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H7N9 Influenza in China--What to Watch For

Image of rooster in cage
Eric Toner, MD
Date posted:
April 15, 2013
Publication type:

Our Perspective on H7N9 Influenza in China: April 15, 2013

More in this series:

April 12 • April 18 • April 24 • May 6


Center for Biosecurity staff will provide frequent updates on important news about the ongoing epidemic of H7N9 in China, along with commentary on the significance of new developments and discussion of what to look for in future news reports.

Important News

The number of confirmed cases as of 8 AM EDT, April 15, 2013, has risen to 60, with 13 deaths. This represents a 36% increase in cases in the last 48 hours; the case fatality rate has dropped slightly to 22%.1

For the first time, cases have been confirmed outside of Shanghai and its surrounding provinces in eastern China. In the past 48 hours, cases were confirmed in a child in Beijing and 2 adults in Henan Province in central China. These new cases are more than 500 miles from Shanghai.1

For the first time cases have been confirmed in close contacts. The husband of one of the very earliest cases was confirmed to have been infected as well.2

An asymptomatic carrier of the virus was reported in Beijing this morning. This asymptomatic child and another infected child in Beijing had a common source poultry contact.3


The rise in the number of confirmed cases is concerning, but it does not mean that the disease is spreading rapidly. Rather, the rise probably reflects, in large part, test kit availability country wide. When considered alongside the old cases and their location, these new cases indicate that the virus is no longer geographically confined to one area of China, which may indicate that the virus is widely spread geographically in birds and possibly in people.  

What is uncertain is how long the virus has been causing human illness in these areas. It is possible that a relatively small number of human cases of H7N9 could be hidden in the everyday larger numbers of cases of normal influenza-like-illness (ILI), pneumonia, and sepsis syndrome. Small numbers of cases may have been occurring for a while without causing unusual alarm or creating concerning patterns.  Many cases of pneumonia and sepsis syndrome lack specific microbiological diagnosis. Thus, it is possible that infections with this previously unknown virus have been occurring for some time.

We will not have a sense of the true incidence of this disease until serologic tests that provide specific evidence of prior infection with this virus can be developed and survivors of undiagnosed pneumonia can be tested. Wide scale serological surveys of people who did not have pneumonia will also be needed to determine the frequency of mild or asymptomatic infections.

However, even smaller sample size studies that convey the percentage of ILI cases in a given area where people test positive for H7N9 might be valuable for providing some sense of the extent and severity of this illness. Understanding whether the virus is in fact spreading rapidly or is just now being recognized is vitally important.

There is not yet any confirmation of human-to-human transmission, although it is likely that there are some cases of at least limited transmission among close contacts, especially family members and care givers. The confirmation of infection in both a husband and wife in Shanghai could represent person-to-person transmission but could also be explained by a common source of infection, such as exposure to poultry.

What to Watch For

Given the evidence that the virus exists across a large area, control at the source (most likely poultry markets) will be very difficult. Important factors to watch for in the days ahead include evidence of person-to-person transmission and confirmation of more asymptomatic cases.  It will be also be important to understand the extent to which diagnostic testing is being performed across China once that information is becomes available. 


  1. China confirms 60 H7N9 cases, 13 deaths. Xinhua. Updated: 2013-04-14 23:50.

  2. Schnirring L. Close-contact infection reported as China's H7N9 tally reaches 49.CIDRAP News. April 13, 2013.

  3. Beijing reports H7N9 flu virus carrier. Xinhua. April 15, 2013.



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