title: Estimating Risks of Inapparent Avian Exposure for Human Infection: Avian Influenza Virus A (H7N9) in Zhejiang Province, China.
abstract: Inapparent avian exposure was suspected for the sporadic infection of avian influenza A(H7N9) occurring in China. This type of exposure is usually unnoticed and difficult to model and measure. Infected poultry with avian influenza H7N9 virus typically remains asymptomatic, which may facilitate infection through inapparent poultry/bird exposure, especially in a country with widespread practice of backyard poultry. The present study proposed a novel approach that integrated ecological and case-control methods to quantify the risk of inapparent avian exposure on human H7N9 infection. Significant associations of the infection with chicken and goose densities, but not with duck density, were identified after adjusting for spatial clustering effects of the H7N9 cases across multiple geographic scales of neighborhood, community, district and city levels. These exposure risks varied geographically in association with proximity to rivers and lakes that were also proxies for inapparent exposure to avian-related environment. Males, elderly people, and farmers were high-risk subgroups for the virus infection. These findings enable health officials to target educational programs and awareness training in specific locations to reduce the risks of inapparent exposure.
authors.affiliation: Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
authors.forename: Erjia
authors.initials: E
authors.lastname: Ge
authors.affiliation: Zhejiang Provincial Center for Disease Prevention &Control, Hangzhou, P.R. China.
authors.forename: Renjie
authors.initials: R
authors.lastname: Zhang
authors.affiliation: School of Mathematics &Statistics, Xi'an Jiaotong University, Xi'an, P.R. China.
authors.forename: Dengkui
authors.initials: D
authors.lastname: Li
authors.affiliation: Division of Clinical Public Health and Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Wei
authors.affiliation: Zhejiang Provincial Center for Disease Prevention &Control, Hangzhou, P.R. China.
authors.forename: Xiaomeng
authors.initials: X
authors.lastname: Wang
authors.forename: Poh-Chin
authors.initials: PC
authors.lastname: Lai
mesh_terms: D000367:Age Factors; D000818:Animals; D002645:Chickens; D002681:China / Q000453:epidemiology; D004372:Ducks; D004781:Environmental Exposure; D005777:Geese; D005843:Geography; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype / Q000302:isolation & purification*; D005585:Influenza in Birds / Q000635:transmission*; D007251:Influenza, Human / Q000453:epidemiology*; D018570:Risk Assessment; D012737:Sex Factors