Chinese Researchers Warn H7N9 Bird Flu Could Make Big Comeback
June 24, 2013

Chinese Researchers Warn H7N9 Bird Flu Could Make Big Comeback

Lawrence LeBlond for - Your Universe Online

The H7N9 bird flu that emerged in China in March has been labeled more deadly than 2009’s H1N1 swine flu outbreak, but less severe than the H5N1 bird flu outbreak that affected the region in 2003.

Chinese researchers noted that 36 percent of hospitalizations stemming from H7N9 have resulted in death, much less than the 60 percent of deaths associated with H5N1, but slightly higher than the 21 percent of H1N1 deaths.

Reporting in The Lancet, the researchers said on Monday that H7N9 was “less serious” but more widespread than previously thought. They have warned health experts and watch dogs to not be complacent with the fact that cases have diminished since early May, saying that the virus could reemerge later this year as the warm season kicks into high gear.

Although Chinese health officials had been able to gain the upper hand in combating the outbreak, with only one person becoming infected since May 8, the researchers warned that the disease has the potential for making a stronger comeback and could spread internationally.

In total, since the first reported case in March, H7N9 has infected a total of 131 people in China and one in Taiwan, with 123 being admitted to the hospital. The National Health and Family Planning Commission (NPFPC), which had compiled data on infection rates, reported that 39 of the hospitalized cases resulted in death.

The Chinese team of researchers, led by Yu Wang of the Chinese Center for Disease Control and Prevention, concurred that H7N9 was most likely transmitted from birds, and warned that it could easily make the transition from a bird-to-human to a human-to-human transmissible strain.

With the start of the warm season on hand and a lull in H7N9 cases, Wang and his colleagues said this would be a good time for health experts to discuss a plan of action in lieu of a potential return. The team, which also includes researchers from the University of Hong Kong, said that if “H7N9 follows a similar pattern to H5N1, the epidemic could reappear in autumn.”

While there have been only 131 confirmed Chinese cases of H7N9, the researchers noted that it is possible that as many as 27,000 mild cases of the bird flu went unreported. The researchers urge that “continued vigilance and sustained intensive control efforts” are necessary.

Wang and colleagues analyzed the 123 hospital cases to ascertain the ongoing threat of the H7N9 bird flu outbreak and the overall risk of fatality pertaining to the virus. Using data from influenza-like illness (ILI) surveillance, they developed an estimate of the case-fatality risk among those with symptoms, but may or may not have needed hospital care.

As of May 28 (the date when the last case had been reported), the team found that 37 of the 123 hospitalized cases resulted in death; 69 patients had recovered from their illness; 17 patients remained hospitalized.

Based on their analysis, the team noted a fatality risk of 36 percent for all ages, with an 18 percent risk for patients younger than 60 and 49 percent for those 60 and older. In the patients who died, the team determined the median time to death was about 11 days, while median time for recovery was 18 days. Based on the ILI surveillance, the team noted the case-fatality rate among those with symptoms ranged between 0.16 percent and 2.8 percent.

Wang and colleagues cautioned that the estimates were based on several simplified assumptions, which may lead to bias if more or fewer symptomatic cases occur.

In a second paper, also reported in The Lancet, the same researchers found that men are more likely than women to be infected with H7N9 in urban areas. The team suggests this is likely due to handling infected poultry. In rural settings, most cases have been women, where it is more likely for this group to rear, slaughter and cook poultry. They also found that the average incubation period for H7N9 is 3.1 days, shorter than previous estimates.