1. Asthma and Community Health Branch, Division of Environmental Health Science and Practice, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA, USA
2. Oak Ridge Institute for Science and Education, Oak Ridge, TN, USA
3. Epidemic Intelligence Service, Center for Surveillance, Epidemiology and Laboratory Services, Centers for Disease Control and Prevention, Atlanta, GA, USA
4. Rollins School of Public Health, Emory University, Atlanta, GA, USA