Independent and joint effects of apparent temperature and ambient air pollution on endometriosis-related outpatient visits in Beijing, China: a time-series study

Endometriosis is a chronic gynecological disorder, and its symptom fluctuations and healthcare utilization may be influenced by environmental exposures. Although meteorological factors and air pollution have been associated with short-term health outcomes in a range of inflammation-related conditions, evidence on their nonlinear, lagged, and joint effects on endometriosis-related outpatient visits remains limited. In particular, the combined impact of apparent temperature and air pollution on endometriosis-related healthcare utilization has not been well characterized. In this time-series study, endometriosis-related outpatient visit records from Peking University First Hospital between January 1, 2022 and December 31, 2024 were linked with concurrent meteorological and air pollution data. A quasi-Poisson generalized additive model combined with a distributed lag nonlinear model was used to assess the nonlinear exposure-response relationships and lagged effects of apparent temperature and air pollutants on daily outpatient visits. Potential interactions were evaluated using stratified exposure-response analyses and additive interaction measures. Stratified analyses were further conducted by age group and season, with adjustment for long-term trend, seasonality, day of the week, and public holidays. A total of 39,015 endometriosis-related outpatient visits were included. Apparent temperature showed a nonlinear and delayed association with daily outpatient visits. Relative to the median apparent temperature (11.44℃), high apparent temperature (P90, 29.45℃) was associated with an increased cumulative relative risk over lag 0–14 days (RR = 1.126, 95% CI: 1.078–1.177). In the single-pollutant models, higher concentrations of PM 2.5 and PM 10 were associated with increased cumulative relative risks (PM 2.5 , lag 0–7: RR = 1.109, 95% CI: 1.044–1.177; PM 10 , lag 0–6: RR = 1.070, 95% CI: 1.014–1.128). A statistically significant positive additive interaction was observed between apparent temperature and ozone (interaction relative risk [IRR] = 1.114, 95% CI: 1.053–1.180). Apparent temperature and air pollution were associated with short-term fluctuations in endometriosis-related outpatient visits, and a positive additive interaction was observed between high apparent temperature and ozone. These findings highlight the potential importance of compound environmental exposures in shaping endometriosis-related healthcare demand under climate change and urban air pollution.