Coarse particulate matter associated with increased risk of emergency hospital admissions for pneumonia in Hong Kong

Background Epidemiological research on the effects of coarse particles (PMc, particulate matter between 2.5 and 10 mu m in aerodynamic diameter) on respiratory morbidity is sparse and inconclusive. Pneumonia is an inflammatory condition of lung caused by infections, which may be triggered and exacerbated by PMc exposure. Aim To estimate the effect of PMc on emergency hospital admissions for pneumonia after controlling for PM2.5 and gaseous pollutants. Method PMc concentrations were estimated by subtracting PM2.5 from PM10 measurements in each of the 10 air monitoring stations from January 2011 to December 2012 in Hong Kong and then citywide daily average concentrations of PMc were computed from the 10 stations. Generalised additive Poisson models were used to examine the relationship between PMc and daily emergency hospital admissions for pneumonia, adjusting for PM2.5 and gaseous pollutants (NO2, SO2 and O-3). Subgroup analyses by gender and age were also performed to identify the most susceptible subpopulations. Results PMc and PM2.5 were significantly associated with emergency pneumonia hospitalisations. Every 10 mu g/m(3) increment of PMc in the past 4 days (lag(0)-lag(3)) was associated with a 3.33% (95% CI 1.54% to 5.15%) increase in emergency hospitalisations for pneumonia. The effect estimates of PMc were robust to the adjustment of PM2.5, NO2 or SO2, but attenuated on the inclusion of O-3 in the model. Women, children and older people might be more vulnerable to PMc exposure. Conclusions Short-term PMc exposure is associated with emergency hospitalisations for pneumonia in Hong Kong. Air quality regulation specifically for PMc might be considered.