Preterm birth and the risk of respiratory syncytial virus hospitalisation in Australia’s Northern Territory: a population-based cohort study

The Northern Territory (NT) of Australia has high reported rates of both preterm birth and childhood respiratory syncytial virus (RSV) infections. The aim of this study was to investigate the association between preterm birth and risk of RSV-associated acute lower respiratory infection (RSV-ALRI) hospital admission among NT infants during their first year of life. A retrospective, population-based cohort study of NT mother-infant pairs from 2008 to 2017. Preterm birth was defined as gestation < 37 weeks. RSV-ALRI hospitalisations were identified using ICD-10-AM codes (J12.1, J20.5, J21.0, or J09-J22 plus B97.4). Risk of RSV-ALRI in preterm infants was assessed using generalised linear regression to calculate risk ratios (RR). A multivariable risk model adjusted for all available maternal, perinatal, and infant characteristics. Temporal trends in hospitalisation incidence were assessed using negative binomial regression. Overall, 10% (3839/39148) of infants were born preterm, and 2% (846/39148) were hospitalised with RSV-ALRI. Preterm infants (4%) had twice the risk of RSV-ALRI compared to term infants (2%) (risk ratio [RR] 2.26, 95% CI 1.90–2.69; adjusted RR 1.72, 95% CI 1.43–2.08), with the highest risk among those born < 32 weeks’ gestation (7%). Elevated risks were also observed in First Nations infants (4.5%), infants of young mothers aged < 19 years (4.9%), those living in very remote Central desert regions (7.1%), and infants of mothers who had a urinary tract infection during pregnancy (5.1%). The episode-based RSV-ALRI hospitalisation rate was 2.3 per 100 child-years, declining steadily across the decade of observation (incidence rate ratio [IRR] 0.90 per year, 95% CI 0.86–0.94). Preterm birth is an independent and significant risk factor for infant RSV hospitalisation in Australia’s NT. Other important risk factors include younger maternal age, residence in remote or Central desert regions, maternal urinary tract infection (UTI) during pregnancy, and male sex. RSV immunisation strategies will be crucial in protecting high-risk infants in the NT and elsewhere.