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 μm 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 PM(2.5) and gaseous pollutants.

Method: PMc concentrations were estimated by subtracting PM(2.5) from PM(10) 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 PM(2.5) and gaseous pollutants (NO(2), SO(2) and O(3)). Subgroup analyses by gender and age were also performed to identify the most susceptible subpopulations.

Results: PMc and PM(2.5) were significantly associated with emergency pneumonia hospitalisations. Every 10 μg/m(3) increment of PMc in the past 4 days (lag0-lag3) 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 PM(2.5), NO(2) or SO(2), 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.