Bacterial

Abstract
Importance The prevalence of invasive bacterial infections (IBIs), specifically bacteremia and bacterial meningitis, is not well established among febrile infants in the third month of life. International guidelines exclude or vary in management recommendations for this age group.

Objective To assess the prevalence of IBIs among febrile infants aged 60 to 90 days.

Data Sources MEDLINE, Embase, the Cochrane Central Register of Controlled Trials, and Scopus were searched with deliberate limitation to studies between January 1, 2000, to October 2, 2025, and analyzed in December 2025.

Study Selection Studies were included that reported on previously healthy, well-appearing febrile infants 60 to 90 days old evaluated in emergency department or outpatient settings and for whom patient-level IBI status could be ascertained.

Data Extraction and Synthesis Data were extracted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines, and risk of bias was assessed using the Joanna Briggs Institute critical appraisal Checklist for Prevalence Studies. Pooled prevalences were calculated using random-effects generalized linear mixed models of logit-transformed single proportions of cases.

Main Outcomes and Measures The primary outcome was the prevalence of IBI. Secondary outcomes included the prevalence of bacteremia and bacterial meningitis separately.

Results The search yielded 13 130 records; 59 studies were included (20 distinct datasets of 34 835 infants). The pooled prevalence of IBI was 1.11% (95% CI, 0.84%-1.47%), bacteremia was 1.01% (95% CI, 0.76%-1.34%), and bacterial meningitis was 0.11% (95% CI, 0.08%-0.16%). Results were consistent across multiple sensitivity analyses excluding (1) retrospective cohorts; (2) cohorts of only infants with fever without source; (3) cohorts with shorter clinical follow-up of less than 7 days; and (4) the largest study (66% of all included patients).

Conclusions and Relevance In this systematic review and meta-analysis, the pooled prevalence of IBI among well-appearing febrile infants in the third month of life was 1.11%; bacteremia accounted for most cases, whereas bacterial meningitis was rare. These contemporary prevalence estimates should inform guideline development and shared parent and clinician decision-making for the management of these infants.