The COVID-19 pandemic drastically altered human behaviors alongside meteorological and environmental conditions, yet how these shifts differentially impacted respiratory versus intestinal infectious diseases remains unclear. This study investigates the evolving relationships between environmental exposures and disease transmission across pre-pandemic, pandemic, and post-pandemic phases. We analyzed surveillance data for notifiable respiratory and intestinal diseases in Sichuan Province (2006–2023), integrating meteorological and environmental pollution data via principal component analysis (PCA). A modeling framework combining PCA with generalized additive distributed lag non-linear models (PCA-GAM-DLNM) was applied to quantify the non-linear and lagged effects of composite environmental exposures on disease risks. A significant divergence emerged during the pandemic: respiratory diseases declined sharply due to non-pharmaceutical interventions (NPIs), whereas intestinal diseases (e.g., infectious diarrhea) remained stable or increased, correlating with worsened water pollution indicators despite improved air quality. We identified four distinct exposure–lag patterns, ranging from immediate effects (acute hemorrhagic conjunctivitis) to protection–risk reversal effects (mumps). Simulations indicated that using medium-to-high exposure levels as baselines yields more reliable early warnings than average levels. Respiratory and intestinal diseases exhibit differential environmental sensitivities. The persistence of intestinal diseases during the pandemic suggests that NPIs targeting airborne transmission are insufficient for waterborne risks. Future public health strategies require integrated management coordinating air and water quality control, with targeted interventions accounting for specific disease lag mechanisms and extreme weather risks.
Yang et al. (Thu,) studied this question.