[1] Mahidol Univ, Fac Med, Siriraj Hosp, Bangkok 10700, Thailand
[2] Mahidol Univ, Fac Vet Sci, Nakhon Pathom 73170, Thailand
[3] Mahidol Univ, Fac Sci, Bangkok 10400, Thailand
[4] Minist Publ Hlth, Dept Dis Control, Bur Epidemiol, Nonthaburi 11000, Thailand
[5] St Jude Childrens Res Hosp, Dept Infect Dis, Memphis, TN 38105 USA
[6] Westat Corp, Rockville, MD 20850 USA