Identifying Cough Trajectories to Predict Asthma Outcomes: Insights from Growth Based Trajectory Modelling and Generalized Estimating Equations

Background: Coughing is common in early childhood. While often benign, cough could be an early sign of chronic pediatric conditions, such as asthma, which are associated with adverse long-term effects. Therefore, understanding the temporal pattern of coughing is essential to inform timely prevention, diagnosis, and treatment. Objectives: This study aimed to identify distinct cough trajectories from infancy (3 months) to preschool (up to 5 years of age) using parent-reported data from 3,454 children in the CHILD Cohort Study. We then examined how these patterns relate to health outcomes and healthcare-seeking behaviours. Methods: Group-based trajectory modeling (GBTM) was applied to classify participants into latent subgroups with similar cough trajectories. Model selection was based on BIC, AIC, posterior probabilities, and clinical interpretability. Generalized Estimating Equations (GEE) were subsequently used to assess associations between cough trajectories and respiratory morbidity, including asthma, unscheduled doctor visits, emergency department/hospital visits, and medication use. Results: A three-group model, including never/infrequent, early-onset, and late-onset cough, was selected based on the lowest BIC and AIC values, with median posterior probabilities exceeding 70%. Using GEEs, we found that membership in the late-onset cough trajectory was significantly associated with increased risk of unscheduled doctor visits and bronchodilator use by preschool, after adjusting for confounders. No significant associations were observed between early-onset cough and respiratory outcomes after confounder adjustment. Conclusions: Late-onset cough (starting at 3-4 years) was associated with increased bronchodilator use and primary healthcare utilization, suggesting it may be an early marker of respiratory vulnerability. These findings underscore the importance of cough and its timing in identifying children at risk for persistent respiratory morbidity.