PM2·5 concentration and elderly tuberculosis: analysis of spatial and temporal associations

Abstract

BackgroundChina periodically has severe ambient particulate matter (PM) pollution, which could cause compromised pulmonary immunity in the population and result in high cardio-respiratory morbidity and mortality. Acknowledging the highly prevalent latent tuberculosis in elderly people, we hypothesise that they are more prone to tuberculosis reactivation in the presence of air pollution. MethodsWe examined the spatial and temporal association between PM2·5 concentration and the number of reported cases of tuberculosis in elderly people aged 65 years and older in Hong Kong. Tuberculosis notification data in 2005–07 were collected from the Chinese Government's TB and Chest Service. Monthly and annual PM2·5 concentration by geographical subdistrict (DCCA) for the corresponding years were derived from satellite images. Age–gender standardised notification rate (SNR) of tuberculosis cases in elderly people was calculated per DCCA/time. Their temporal association with PM2·5 was examined by dynamic linear regression in R, and spatial association by spatial regression in GeoDa. FindingsAmong 17 294 new cases of tuberculosis reported in 2005–07, 6879 (40%) cases were in elderly people (2·69 men for every woman). The mean monthly SNR for elderly men was 35·4 per 100 000 persons (range 25·2–45·3), and the mean of mean PM2·5 in DCCA was 30·5 μg/m3 (16·1–47·1). Temporally, the SNR for elderly men was associated with PM2·5 in lag 0, lag −1 (ie, moving PM2·5 1 month earlier), and lag −4 to −6 months, with the most significant positive association at lag −6 months. However, no temporal association between the SNR for elderly women and PM2·5 was observed. Spatially, the SNR was associated with PM2·5 for elderly men in all 3 years but only for women in 2005. InterpretationWe detected spatial and temporal associations between cases of tuberculosis in elderly men and PM2·5. Tuberculosis reactivation might have occurred after exposure to high PM2·5 in the environment, as inferred from the lag interval of 6 months revealed in our results. The discrepancy between sexes and the effects of potential confounders such as sunshine duration, income level, and locality would need to be further investigated. FundingResearch Grants Council under Theme-based Research Scheme (T32-102/14N).