Particulate Matter and Risk of Hospital Admission in the Kathmandu Valley, Nepal: A Case-Crossover Study.

Air pollution is known to lead to a substantial health burden, but the majority of evidence is based on data from North America and Europe. Despite rising pollution levels, very limited information is available for South Asia. We investigated the impact of particulate matter with an aerodynamic diameter less than or equal to 10 μm (PM10) on hospitalization, by cause and subpopulation, in the Kathmandu Valley, an understudied and rapidly urbanizing region in Nepal. Individual-level daily inpatient hospitalization data (2004-2007) were collected from each of 6 major hospitals, as Nepal has no central data collection system. Time-stratified case-crossover analysis was used with interaction terms for potential effect modifiers (e.g., age, sex, and socioeconomic status), with adjustment for day of the week and weather. Daily PM10 concentrations averaged 120 μg/m3, with the daily maximum reaching 403 μg/m3. A 10-μg/m3 increase in PM10 level was associated with increased risks of hospitalization of 1.00% (95% confidence interval (CI): 0.62, 1.38), 1.70% (95% CI: 0.18, 3.25), and 2.29% (95% CI: 0.18, 4.43) for total, respiratory, and cardiovascular admissions, respectively. We did not find strong evidence of effect modification by age, sex, or socioeconomic status. These results, in combination with the high levels of exposure, indicate a potentially serious human health burden from air pollution in the Kathmandu Valley.