Modifiable risk factors for acute respiratory tract infections in infants: evidence from a cohort study in Southern Thailand.

Acute respiratory tract infections (ARIs) are a major contributor to infant morbidity globally. We aimed to identify modifiable behavioral risk factors for ARI among infants in a tropical, resource-limited setting. This prospective cohort study enrolled healthy term infants (∼2 months old) at Songklanagarind Hospital. The primary exposures included four modifiable factors during the first 6 months of life: exclusive breastfeeding, bottle-feeding, pacifier usage, and passive smoking. We used multiple Poisson regression models to identify factors associated with the frequency of ARI between 6 and 12 months of age. A cohort of 671 infants was enrolled, of whom 271 (40.3%) experienced at least one episode of ARI between 6 and 12 months of age, with the majority (69.7%) experiencing only one episode. Infants who were bottle-fed during the first 6 months of life had a higher risk of ARI compared with those who were not [incidence rate ratio (IRR) = 1.37, 95% confidence interval (CI): 1.05-1.82, P = .025], and the risk increased with longer duration of bottle use. A similar trend was observed with pacifier use, which was associated with an increased risk of ARI (IRR = 1.33, 95% CI: 1.02-1.71, P = .031). While most participants were breastfed and exposed to passive smoking during the first 6 months, no significant associations with ARI were identified. Bottle-feeding and pacifier use were associated with 37% and 33% increases in risk of ARI, respectively. These findings can inform child health supervision and preventive care guidelines.