RESUMEN
We thank Dr Viroj Wiwanitkit for his comments on our preliminary assessment of the age and sex distribution of the human cases with avian influenza A(H7N9) virus infection. To clarify, we posed three scenarios which could possibly explain the preponderance of cases among elderly men reported through China’s surveillance system: (1) differential exposure due to gender-associated practices and norms, e.g. more high-risk behaviours among elderly men; (2) differential clinical course post-exposure/infection, e.g. given similar exposures, elderly men have a more severe outcome relative to other age–gender groups; and (3) differential health care-seeking/access behaviour favouring selection of elderly men, e.g. elderly men accessing health care more than other age-gender groups.