Department of Microbiology,Faculty of Public Health,Mahidol University,Bangkok 10400,Thailand;
Center for Nosocomial Infection Control,Nopparatjathanee Hospital,Bangkok,Thailand;
Department ofEnvironmental Health,Faculty of Public Health,Mahidol University,Bangkok 10400,Thailand;
Center for Nosocomial Infection Control,Nopparatjathanee Hospital,Bangkok,Thailand;