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. 2016 Sep;144(12):2633-40.
doi: 10.1017/S0950268816001035. Epub 2016 Jun 7.

Quantified degree of poultry exposure differs for human cases of avian influenza H5N1 and H7N9

A Bethmont  1 , C M Bui  1 , L Gardner  2 , S Sarkar  3 , A A Chughtai  1 , C R Macintyre  1
Affiliations

Quantified degree of poultry exposure differs for human cases of avian influenza H5N1 and H7N9

A Bethmont et al. Epidemiol Infect. 2016 Sep.

Abstract

Preliminary evidence suggests that direct poultry contact may play a lesser role in transmission of avian influenza A(H7N9) than A(H5N1) to humans. To better understand differences in risk factors, we quantified the degree of poultry contact reported by H5N1 and H7N9 World Health Organization-confirmed cases. We used publicly available data to classify cases by their degree of poultry contact, including direct and indirect. To account for potential data limitations, we used two methods: (1) case population method in which all cases were classified using a range of sources; and (2) case subset method in which only cases with detailed contact information from published research literature were classified. In the case population, detailed exposure information was unavailable for a large proportion of cases (H5N1, 54%; H7N9, 86%). In the case subset, direct contact proportions were higher in H5N1 cases (70·3%) than H7N9 cases (40·0%) (χ 2 = 18·5, P < 0·001), and indirect contact proportions were higher in H7N9 cases (44·6%) than H5N1 cases (19·4%) (χ 2 = 15·5, P < 0·001). Together with emerging evidence, our descriptive analysis suggests direct poultry contact is a clearer risk factor for H5N1 than for H7N9, and that other risk factors should also be considered for H7N9.

Keywords: Avian influenza; H5N1; H7N9; epidemiology; exposure.

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Figures

Fig. 1.
Fig. 1.
Algorithm for classification of WHO-confirmed cases based on reported poultry contact.
Fig. 2.
Fig. 2.
Proportion of H5N1 (n = 678) and H7N9 (n = 452) cases in each poultry contact category in the case population. (a) Unspecified contact cases categorized separately; (b) unspecified contact cases added to indirect contact; (c) unspecified contact cases added to direct contact; (d) unspecified contact cases proportionally distributed to indirect and direct contact in same proportions as original indirect and direct contact categories in case population.
Fig. 3.
Fig. 3.
Proportion of H5N1 (n = 175) and H7N9 (n = 65) cases in each poultry contact category in the case subset.
See this image and copyright information in PMC

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