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.
Highlights
Inapparent avian exposure was suspected for the sporadic infection of avian influenza A(H7N9) occurring in China
The present study proposed a novel approach that integrated ecological and casecontrol methods to quantify the risk of inapparent avian exposure on human H7N9 infection
Significant associations between disease clusters and human H7N9 infection were noted across all four spatial scales but neighborhood-level disease clusters markedly increased the odds of human infection. This is a novel study that integrates epidemiology and health geography to quantify the effects of inapparent exposure to poultry and proximity to inland waters on human H7N9 infection through a set of individual-level cases (H7N9) and their matched controls (TB)
Summary
Inapparent avian exposure was suspected for the sporadic infection of avian influenza A(H7N9) occurring in China. 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 proxies for inapparent exposure to avian-related environment. Poultry and LPM densities have been used as proxies for estimating the risks of outdoor environmental exposure to poultry[23] In these studies, areal units (such as 1 × 1 km[2] pixel) without H7N9 cases were randomly selected to generate pseudo-absence data on infection. The study made an attempt to answer the following questions: 1) Are poultry densities, species, and distances/proximity to inland waters (i.e., rivers and lakes) associated with human H7N9 infection and what are the relative contributions of each variable to the occurrence of human H7N9 infection? 2) Do these variables vary geographically and exert interactive impacts to increase the risks of infection? and 3) Who are the target high-risk populations: male vs. female, adult vs. elderly, or farmer vs. worker vs. other occupation subgroups?
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