title: Little evidence of subclinical avian influenza virus infections among rural villagers in Cambodia.
abstract: In 2008, 800 adults living within rural Kampong Cham Province, Cambodia were enrolled in a prospective cohort study of zoonotic influenza transmission. After enrollment, participants were contacted weekly for 24 months to identify acute influenza-like illnesses (ILI). Follow-up sera were collected at 12 and 24 months. A transmission substudy was also conducted among the family contacts of cohort members reporting ILI who were influenza A positive. Samples were assessed using serological or molecular techniques looking for evidence of infection with human and avian influenza viruses. Over 24 months, 438 ILI investigations among 284 cohort members were conducted. One cohort member was hospitalized with a H5N1 highly pathogenic avian influenza (HPAI) virus infection and withdrew from the study. Ninety-seven ILI cases (22.1%) were identified as influenza A virus infections by real-time RT-PCR; none yielded evidence for AIV. During the 2 years of follow-up, 21 participants (3.0%) had detectable antibody titers (≥ 1:10) against the studied AIVs: 1 against an avian-like A/Migratory duck/Hong Kong/MPS180/2003(H4N6), 3 against an avian-like A/Teal/Hong Kong/w312/97(H6N1), 9 (3 of which had detectible antibody titers at both 12- and 24-month follow-up) against an avian-like A/Hong Kong/1073/1999(H9N2), 6 (1 detected at both 12- and 24-month follow-up) against an avian-like A/Duck/Memphis/546/74(H11N9), and 2 against an avian-like A/Duck/Alberta/60/76(H12N5). With the exception of the one hospitalized cohort member with H5N1 infection, no other symptomatic avian influenza infections were detected among the cohort. Serological evidence for subclinical infections was sparse with only one subject showing a 4-fold rise in microneutralization titer over time against AvH12N5. In summary, despite conducting this closely monitored cohort study in a region enzootic for H5N1 HPAI, we were unable to detect subclinical avian influenza infections, suggesting either that these infections are rare or that our assays are insensitive at detecting them.
authors.affiliation: College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Gray
authors.affiliation: College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Whitney S
authors.initials: WS
authors.lastname: Krueger
authors.affiliation: Naval Medical Research Center-Asia/National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Channimol
authors.initials: C
authors.lastname: Chum
authors.affiliation: Naval Medical Research Center-Asia/National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Shannon D
authors.initials: SD
authors.lastname: Putnam
authors.affiliation: Naval Medical Research Center-Asia/National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Wierzba
authors.affiliation: College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Gary L
authors.initials: GL
authors.lastname: Heil
authors.affiliation: College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Anderson
authors.affiliation: Naval Medical Research Center-Asia/National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Chadwick Y
authors.initials: CY
authors.lastname: Yasuda
authors.affiliation: Naval Medical Research Center-Asia/National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Maya
authors.initials: M
authors.lastname: Williams
authors.affiliation: Naval Medical Research Center-Asia/National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Kasper
authors.affiliation: National Institute of Public Health/Ministry of Health, Phnom Penh, Cambodia.
authors.forename: Vonthanak
authors.initials: V
authors.lastname: Saphonn
authors.affiliation: Naval Medical Research Center-Asia/National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Blair
mesh_terms: D000328:Adult; D002160:Cambodia / Q000453:epidemiology; D015331:Cohort Studies; D006801:Humans; D053124:Influenza A Virus, H5N1 Subtype / Q000502:physiology; D053127:Influenza A Virus, H9N2 Subtype / Q000502:physiology; D007251:Influenza, Human / Q000453:epidemiology*; D012424:Rural Population / Q000706:statistics & numerical data*