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The Common Febrile Infant and the Common Cold :

January 18, 2018

The well-appearing febrile infant is perhaps one of the most well-studied well-appearing populations in pediatrics. The reason?

The well-appearing febrile infant is perhaps one of the most well-studied well-appearing populations in pediatrics. The reason? Fever may be the only presenting symptom in this population before becoming not-so-well-appearing.  Certainly, not all infants with a fever will have life-threatening invasive bacterial infections (IBI)—but approximately 10% do, and it’s important to identify these infants quickly to provide appropriate treatment.  But how do we identify these at-risk infants, particularly when the vast majority of febrile well-appearing infants aged 1-90 days have viral illnesses?  Previous studies have reported the potential for positive rapid respiratory syncytial virus and influenza testing to guide a more limited evaluation for infants at low-risk for IBIs.  However, a knowledge gap still exists between the risk for IBIs and infants testing positive for human rhinovirus (HRV).

In this month’s Pediatrics, Blaschke et. al. (10.1542/peds.2017-2384) share results from a retrospective observational study of 4,037 children receiving respiratory viral testing by multiplex polymerase chain reaction (RVPCR).  Patients were cared for within the Intermountain Health Care system providing care for more than 90% of Utah infants and included a variety of settings including a tertiary pediatric referral center, regional medical centers, and community hospitals.  The primary objective of this study was to evaluate the frequency of IBIs (urinary tract infections [UTI], bloodstream infections [BSI], or meningitis) in well-appearing febrile infants with HRV, non-HRV respiratory viruses, and infants with no respiratory virus detected via RVPCR.  HRV was the most common detected respiratory virus and was found alone in 35% of RVPCR-positive infants.  Overall, IBIs were detected in nearly 10% of infants with positive RVPCR testing.  When study authors stratified both by age (1-28 days versus 29-90 days) and type of IBI, the results got interesting.  HRV detection in infants aged 1-28 days was associated with a statistically decreased risk of IBI (RR 0.41; 95% CI 0.19-0.88), however this result seems largely driven by a reduction in UTIs as the change in risk of bloodstream infection was not statistically significant when assessed alone.  In infants aged 29-90 days, the reduction in risk wasn’t as dramatic but the detection of HRV nonetheless resulted in a reduced risk for IBI (RR 0.52; 95% CI 0.34-0.80). 

So, should a RVPCR positive for HRV change your diagnostic and management approach to the well-appearing infants?  Perhaps—but it would likely depend on the age of the infant.  Study authors acknowledge that, while infants aged 1-28 days had a lower risk of IBI overall, there was no significant difference in the prevalence of bloodstream infections.  Moreover, no cases of meningitis were identified, preventing the authors from assessing any change in risk as it relates to HRV detection.  As such, Blaschke et. al. concluded that the study provides no evidence to risk-stratify infants in this age group.   However, in infants aged 29-90 days, the overall risk of IBI as well as the risk for both UTI and blood stream infections were significantly reduced.  HRV detection in this age group could potentially be used to guide the extent of diagnostic evaluation and/or admission to the hospital.  See these results and additional conclusions from the study authors for yourself in this month’s Pediatrics!

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