H7N9 avian flu
The influenza A (H7N9) virus is one subgroup among the larger group of H7 viruses that normally circulate among birds. A number of human infections of the H7N9 virus have been reported in eastern China, mostly in the Yangtze River Delta region since late March 2013. Some of the patients have died of severe pneumonia brought on by the virus.
Bird flu strain has died down but experts say it is likely to return
The deadly H7N9 strain of bird flu that broke out on the mainland in February appears to have died down in recent weeks but could strike again in the autumn if it follows the pattern of the H5N1 virus, University of Hong Kong researchers warn.
They called for vigilance to be maintained.
There have been 131 reported cases of the virus on the mainland and in Taiwan but researchers believe this is just a fraction of the real number. Of the reported cases, 123 were admitted to hospital and 39 died.
But there have been no new cases reported since last month.
"It seems that the epidemic has ended in the past month," said Professor Gabriel Leung, director of the university's Public Health Research Centre. "In the next few months it will be important to work on preventing and preparing for its return in autumn or winter.
"Killing of chickens and market closures may still be needed when the epidemic reappears. I believe these measures should not be relaxed."
The researchers looked at cases of H5N1 - another deadly strain that broke out in 2003 - over the past decade. They found that infections never occurred from July to September.
The H7N9 strain seems to be following this pattern. Leung said analyses of humidity and natural ecology had shown that reproduction of new virus was suppressed in summer.
In China, the rate of fatalities in patients in hospital has been 36 per cent, compared with 5 to 20 per cent with H1N1 swine flu and 65 per cent in H5N1 patients.
"A one-third hospital fatality rate is not a small figure," Leung said.
After analysing data from most of the H7N9 cases and referencing it with the H1N1 outbreak in 2009, experts believe the overall death rate of H7N9 to be just 0.16 to 2.8 per cent.
So far there have been only five known mild cases of H7N9 detected by the national sentinel surveillance system, which tested patients with influenza-like illnesses in 544 hospitals across the country. All were diagnosed after they recovered.
Serum tests are being conducts on high-risk groups across the country to determine H7N9's actual prevalence.