[1] Johns Hopkins Univ, Sch Publ Hlth, Dept Environm Hlth Sci, Baltimore, MD 21205 USA
[2] Johns Hopkins Univ, Sch Publ Hlth, Dept Epidemiol, Baltimore, MD 21205 USA
[3] Johns Hopkins Univ, Sch Med, Dept Internal Med, Baltimore, MD USA
[4] Inst Salud Ambiente & Trabajo, Tlalpan, Mexico
[5] Univ Maryland, Sch Med, Dept Med, Baltimore, MD 21201 USA
[6] Holy Cross Hosp, Dept Infect Control, Silver Spring, MD USA