The short effect of ambient temperature on childhood asthma and wheezing: a combination of a nested case-control study and a case-crossover study.

Although the incidence of childhood asthma and wheezing (AW) is increasing worldwide, the impact of ambient temperature on this is unclear. An infant birth cohort was established, and the children were followed up until two years of age. During this period, the exposure levels to atmospheric factors were individually evaluated on a daily basis as well as covariates information was collected. Both a nested case-control study and a case-crossover design were embedded to control for confounding bias and cross-validate the association between ambient temperature and childhood AW. A total of 5819 children in the birth cohort completed two years of follow-up, and 84 children were diagnosed with AW. The HRs for short-term high temperature on childhood AW were 1.659 (95% CI: 1.314, 2.095), 2.341 (95% CI: 1.712, 3.200), and 3.367 (95% CI: 1.987, 5.703) at a lag of 3, 2, and 1 days, respectively, by the distributed lag non-linear model based on the nested case-control study. The high temperature was further validated to be significantly associated with childhood AW during the 3 days before the onset, by the generalized additive model based on the case-crossover design.