Air pollution and admissions for acute lower respiratory infections in young children of Ho Chi Minh City

This study assessed the effects of exposure to air pollution on hospitalization for acute lower respiratory infection (ALRI) among children under 5 years of age in Ho Chi Minh City (HCMC) from 2003 to 2005. Case-crossover analyses with time-stratified selection of control periods were conducted using daily admissions for pneumonia and bronchiolitis and daily, citywide averages of PM10, NO2, SO2, and O-3 (8-h maximum average) estimated from the local air quality monitoring network. Increased concentrations of NO2 and SO2 were associated with increased admissions in the dry season (November to April), with excess risks of 8.50% (95%CI 0.80-16.79) and 5.85% (95%CI 0.44-11.55), respectively. PM10 could also be associated with increased admissions in the dry season, but high correlation between PM10 and NO2 (0.78) limits our ability to distinguish between PM10 and NO2 effects. In the rainy season (May-October), negative associations between pollutants and admissions were observed. Results of this first study of the health effects of air pollution in HCMC support the presence of an association between combustion-source pollution and increased ALRI admissions. ALRI admissions were generally positively associated with ambient levels of PM10, NO2, and SO2 during the dry season, but not the rainy season. Negative results in the rainy season could be driven by residual confounding present from May to October. Preliminary exploratory analyses suggested that seasonal differences in the prevalence of viral causes of ALRI could be driving the observed differences in effects by season.