1. Centre for Endemic Disease Control, Chinese Centre for Disease Control and Prevention, Harbin Medical University, Key Lab of Etiology and Epidemiology, Education Bureau of Heilongjiang Province & National Health and Family Planning Commission (23618504), Harbin, China
2. Water Sanitation and Personal Hygiene Projects Office, United Nations International Children's Emergency Fund (UNICEF) Beijing Office, Beijing, China
3. Biometrics Division, Smerud Medical Research, Oslo, Norway