Prospective Cohort Study of Avian Influenza Transmission in Cambodia and Thailand
Session I – Benjawan, Khuntirat
Title of Contribution: Prospective Cohort Study of Avian Influenza Transmission in Cambodia and Thailand
Author(s): Benjawan Khuntirat1., Saphon Vonthanak2., Pathom Sawanpanyalert3., Whitney S. Baker4., Ana W. Capuano4., Darunee Tannitisupawong1., In-Kyu Yoon1., Thomas F. Wierzba6., Patrick J. Blair7., Matthew R. Kasper7., Sok Touch5., Krongkaew Supawat3., Malinee Chittagarnpitch3., Robert V. Gibbons1., Shannon D. Putnam7. and Gregory C. Gray4.
Affiliation(s): 1.Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand; 2.National Institute of Public Health, Ministry of Health, Phnom Penh, Kingdom of Cambodia; 3.National Institute of Health, Department of Medical Sciences and Bureau of Epidemiology, Department of Disease Control, Ministry of Public Health, Nonthaburi, Thailand; 4. Department of Epidemiology, University of Iowa College of Public Health, Iowa City, IA, USA; 5.Communicable Disease Control Department, Ministry of Health, Phnom Penh, Kingdom of Cambodia; 6.U.S. Naval Medical Research Unit No. 2, Phnom Penh, Kingdom of Cambodia; 7.U.S. Naval Medical Research Unit No. 2, Jakarta, Indonesia.
Abstract: The ongoing epizootic of highly pathogenic H5N1 among domestic poultry in Southeast Asia continues to be associated with reports of human cases. Due to endemicity within regional poultry populations, exposure and incidence of human H5N1 infections remains largely unknown. In this three year, prospective cohort study, the authors seek to describe the circumstances under which avian influenza viruses are transmitted from poultry to human adults, inducing subclinical or clinical infections and subsequent secondary transmission to case contacts. Sixteen rural Khmer and Thai villages, where H5N1 outbreaks have been previously detected, were selected for the study. From April through October 2008, field staff enrolled 1600 adults, 100 from each village, and obtained a serum sample and a baseline survey. After enrollment, influenza-like illnesses (ILI) were detected during weekly home visits or through patient reports to village-based study staff. For each ILI, medics collected a nasal swab, throat swab, and serum sample. For each laboratory-confirmed, influenza A virus infection, a household transmission study was initiated in which serum samples were collected from all consented household contacts. In addition, serum and nasal swabs were collected from consented household contacts exhibiting ILI symptoms to identify additional influenza cases. Annual serum surveys of all cohort enrollees will be conducted to estimate the annual incidence of influenza seroconversion among the cohort. Laboratory studies to identify and characterize influenza viruses include microneutralization and hemagglutination inhibition serologic techniques, RT-PCR, viral culture, and cDNA sequencing. To date, active case detection has resulted in a total of 61 ILI investigations, identifying 23 influenza A and 5 influenza B viruses. Of the 23 influenza A viruses, 3 were H1 and 20 were H3 subtypes. From a total of 60 contacts enrolled, 13 were defined as having ILI. Among these 13, 6 contacts were confirmed with influenza virus; four H3 and two H1. The authors will describe enrollment and follow-up strategies, further ILI investigation statistics, and studies of enrollment sera for evidence of previous infection with avian H5, H7, and H9 influenza viruses.
