Incidence of asthma among preschool children in Suzhou, China: a large hospital-linked retrospective birth cohort study

Background Asthma remains an important global concern in children, with the preschool stage representing a critical period for susceptibility, identification, and treatment. We aimed to estimate the incidence of asthma among preschool children and to characterize its patterns. Methods We conducted a large hospital-linked retrospective birth cohort study including children born in 2017–2018 who received healthcare at Children’s Hospital of Soochow University. The outcome was the earliest physician-diagnosed asthma ascertained by screening citywide healthcare records in the Suzhou Municipal Health Information Center (SMHC) database. We estimated asthma incidence and exacerbation rates, and used a Poisson regression model to identify potential risk factors. Results The overall incidence rate of recorded physician-diagnosed asthma among preschool children was 21.3 per 1,000 person-years (PY), with a cumulative incidence of 11.8%. Sensitivity analyses using different asthma case definitions yielded cumulative incidence estimates ranging from 3.8% to 11.8%. The incidence was higher among children aged < 2 years than among those aged ≥ 2 years (33.5 vs. 14.8 per 1,000 PY, p < 0.001). Incidence for boys was higher than for girls, and this difference decreased with increasing age. Congenital heart disease (CHD), low birth weight (LBW), immunodeficiency (ID), and allergic diseases were associated with higher asthma incidence. Among children with asthma, exacerbation rates varied by age at diagnosis and time since diagnosis, with higher rates during the first year after diagnosis among children diagnosed at older ages. Conclusion This study provides real-world estimates of physician-diagnosed asthma among preschool children in Suzhou. Younger children, boys, and those with CHD, LBW, ID, or allergic conditions may warrant greater attention in asthma risk assessment and early monitoring, whereas children diagnosed with asthma at older ages may require closer follow-up due to higher exacerbation rates. Trial registration Not applicable.