So for most kids, you get a fever, and maybe it lets you stay home from school. But in a small infant, it’s panic inducing. That’s because there’s a small, but greater than zero chance that a baby has a serious bacterial infection that could kill it without treatment.
When I was an intern, any infant under 2 months of age got rushed to the hospital. Then we drew blood for a CBC and blood culture. We stuck a catheter into their bladder to get urine for a urinalysis and urine culture. Then we stuck a needle into their back to obtain spinal fluid to check for cells and do a CSF culture.
Every infant. Every fever.
And then we put them in the hospital for 48 hours or more until every single culture came back negative. You have to wait, because you don’t get a “negative result”. You just get nothing growing. That’s a negative. But how long do you wait?
When it’s called a “negative”, we send you home. I can remember no children who were otherwise well appearing who wound up having a positive culture. But it can happen. So we play it safe.
As you can imagine, this costs money. It disrupts families. It leaves infants exposed to other illnesses in the hospital. It just plain sucks. By the time I was a fellow, we were trying to develop new guidelines by which we could send some older infants home on antibiotics and follow them from there. But it still sucks.
So I was happy to see this paper, “Blood Culture Time to Positivity in Febrile Infants With Bacteremia“:
Importance: Blood cultures are often obtained as part of the evaluation of infants with fever and these infants are typically observed until their cultures are determined to have no growth. However, the time to positivity of blood culture results in this population is not known.
Objective: To determine the time to positivity of blood culture results in febrile infants admitted to a general inpatient unit.
Design, Setting, and Participants: Multicenter, retrospective, cross-sectional evaluation of blood culture time to positivity. Data were collected by community and academic hospital systems associated with the Pediatric Research in Inpatient Settings Network. The study included febrile infants 90 days of age or younger with bacteremia and without surgical histories outside of an intensive care unit.
Exposure:s Blood culture growing pathogenic bacteria.
Main Outcomes and Measures: Time to positivity and proportion of positive blood culture results that become positive more than 24 hours after placement in the analyzer.
Results: A total of 392 pathogenic blood cultures were included from 17 hospital systems across the United States. The mean (SD) time to positivity was 15.41 (8.30) hours. By 24 hours, 91% (95% CI, 88-93) had turned positive. By 36 and 48 hours, 96% (95% CI, 95-98) and 99% (95% CI, 97-100) had become positive, respectively.
Conclusions and Relevance: Most pathogens in febrile, bacteremic infants 90 days of age or younger hospitalized on a general inpatient unit will be identified within 24 hours of collection. These data suggest that inpatient observation of febrile infants for more than 24 hours may be unnecessary in most infants.
They looked at data on 17, yes seventeen, different hospital systems for between 2 and 6 years. And in all that time, they found only 392 blood cultures from non-ICU or inpatient settings that were positive with pathogens. So this ain’t common. More important, when they were positive, they were found to be so within 15 hours on average. More than 90% of them were positive in a day.
In other words, we can probably make a judgement call earlier. If nothing grows by 24 hours, and a baby looks well, you can probably go home with strict instructions. This may not sound like a big deal to you, but it would be a huge deal for the doctors caring for these babies, and – much more importantly – the families who just want to get home and be with their newborns.
