[1] Chiang Mai Univ, Fac Med, Dept Community Med, Chiang Mai 50200, Thailand
[2] Chiang Mai Univ, Fac Med, Dept Community Med, Occupat & Environm Med Unit, Chiang Mai 50200, Thailand
[3] Mahidol Univ, Hosp Trop Dis, Fac Trop Med, Thai Travel Clin, Bangkok 10400, Thailand
[4] Mahidol Univ, Fac Trop Med, Dept Clin Trop Med, Travel Med Res Unit, Bangkok 10400, Thailand