Prenatal and childhood infections as risk factors for psychiatric disorders: A systematic review and meta-analysis.
OBJECTIVES To perform a systematic review and meta-analysis of the associations between infections during the prenatal period or childhood and the risk of subsequent psychiatric disorders (including ADHD, ASD, internalising and psychotic disorders) considering timing (prenatal and childhood), type (bacterial vs viral), and trimester of infection. METHODS A systematic search of PubMed and ProQuest was conducted from 20 May 2024-15 July 2025 for cohort studies reporting psychiatric outcomes following infection exposure during pregnancy or childhood (0≤12 years). Study quality was assessed using the STROBE checklist. Where possible, random-effects meta-analyses were conducted using logarithmic risk ratios with 95% confidence intervals. RESULTS Seventy-five studies were included in the review, with 59 contributing to meta-analyses. Prenatal infection was associated with increased risk of ADHD (RR = 1.18; 95% CI: 1.07-1.31), ASD (RR = 1.17; 95% CI: 1.07-1.28), and psychotic disorders (RR = 1.21; 95% CI: 1.13-1.29). Childhood infection was also associated with ADHD (RR = 1.45; 95% CI: 1.27-1.66), ASD (RR = 1.41; 95% CI: 1.26-1.59), and psychosis (RR = 1.31; 95% CI: 1.07-1.60). Subgroup analyses indicated prenatal bacterial infections were associated with ADHD and ASD, while prenatal viral infections; particularly during the first-trimester, were linked to psychotic disorders. Childhood bacterial infections were also associated with ADHD and ASD. Too few studies were available to conduct meta-analyses for internalising disorders. CONCLUSION Early-life infection is associated with increased risk of multiple psychiatric outcomes. These findings support a role for immune activation during critical developmental periods in shaping later psychiatric risk.