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Clin Infect Dis. (2011) 53 (8): e107-e116. doi: 10.1093/cid/cir525
Evidence for Subclinical Avian Influenza Virus Infections Among Rural Thai Villagers
Benjawan P. Khuntirat1,
In-Kyu Yoon1,
Patrick J. Blair2,
Whitney S. Krueger3,4,
Malinee Chittaganpitch5,
Shannon D. Putnam2,
Krongkaew Supawat5,
Robert V. Gibbons1,
Sirima Pattamadilok5,
Pathom Sawanpanyalert5,
Gary L. Heil3,4,
John A. Friary3,4,
Ana W. Capuano6, and
Gregory C. Gray3,4
+ Author Affiliations
1Department of Virology, US Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand
2Naval Medical Research Unit #2/National Institute of Public Health, Phnom Penh, Cambodia
3Emerging Pathogens Institute and
4Department of Environmental and Global Health, College of Public Health and Health Professions, University of Florida, Gainesville, Florida
5National Institute of Health, Ministry of Public Health, Nonthaburi, Thailand
6Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, Iowa
Correspondence: Gregory C. Gray, MD, MPH, FIDSA, Professor and Chair Department of Environmental and Global Health, College of Public Health and Health Professions University of Florida, P.O. Box 100188, Gainesville, FL 32610 (gcgray@phhp.ufl.edu).
Abstract
Background. Regions of Thailand reported sporadic outbreaks of A/H5N1 highly pathogenic avian influenza (HPAI) among poultry between 2004 and 2008. Kamphaeng Phet Province, in north-central Thailand had over 50 HPAI poultry outbreaks in 2004 alone, and 1 confirmed and 2 likely other human HPAI infections between 2004 and 2006.
Methods. In 2008, we enrolled a cohort of 800 rural Thai adults living in 8 sites within Kamphaeng Phet Province in a prospective study of zoonotic influenza transmission. We studied participants’ sera with serologic assays against 16 avian, 2 swine, and 8 human influenza viruses.
Results. Among participants (mean age 49.6 years and 58% female) 65% reported lifetime poultry exposure of at least 30 consecutive minutes. Enrollees had elevated antibodies by microneutralization assay against 3 avian viruses: A/Hong Kong/1073/1999(H9N2), A/Thailand/676/2005(H5N1), and A/Thailand/384/2006(H5N1). Bivariate risk factor modeling demonstrated that male gender, lack of an indoor water source, and tobacco use were associated with elevated titers against avian H9N2 virus. Multivariate modeling suggested that increasing age, lack of an indoor water source, and chronic breathing problems were associated with infection with 1 or both HPAI H5N1 strains. Poultry exposure was not associated with positive serologic findings.
Conclusions. These data suggest that people in rural central Thailand may have experienced subclinical avian influenza infections as a result of yet unidentified environmental exposures. Lack of an indoor water source may play a role in transmission.
Evidence for Subclinical Avian Influenza Virus Infections Among Rural Thai Villagers
Benjawan P. Khuntirat1,
In-Kyu Yoon1,
Patrick J. Blair2,
Whitney S. Krueger3,4,
Malinee Chittaganpitch5,
Shannon D. Putnam2,
Krongkaew Supawat5,
Robert V. Gibbons1,
Sirima Pattamadilok5,
Pathom Sawanpanyalert5,
Gary L. Heil3,4,
John A. Friary3,4,
Ana W. Capuano6, and
Gregory C. Gray3,4
+ Author Affiliations
1Department of Virology, US Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand
2Naval Medical Research Unit #2/National Institute of Public Health, Phnom Penh, Cambodia
3Emerging Pathogens Institute and
4Department of Environmental and Global Health, College of Public Health and Health Professions, University of Florida, Gainesville, Florida
5National Institute of Health, Ministry of Public Health, Nonthaburi, Thailand
6Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, Iowa
Correspondence: Gregory C. Gray, MD, MPH, FIDSA, Professor and Chair Department of Environmental and Global Health, College of Public Health and Health Professions University of Florida, P.O. Box 100188, Gainesville, FL 32610 (gcgray@phhp.ufl.edu).
Abstract
Background. Regions of Thailand reported sporadic outbreaks of A/H5N1 highly pathogenic avian influenza (HPAI) among poultry between 2004 and 2008. Kamphaeng Phet Province, in north-central Thailand had over 50 HPAI poultry outbreaks in 2004 alone, and 1 confirmed and 2 likely other human HPAI infections between 2004 and 2006.
Methods. In 2008, we enrolled a cohort of 800 rural Thai adults living in 8 sites within Kamphaeng Phet Province in a prospective study of zoonotic influenza transmission. We studied participants’ sera with serologic assays against 16 avian, 2 swine, and 8 human influenza viruses.
Results. Among participants (mean age 49.6 years and 58% female) 65% reported lifetime poultry exposure of at least 30 consecutive minutes. Enrollees had elevated antibodies by microneutralization assay against 3 avian viruses: A/Hong Kong/1073/1999(H9N2), A/Thailand/676/2005(H5N1), and A/Thailand/384/2006(H5N1). Bivariate risk factor modeling demonstrated that male gender, lack of an indoor water source, and tobacco use were associated with elevated titers against avian H9N2 virus. Multivariate modeling suggested that increasing age, lack of an indoor water source, and chronic breathing problems were associated with infection with 1 or both HPAI H5N1 strains. Poultry exposure was not associated with positive serologic findings.
Conclusions. These data suggest that people in rural central Thailand may have experienced subclinical avian influenza infections as a result of yet unidentified environmental exposures. Lack of an indoor water source may play a role in transmission.
