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. 2013 May 15:5:ecurrents.outbreaks.264e737b489bef383fbcbaba60daf928.
doi: 10.1371/currents.outbreaks.264e737b489bef383fbcbaba60daf928.

Estimating Human Cases of Avian Influenza A(H7N9) from Poultry Exposure

Caitlin Rivers  1 , Kristian Lum, Bryan Lewis, Stephen Eubank
Affiliations

Estimating Human Cases of Avian Influenza A(H7N9) from Poultry Exposure

Caitlin Rivers et al. PLoS Curr. .

Abstract

In March 2013 an outbreak of avian influenza A(H7N9) was first recognized in China. To date there have been 130 cases in human, 47% of which are in men over the age of 55.The influenza strain is a novel subtype not seen before in humans; little is known about zoonotic transmission of the virus, but it is hypothesized that contact with poultry in live bird markets may be a source of exposure. The purpose of this study is to estimate the transmissibility of the virus from poultry to humans by estimating the amount of time shoppers, farmers, and live bird market retailers spend exposed to poultry each day. Results suggest that increased risk among older men is not due to greater exposure time at live bird markets.

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Figures

Human infection rate per exposure hour to poultry
Human infection rate per exposure hour to poultry
Men ages 55+ are disproportionately affected by avian influenza A(H7N9). Despite having a lower estimated exposure time to live bird markets, older men have a much higher infection rate per exposure hour than other demographic groups.
Sensitivity analysis
Sensitivity analysis
The hypothetical number of undetected cases can be estimated assuming that the infection rate per exposure hour is constant, using men ages 75+ as a reference group.
Hypothetical detection rate using men ages 75+ as the reference group
Hypothetical detection rate using men ages 75+ as the reference group
The hypothetical number of undetected cases can be estimated assuming that the infection rate per exposure hour is constant, using men ages 75+ as a reference group.
Comparison of exposure estimates reported by Cowling et al
Comparison of exposure estimates reported by Cowling et al
Cowling et al reported on the number of annual exposures to poultry in live bird markets and backyards in four regions of China. The survey was conducted in regions not reported on here, and findings were not stratified by sex. The provinces with the highest and lowest exposures were chosen to represent upper and lower bounds. Exposure values were scaled to match the time period of 30 days and applied to both male and female exposure categories. The resulting group exposure hours and infection rate per exposure hours are similar to those reported here.
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References

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