Editor’s Note: Dr. Claire Castellano (she/her/hers) is a resident physician in pediatrics at the Children’s Hospital of Philadelphia. In addition to her M.D., Claire has a Master’s in Public Health, focusing on global epidemiology. Claire hopes to combine her interests in medical education and global health in her career as a pediatrician. -Rachel Y. Moon, MD, Associate Editor, Digital Media, Pediatrics
Approximately 200,000 infants younger than 90 days are evaluated for fever annually. In the recently updated practice guidelines from the American Academy of Pediatrics (AAP) regarding diagnostic testing for febrile infants 8–60 days old, they noted that virus-positive febrile infants have lower rates of urinary tract infections (UTIs) and invasive bacterial infections (IBIs), including bacteremia and bacterial meningitis, compared to virus-negative febrile infants.
However, for febrile infants 61–90 days old, there are limited data on the rates of UTIs and IBIs and no AAP practice guideline. Dr. Paul Aronson from Yale School of Medicine and colleagues from the Pediatric Emergency Care Applied Research Network (PECARN) Registry Working Group analyze the prevalence of UTIs and IBIs in 61-90-day-old infants with fever in their article and accompanying video abstract, “Risk of Bacterial Infections in Febrile Infants 61–90 Days Old with Respiratory Viruses,” being released early in Pediatrics this week (10.1542/peds.2025-070617).
The authors analyzed 2012–2024 data from a retrospective cohort in the PECARN registry.
Infants were included if they had:
- Documented temperature > 38o C
- At least one respiratory virus test obtained
- Either urinalysis and/or blood culture obtained
Of 3690 febrile infants aged 61–90 days who met all study criteria, 46.9% were positive for at least one respiratory virus.
Compared to virus-negative infants, virus-positive infants had:
- Lower prevalence of UTIs (4.4% versus. 12.5%)
- Lower prevalence of IBIs (0% versus. 3.3%)
- Lower prevalence of bacteremia without meningitis (1.0% versus. 3.0%)
- Lower prevalence of bacterial meningitis (0 cases versus. 4 cases)
Of note, of 11 virus-positive infants with bacteremia, 6 also had a UTI.
Subgroup analysis specifically examined SARS-CoV-2, RSV, influenza, and rhinovirus, as these are common causes of viral infections often tested in the ambulatory or emergency department setting. They found:
- UTIs were less prevalent in SARS-CoV-2-, RSV-, or influenza-positive infants.
- Bacteremia was less prevalent in SARS-CoV-2-positive infants
- RSV-positivity or influenza-positivity did not decrease prevalence of bacteremia.
- UTIs and bacteremia were similar in prevalence among rhinovirus-positive and rhinovirus-negative infants.
In summary, in respiratory virus–positive infants 61–90 days old, IBIs are significantly less prevalent. While UTIs are less common in these respiratory virus-positive infants, the decrease is not significant. These results can help guide diagnostic testing for this group:
- CSF testing is likely unnecessary in virus-positive infants: no cases of meningitis in 12 years of study data.
- Blood work testing can be based on shared decision-making and on specific viral positivity: fewer cases of bacteremia in COVID-positive infants and more cases in rhinovirus-positive infants.
- Urine testing should remain in the routine work-up: around 4% of virus-positive infants also had a UTI.
Dr. Kathryn Hunt and Dr. Lisa Nigrovic of Boston Children’s Hospital reflect on these findings in their commentary, “Considering a Viral Swab for Febrile Infants 61 to 90 Days of Age” (10.1542/peds.2025-071360). They note that clinical assessment, including duration of fever, maximum temperature, and associated exam findings, are absent in the PECARN dataset but often guide diagnostic testing decisions. However, until more clinical data can be collected, the Aronson study’s findings can help inform clinician’s approach to diagnostic testing for infants in the third month of life.
