Association between emergency admission for peptic ulcer bleeding and air pollution: a case-crossover analysis in Hong Kong's elderly population

Background Air pollution increases intestinal permeability, alters the gut microbiome, and promotes inflammation, which might contribute towards gastrointestinal bleeding. In the present study, we aim to examine whether shortterm elevations in air pollution are associated with increased numbers of emergency hospital admissions for peptic ulcer bleeding in Hong Kong. Methods Daily air pollution (particulate matter with aerodynamic diameter less than 2.5 mu m [PM2.5], nitric oxide [NO2], sulpher dioxide [SO2], and ozone [O-3]) data during 2005-10 were collected from the Environmental Protection Department and emergency admission data for peptic ulcer bleeding in elderly people (aged 65 years or older) from the Hospital Authority of Hong Kong. A time stratified case-crossover analysis with conditional logistic regression was used to estimate the excess risk of peptic ulcer bleeding associated with each air pollutant, in single-pollutant and multi-pollutant models. Cardiorespiratory diseases were used as positive controls. Findings 8566 emergency admissions for peptic ulcer bleeding were recorded among Hong Kong's elderly population during 2005-10; the daily number of admissions ranged from 0 to 13. An IQR increment of 5-day moving average (lag(04)) of NO2 concentration (25.8 mu g/m(3)) was associated with a 7.6% (95% CI 2.2-13.2) increase in emergency admissions for peptic ulcer bleeding. Multi-pollutant models confirmed the robustness of the risk estimates for NO2. Other pollutants (PM2.5, SO2, and O-3) were not associated with peptic ulcer bleeding admissions. Interpretation Short-term elevation in ambient NO2 might trigger peptic ulcer bleeding events and increase the risk of emergency admissions for peptic ulcer bleeding in Hong Kong's elderly population. These findings strengthen the hypothesis that air pollution affects not just cardiopulmonary diseases, but also certain diseases of the digestive system. Copyright (C) The Author(s). Published by Elsevier Ltd.