The WHO says the woman, who died in March, probably contracted the virus at a live poultry market and the risk of further spread is low.

While H3N8 is “one of the most frequently found” subtypes of flu in birds, it had not been detected in humans before two cases emerged in April and May last year, both in China.

In a statement, the WHO said the woman, who had pre-existing medical conditions including cancer, had been admitted to hospital with severe pneumonia after falling ill in February. She died last month.

“The case was detected through the severe acute respiratory infection (SARI) surveillance system. No close contacts of the case developed an infection or symptoms of illness at the time of reporting,” WHO said in its statement on Monday.

All three people who contracted H3N8 in China are thought to have been exposed to the virus at live poultry markets. The United Nations health agency said the Chinese government had stepped up monitoring for the strain and that the risk of more infections was low.

“However, due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect virologic, epidemiologic and clinical changes associated with circulating influenza viruses which may affect human (or animal) health,” it said.

The H3N8 infection is unrelated to the H5N1 bird flu pandemic, which has devastated poultry and wild birds around the world in the last 18 months and has spread to mammals including foxes, bears and domestic cats.

To infect humans, the H5N1 virus has to attach itself to receptors in the lungs, which the virus lacks the ability to readily bond with, William Schaffner, a professor of medicine at Vanderbilt University’s Division of Infectious Diseases, told Al Jazeera in February.

Forced adaptation to replicating in the lungs is why only poultry workers, who breathe in contaminated faecal dust, are typically infected, Schaffner added.

The H3N8 virus is less dangerous for both wild birds and domestic poultry than H5N1, and is known to have been circulating since 2002 after first emerging in North American waterfowl.

It is also known to infect horses, dogs and seals.