Effects of particulate air pollution on tuberculosis development in seven major cities of Korea from 2010 to 2016: methodological considerations involving long-term exposure and time lag

OBJECTIVES: Epidemiological evidence of associations between ambient particulate matter (PM) and tuberculosis (TB) risk is accumulating. Two previous studies in Korea found associations between air pollution-especially sulfur dioxide (SO2)-and TB. In this study, we conducted an annual time-series cross-sectional study to assess the effect of PM with an aerodynamic diameter less than 10 mu m (PM10) on TB risk in seven major cities of Korea from 2010 to 2016, taking into account time lag and long-term cumulative exposure. METHODS: Age-standardized TB notification rates were derived using the Korea National TB Surveillance System. Annual average PM10 concentrations were obtained from annual Korean air quality reports. We applied a generalized linear mixed model with unconstrained distributed lags of exposure to PM10. We adjusted for potential confounders such as age, health behaviors, and area-level characteristics. RESULTS: Both average annual PM10 concentrations and age-standardized TB notification rates decreased over time. The association between cumulative exposure to PM10 and TB incidence became stronger as a longer exposure duration was considered. An increase of one standard deviation (5.63 mu g/m(3)) in PM10 exposure for six years was associated with a 1.20 (95% confidence interval, 1.17 to 1.22) times higher TB notification rate. The marginal association of exposure duration with the TB notification rate was highest at four and five years prior to TB notification. This association remained consistent even after adjusting it for exposure to SO2. CONCLUSIONS: The findings of this study suggest that cumulative exposure to PM10 may affect TB risk, with a potential lag effect.