Risk Factors for Human Illness with Avian Influenza A (H5N1) Virus Infection in China

(See the article by Tiensin et al. on pages 1735 – 43, the article by Vong et al. on pages 1744 –52, and the editorial commentary by Briand and Fukuda on pages 1717–9) Background. In China, 30 human cases of avian influenza A (H5N1) virus infection were identified through July 2008. We conducted a retrospective case-control study to identify risk factors for influenza H5N1 disease in China. Methods. A questionnaire about potential influenza H5N1 exposures was administered to 28 patients with in-fluenza H5N1 and to 134 randomly selected control subjects matched by age, sex, and location or to proxies. Condi-tional logistic regression analyses were performed. Results. Before their illness, patients living in urban areas had visited wet poultry markets, and patients living in rural areas had exposure to sick or dead backyard poultry. In multivariable analyses, independent risk factors for influenza H5N1 were direct contact with sick or dead poultry (odds ratio [OR], 506.6 [95 % confidence interval {CI}, 15.7–16319.6]; P .001), indirect exposure to sick or dead poultry (OR, 56.9 [95 % CI, 4.3–745.6]; P .002), and visiting a wet poultry market (OR, 15.4 [95 % CI, 3.0–80.2]; P .001). Conclusions. To prevent human influenza H5N1 in China, the level of education about avoiding direct or clos