1. Exposure, Epidemiology, and Risk Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA
2. Channing Laboratory, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA
3. Department of Epidemiology and
4. Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts, USA
5. Pulmonary and Critical Care Medicine Section, Veterans Affairs Boston Healthcare System, Boston, Massachusetts, USA
6. School of Public Health, University of California–Berkeley, Berkeley, California, USA