Discovery of the H7N9 strain of avian influenza in a live poultry market in Hong Kong has resulted in the culling of 20,000 birds.

Three men in Hong Kong have died after contracting H7N9 AI in recent weeks. However, all had recently visited the Chinese mainland, local authorities said.

Infections in humans appear to be more prevalent in middle-aged or older men.

Cheung Sha Wan is the only wholesale live poultry market in Hong Kong and, following the discovery of AI, will remain closed for 21 days. All poultry at the site were culled and imports from mainland China have been temporarily halted.

The World Health Organization says there have been 206 laboratory-confirmed cases of H7N9 to date, causing more than 50 deaths. The strain displays few symptoms in poultry but can be highly pathogenic in humans.

Although the number of deaths, when compared with infections, is considered quite high, there is only one recorded incidence of the strain passing from human to human, so the risk of more widespread infection is considered low at this time.

Live bird markets where H7N9 has been detected remain closed in three cities in the Zhejiang province of mainland China.