Moderate-to-late preterm birth, common respiratory pathogens, and severe lower respiratory tract infections across childhood

Purpose Children born moderate-to-late preterm (MLP; 32 to < 37 weeks) are at increased risk of respiratory morbidity. We aimed to evaluated the association between MLP birth and lower respiratory tract infections (LRTIs) severity across age groups, and characterized biological interactions between MLP status and respiratory pathogens. Methods : This 11-year retrospective study included children hospitalized with LRTIs at Tongji Hospital, Wuhan. The primary outcome was a composite clinical severity measure. Stratified analyses were performed across infancy, early childhood, and middle childhood/early adolescence using multivariable logistic regression. Propensity score matching balanced covariates to compare pathogen positivity rates. Additive interactions were quantified via relative excess risk due to interaction (RERI) and attributable proportion (AP). Results : Of 65,859 patients, 1,453 (2.21%) were born MLP. MLP birth independently predicted increased risk of composite severity outcomes across all age groups ( p for interaction = 0.868), with adjusted odds ratios of 1.16 (95% CI: 0.99, 1.34) in infants, 1.27 (95% CI: 1.03, 1.56) in early childhood, and 1.71 (95% CI: 1.21, 2.41) in middle childhood/early adolescence. Matched pathogen positivity rates were comparable between full-term and MLP children. Notably, a significant synergistic additive interaction was identified between MLP status and respiratory syncytial virus (RSV) infection (RERI = 1.16, 95% CI: 0.30, 2.35; AP = 0.43, 95% CI: 0.11, 0.57). Conclusion : MLP birth confers a persistent predisposition to severe LRTI outcomes that extends beyond infancy into early and middle childhood. Although MLP birth does not alter susceptibility to microbial acquisition, it distinctively amplifies severe outcomes when it co-occurs with RSV infection.