Gestational age at birth and hospitalisations for infections among individuals aged 0–50 years in Norway: a longitudinal, register-based, cohort study

Summary Background Preterm birth is associated with increased risk of childhood infections. Whether this risk persists into adulthood is unknown and limited information is available on risk patterns across the full range of gestational ages. Methods In this longitudinal, register-based, cohort study, we linked individual-level data on all individuals born in Norway (January 01, 1967–December 31, 2016) to nationwide hospital data (January 01, 2008–December 31, 2017). Gestational age was categorised as 23–27, 28–31, 32–33, 34–36, 37–38, 39–41, and 42–44 completed weeks. The analyses were stratified by age at follow-up: 0–11 months and 1–5, 6–14, 15–29, and 30–50 years. The primary outcome was hospitalisation due to any infectious disease, with major infectious disease groups as secondary outcomes. Adjusted hospitalisation rate ratios (RRs) for any infection and infectious disease groups were estimated using negative binomial regression. Models were adjusted for year of birth, maternal age at birth, parity, and sex, and included an offset parameter adjusted for person-time at risk. Findings Among 2,695,830 individuals with 313,940 hospitalisations for infections, we found a pattern of higher hospitalisation risk in lower gestational age groups, which was the strongest in childhood but still evident in adulthood. Comparing those born very preterm (28–31) and late preterm (34–36) to full-term (39–41 weeks), RRs (95% confidence interval) for hospitalisation for any infectious disease at ages 1–5 were 3.3 (3.0–3.7) and 1.7 (1.6–1.8), respectively. At 30–50 years, the corresponding estimates were 1.4 (1.2–1.7) and 1.2 (1.1–1.3). The patterns were similar for the infectious disease groups, including bacterial and viral infections, respiratory tract infections (RTIs), and infections not attributable to RTIs. Interpretation Increasing risk of hospitalisations for infections in lower gestational age groups was most prominent in children but still evident in adolescents and adults. Possible mechanisms and groups that could benefit from vaccinations and other prevention strategies should be investigated. Funding 10.13039/501100011769 St. Olav’s University Hospital and 10.13039/100009123 Norwegian University of Science and Technology , 10.13039/501100005416 Norwegian Research Council , Liaison Committee for education, research and innovation in Central Norway , European Commission, Academy of Finland , 10.13039/501100006306 Sigrid Jusélius Foundation , 10.13039/501100005744 Foundation for Pediatric Research , and 10.13039/501100004325 Signe and Ane Gyllenberg Foundation .