Bacterial coinfection in young febrile infants with SARS-CoV-2 infection.

We aimed to assess the prevalence of serious bacterial infections (SBIs) in febrile infants < 90 days of age with SARS-CoV-2 infection versus SARS-CoV-2-negative febrile infants. A retrospective cohort study was conducted in a tertiary pediatric emergency department between March 2020 and October 2022. Febrile infants < 90 days of age who underwent SARS-CoV-2 testing were included. SBIs were defined as urinary tract infection (UTI), bacteremia, and/or bacterial meningitis; bacteremia and bacterial meningitis were considered invasive bacterial infections (IBIs). SBIs rates were compared between SARS-CoV-2-positive and negative infants and stratified by age. We included 779 infants: 221 (28.4%) SARS-CoV-2-positive and 558 (71.6%) SARS-CoV-2-negative. The SBI rate in the SARS-CoV-2-positive group was 5.9% vs 22.9% in the SARS-CoV-2-negative group (p < 0.001; relative risk (RR) 0.26; [95% CI 0.15-0.44]); the most common infections were UTI (5.4% vs 22.0%; p < 0.001). The IBI rate was 0.5% in the SARS-CoV-2-positive group vs. 3.2% in the negative group (p = 0.024; RR 0.14 [95% CI 0.02-1.04]). There were no cases of bacterial meningitis in the positive infants. SARS-CoV-2-positive infants > 28 days of age had a decreased likelihood of SBI (RR 0.22 [95% CI 0.11-0.43]), with no cases of IBI identified.     Conclusions: Febrile infants < 90 days of age with SARS-CoV-2 infection are at significantly lower risk of SBIs than those who are SARS-CoV-2-negative. Nevertheless, the rate of UTI remains considerable in SARS-CoV-2-positive infants. SARS-CoV-2 detection may be relevant in considering IBI risk for well-appearing febrile infants 29-89 days of age. What is Known: • Febrile infants with laboratory-confirmed viral infections have a significantly lower risk of serious bacterial infections when compared to those without them. Data focusing on very young febrile infants with a SARS-CoV-2 infection is still limited. What is New: • Young febrile infants with SARS-CoV-2 infection are at significantly lower risk of serious bacterial infections than those who are SARS-CoV-2-negative. Nevertheless, the rate of urinary tract infection remains considerable. SARS-CoV-2 detection may be relevant in considering invasive bacterial infection risk for well-appearing febrile infants 29-89 days of age.