This past week, 23 people in China have been infected with the H7N9 strain of bird flu, the World Health Organization (WHO) said on Monday, in addition to the previous week that saw 24 new cases which confirms this virus is becoming more active.

In the newest cases, reported from several different provinces of China, was a 38-year-old man who died on Jan. 9.

The others were in hospitals, some in serious or critical condition, the WHO said. Several had reported recent exposure to poultry or poultry markets, but the WHO said the source of the virus was still under investigation.

The H7N9 bird flu virus emerged in March last year and has so far infected at least 199 people in China, Taiwan and Hong Kong, killing 52 of them, according to an update from the WHO’s spokesman Gregory Hartl.

Some cases were said to be due to close contact to another infected person, but WHO said on Monday that “so far, there is no evidence of sustained human-to-human transmission.”

Hartl told Reuters last week that the United Nations health agency had noted the recent rapid increase in human H7N9 infections and was keeping a watchful eye.

“So far we haven’t seen anything that causes us to change our risk assessment,” he said.

The WHO’s assessment is that “the current likelihood of community-level spread … is considered to be low.”

But, scientists warn that the H7N9 virus contains genetic markers that could help it infect mammals easier than other avian viruses. Infected birds also do not show symptoms, making it harder to track the disease.

“After almost a decade of sitting on the proverbial edge of the H5N1 pandemic cliff and not falling off, people are beginning to think that we never will fall,” Michael Osterholm, an infectious disease expert at the University of Minnesota, said by email. “But the best scientific assessment of microbial genetics tells us we could still fall off of that cliff and if we do, the global consequences could be devastating.”

Experts are blaming the current infection on the winter flu season for the significant increase in the number of cases of human H7N9 infection. However, the CDC and the WHO are obviously concerned.

Public health authorities and doctors have been put on alert to watch for signs that the more active circulating virus might be mutating and adapting, allowing transmission between people.

Image via NDN