalized for 48 hours or longer, receiving antibiotics while their blood culture results are pending. There is no standardized time interval of observation that has been recommended. This study demonstrated that most pathogens in febrile infants are identified on a blood culture within 24 hours, suggesting that hospitalization longer than 24 hours may be unnecessary.
Strengths of the study include a large number of hospitals that were included in the study, including a wide geographical area covering all major regions of the United States. Study limitations include the extensive exclusion criteria, which excluded a vast majority of positive blood cultures, including those from patients in intensive care units and patients who have had surgery. The time between blood culture collection and placement into the automated detection system was not considered in this study. Moreover, due to the cross sectional design of the study, patients were not followed up and their outcomes are not stated in the study.
Relevant Reading: Time to positivity of neonatal blood cultures: fast and furious?
In-Depth [cross sectional study]: This multicenter, retrospective, cross sectional study examined the blood culture results of febrile (>38.0 degrees C) infants 90 days old or younger, obtained from 17 hospital systems in the United States. Blood cultures were excluded if the infants were in an intensive care unit, had a surgical history, or if the organism was not treated as pathogenic. A total of 392 blood cultures were included in the study.
The mean time to positivity (TTP) was 15.41 hours (SD = 8.30). It was noted that TTP was shorter in cultures drawn from infants 30 days and younger as compared to infants 61 to 90 days old.. By 24 hours, 91% of cultures were positive. 96% and 99% of cultures were positive at 36 and 48 hours, respectively. E Coli species were the most prevalent (41%), followed by Group B streptococcal species (22%), viridans streptococci (8%), S aureus (6%), and Streptococcus pneumonia (5%). The TTP was not significantly different for different sexes. When common contaminating organisms were excluded, the TTP was not significantly affected.
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