Little is known about the effect of air pollution on the gastrointestinal system. We studied the association between long-term exposures to outdoor PM2.5 and hospitalization for peptic ulcer diseases (PUD) in a large cohort of 66,820 Hong Kong Chinese elderly (aged ≥65). PM2.5 exposure at residence of individuals were estimated by satellite data through linkage with address details including floor level. Hospital admission records of the participants up to December 31, 2010 were retrieved from the central database of Hospital Authority. Cox regression was used to estimate the hazard ratio for PUD hospitalization associated with PM2.5 exposures. During the follow-up period, 1991 (3.3%) subjects had been hospitalized for PUD. It was found that PM2.5 exposure was associated with PUD hospitalization. Further analysis showed that the associations were significant for gastric ulcers but not for duodenal ulcers. The mechanism underlying the PM2.5 in the development of gastric ulcers warrants further research.

In Asia where air quality is poor and deteriorating, there is very little local data on the long-term effects of PM2.5. The limited number of studies done suggested it can be an important cause of morbidity and mortality. This cohort study was done 1998-2001 and consisted of 66,820 participants >65 years of age who were enrolled and interviewed in 18 Elderly Centers of the Department of Health, Hong Kong. All residential addresses were geocoded and the U.S. NASA satellite data were used for proxy exposure estimates to PM2.5. Cox regression models were used to calculate hazard ratios of mortality associated with PM2.5. Results suggested that in Hong Kong, exposure to PM2.5 was associated with mortality from natural causes, cardiovascular causes, ischemic heart disease, cerebrovascular disease and respiratory causes. This study proved that NASA satellite data can be a readily accessible and affordable approach to estimate a sufficient range of PM2.5 in any single city.

Interactions between temperature and PM_2.5 on mortality have not been well studied. Hence this study aimed at assessing the modification of temperature on the association between PM2.5 and cause specific mortality, by stratifying temperature into low, medium and high stratum in Hong Kong. Data retrieved from 1999-2011 were used for the study. Results showed a statistically significant interaction of PM2.5 and temperature between low and high temperature stratum for all natural mortality and mortality. Mortality effects of PM2.5 were stronger in low temperature stratum as oppose to those in high temperature stratum. In conclusion, temperature might modify mortality effects of PM2.5.