H7N9

The novel H7N9 avian flu appears to be less severe than the highly pathogenic H5N1 avian flu but more severe than the 2009 pandemic H1N1 flu, researchers reported.

The first estimate of the severity profile of the novel flu suggests that it kills 36% of those who are admitted to a hospital, according to Chinese researchers led by Yu Wang, PhD, of the Chinese equivalent of the CDC in Beijing.

That's lower than the 60% observed worldwide with H5N1, but higher than the 21% seen in China with the pandemic H1N1 strain, the researchers reported online in The Lancet.

n a separate paper in the journal, the same group of researchers found epidemiological similarities and differences between the two avian influenza strains and warned that -- if they follow similar temporal patterns -- the H7N9 flu could recur this fall.

The severity estimates are the best that can be done "in view of the available information," commented Cécile Viboud, PhD, of the NIH in Bethesda, Md., and Lone Simonsen, PhD, of George Washington University in Washington, D.C.

But the uncertainty surrounding them means "public health experts will have to make policy decisions on the basis of uncomfortably broad confidence limits" when and if the flu returns, they argued in an accompanying commentary.

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 other hand, they noted, it is "reassuring" that the data suggest a substantially less severe disease course for the H7N9 flu than has been seen for H5N1.

According to the World Health Organization, there have been 630 laboratory-confirmed human cases of H5N1 infection since 2003, of which 375 resulted in death.

he agency is also reporting 132 laboratory-confirmed cases of H7N9 flu, including 37 deaths.

For their analysis, Wang and colleagues estimated the risk of fatality, mechanical ventilation, and admission to intensive care for the 123 patients who required hospital admission for medical reasons.

They used data from sentinel influenza-like illness (ILI) surveillance to develop an estimate of the case-fatality risk among patients who had symptoms, but who may or may not have needed hospital care.

•  (on admission for all ages)
• Mechanical ventilation or death: 69% (the comparator was recovery without needing ventilation)
• Admission to intensive care, mechanical ventilation, or fatality: 83% (where the comparator was recovery without needing intensive care or ventilation)

Interestingly, they reported, the fatality risk estimate varied significantly by age (at P=0.0019) -- 18% for those younger than 60 and 49% for those 60 and older.

• Fatality: 36% 

  For the people who died, the median time to death was -- 11 days, while for those who recovered the median time to recovery was 18 days.

  Depending on assumptions about the coverage of the sentinel surveillance network and how patients with ILI sought healthcare, the case-fatality rate among patients with symptoms ranged between 0.16% and 2.8%, Wang and colleagues reported.

  ess, the results "support continued vigilance and sustained intensive control efforts against the virus to minimize risk of human infection, which is greater than previously recognized," they argued.

  In the second paper, the researchers found that in urban areas -- for both H7N9 and H5N2 flu -- men were more likely to be infected, suggesting that one of the main risk factors is handling infected poultry.

  In the countryside, where most Chinese cases of H5N1 since 2003 have occurred, most victims have been women, possibly because they would have had greater exposure to "rearing, slaughtering, and cooking of backyard poultry" than men.

  In the cities, however, men would be involved in obtaining poultry from live markets and would thus be more likely to be exposed, the researchers suggested.

  The average incubation periods of the two viruses are similar, they reported -- 3.1 days for H7N9 (shorter than previous estimates) and 3.3 days for H5N1.

  They also found that the median age of people with confirmed H7N9 infection was 62, compared with 26 for H5N1.

  In urban areas, 74% of patients with both viruses were men, but in rural areas the proportions of the viruses in men were 62% for H7N9 and 33% for H5N1.

  And 75% of patients with H7N9 and 71% of those with H5N1 reported recent exposure to poultry.

  The researchers also noted that the onset of warmer weather appears to 

  have led to a retreat by the H7N9 flu, with only one new confirmed case since May 8.

  But "if H7N9 follows a similar pattern to H5N1, the epidemic could reappear in the autumn," they warned.

  They added that the lull provides an opportunity to fine-tune preventive public health measures and clinical management, as well as to build up regional capacity to cope with the possibility that H7N9 could spread beyond China.