[1] Univ Texas, Sch Publ Hlth, El Paso, TX 79902 USA
[2] Minist Publ Hlth & Social Welf, Field Epidemiol Training Program, San Salvador, El Salvador
[3] Univ Texas, Med Branch, Ctr Biodef & Emerging Infect Dis, Galveston, TX 77555 USA
[4] Univ Texas, Med Branch, Dept Pathol, Galveston, TX 77555 USA
[5] Ctr Dis Control & Prevent, Div Vector Borne Infect Dis, Ft Collins, CO 80522 USA
[6] Ctr Dis Control & Prevent, Div Int Med, Atlanta, GA 30333 USA