[1] Univ Minnesota, Sch Publ Hlth, Div Epidemiol, Minneapolis, MN 55455 USA
[2] Univ Minnesota, Sch Publ Hlth, Div Infect Dis, Minneapolis, MN USA
[3] Univ Minnesota, Sch Med, Minneapolis, MN 55455 USA
[4] Bach Mai Hosp, Dept Neurol, Hanoi, Vietnam
[5] Univ Wisconsin, Sch Med, Dept Prevent Med, Madison, WI 53706 USA
[6] Ctr Dis Control & Prevent, Div Vector Borne Infect Dis, Ft Collins, CO 80522 USA