Influenza A (H7N9) emerged in China as a zoonotic virus in March 2013.

As of 1 March 2016, a total of 736 human cases had been reported, of which 283 had a fatal outcome (38% case fatality rate). Most cases reported a history of direct or indirect exposure to live domestic poultry at live bird markets (LBMs).

Through active surveillance, the H7N9 virus was detected in live birds and the environment of LBMs and, to a lesser extent, on farms. Infected birds shed virus without showing any clinical signs.

This “silent” infection increases the likelihood of undetected virus spread, and consequently of human exposure. As a result, passive, event-based surveillance cannot be applied for the early detection of H7N9 in poultry populations. Instead, surveillance needs to follow a risk-based approach for early detection, with active sampling and virological testing, targeting those geographic areas, markets, and production systems at highest risk of virus introduction.