Short-term exposure to ambient air pollutants and Herpes zoster risk: a nationwide case-crossover analysis.

Although herpes zoster (HZ) imposes a substantial burden in ageing populations, the environmental determinants of varicella zoster virus (VZV) reactivation remain poorly characterized. This study examined whether short-term exposure to ambient air pollution is associated with HZ incidence, while considering demographic and clinical effect modification. This nationwide time-stratified case-crossover study included 154,042 HZ-related hospital visits in South Korea between 2002 and 2019. Percent changes in HZ occurrence associated with particulate matter (PM10), sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3) were estimated using conditional logistic regression models adjusted for meteorological factors. Short-term increases in ambient pollutants were associated with higher HZ incidence, with observed lagged effects for PM10 at lag 11 (+0.73%), SO2 (+1.28%) and NO2 (+1.55%) at lag 12, CO at lag 14 (+1.44%), and O3 at lag 5 (+1.76%). Subgroup analyses suggested more pronounced associations among adults aged ≥50 years, socioeconomically disadvantaged groups, and non-metropolitan residents than among their counterparts, indicating potential variations in susceptibility. Our findings suggest that acute exposure to ambient air pollutants might be associated with VZV reactivation, particularly among vulnerable populations. While further research is needed to establish causality, these results provide preliminary evidence that air quality may be a relevant environmental factor to consider in the context of HZ risk management.