Hospital Admissions and Fine Particulate Air Pollution

To the Editor: Dr Dominici and colleagues provided evidence of significant adverse health effects that can occur from exposure to air pollution with ambient levels of fine particles (particulate matter of 2.5 μm in aerodynamic diameter [PM2.5]) in a large nationwide sample of older adults. The breadth and size of their Medicare study population, and the recent Environmental Protection Agency (EPA) proposal for new legal limits for this air pollutant, raise a timecritical question: can this same study population be used to further test the hypothesis that the EPA proposal to set a maximum daily exposure limit of 35 μg/m will be sufficient to eliminate these adverse health effects? It would be highly informative if the authors could conduct subset analyses to test whether this newly proposed air pollution standard, if achieved, could actually eliminate the public health risk of excess hospital admissions from acute exposures to PM2.5 air pollution in this population.