WHO Update on Human Infection with Influenza A (H7N9) Virus in China

As of April 14, 2013, the National Health and Family Planning Commission notified the World Health Organization (WHO) of an additional two laboratory-confirmed cases of human infection with influenza A(H7N9) virus from Henan in China. The first patient is a 34-year-old man who became ill on April 6, 2013, and the second patient is a 65-year-old man who became ill on April 8, 2013. To date, a total of 51 patients have been laboratory-confirmed with influenza A(H7N9) virus in China; including 11 deaths. More than 1,000 close contacts of the confirmed cases are being closely monitored.
 
Investigations into the possible sources of infection and reservoirs of the virus are ongoing. Until the source of infection has been identified, it is expected that there will be further cases of human infection with the virus in China. So far, there is no evidence of ongoing human-to-human transmission.
 
The WHO does not advise special screening at points of entry with regard to this event, nor does it recommend that any travel or trade restrictions be applied.
 
To date, there is limited information to determine whether the reported number of cases represents some or all of the cases actually occurring. As some relatively mild cases of illness have now been reported, it is possible that there are other such cases that have not been identified and reported.

On April 1, 2013, the WHO first reported three human infections with a new influenza A (H7N9) virus in China. Since then, additional cases have been reported. Most reported cases have severe respiratory illness and, in some cases, have died. At this time, no cases of H7N9 outside of China have been reported. The new H7N9 virus has not been detected in people or birds in the United States.

This new H7N9 virus is an avian (bird) influenza (flu) virus. Human infections with avian influenza (AI, or bird flu) are rare but have occurred in the past, most commonly after exposure to infected poultry. However, this is the first time that this bird flu subtype (H7N9) has been found in people. This virus is very different from other H7N9 viruses previously found in birds.

An investigation by Chinese authorities is ongoing. H7N9 viruses have been detected in poultry in the same area where human infections have occurred. Many of the human cases of H7N9 are reported to have had contact with poultry. However some cases reportedly have not had such contact. Close contacts of confirmed H7N9 patients are being followed to see if any human-to-human spread of H7N9 might have occurred. Based on previous experience with other avian influenza viruses most notably H5N1 some limited human-to-human spread of this H7N9 virus would not be surprising. Most importantly, however, no sustained person-to-person spread of the H7N9 virus has been found at this time. Ongoing (sustained) person-to-person spread is necessary for a pandemic to occur.

This is a novel (non-human) virus and therefore has the potential to cause a pandemic if it were to change to become easily and sustainably spread from person-to-person. So far, this virus has not been determined to have that capability. However, influenza viruses constantly change and its possible that this virus could gain that ability. The Centers for Disease Control and Prevention (CDC) takes routine preparedness actions whenever a new virus with pandemic potential is identified, including developing a candidate vaccine virus to make a vaccine if it were to be needed. There is no licensed H7 vaccine available at this time.

The CDC is following this situation closely and coordinating with domestic and international partners. In addition, the CDC has issued guidance to U.S. clinicians and public health departments on how to test for this virus, and interim guidance on case definitions for possible H7N9 cases in the United States and interim infection control guidance for U.S. healthcare workers. The CDC also has developed information for travelers to China.