Avian Influenza A (H7N9) Virus
An outbreak of human infections with a new avian influenza A (H7N9) virus was first reported in China by the World Health Organization on April 1, 2013. The virus was detected in poultry in China as well. Most human infections are believed to have occurred after exposure to infected poultry or contaminated environments.
During the spring of 2013, 135 H7N9 human infections were reported, the vast majority with illness onset during the month of April; 44 people died. Only 5 cases were detected over the summer. To date this fall, four human cases have been reported; all with illness onset in October. Most of the recent cases also had poultry exposure and lived in areas where H7N9 had been found previously. The decrease in H7N9 cases over the summer likely resulted from a combination of control measures taken by Chinese authorities - like closing live bird markets - and a change in weather. Studies indicate that avian influenza viruses, like seasonal influenza viruses, have a seasonal pattern: they circulate at higher levels in cold weather and at lower levels in warm weather. The October cases coincide with the arrival of cooler weather in China and are not unexpected. In fact, it’s likely that cases of H7N9 will continue to be detected in China and possibly in neighboring countries during the fall and winter.
While some mild illnesses in human H7N9 cases have been seen, most patients have had severe respiratory illness, about one-third leading to death. Close contacts of confirmed H7N9 patients have been followed to determine whether any human-to-human spread of H7N9 has occurred. No evidence of sustained person-to-person spread of H7N9 has been found, though some evidence points to limited person-to-person spread in rare circumstances. Limited person to person spread of bird flu is thought to have occurred rarely in the past, most notably with avian influenza A (H5N1), and so would not be surprising with H7N9. No cases of H7N9 outside of China have been reported, and the new H7N9 virus has not been detected in people or birds in the United States.
Most concerning about this situation is the pandemic potential of this virus. Influenza viruses constantly change and it’s possible that this virus could gain the ability to spread easily and sustainably among people, triggering a global outbreak of disease (pandemic). CDC is following this situation closely and coordinating with domestic and international partners. 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. Those preparedness measures have continued over the summer. CDC also has issued guidance to clinicians and public health authorities in the United States, as well as provided information for people traveling to China. CDC will provide updated information as it becomes available.
H7N9 Features, Background on Human Infections…
Frequently Asked Questions…
H7N9 Outbreak Characterization
- H7N9 infections in people and poultry in China
- Sporadic infections in humans; many with poultry exposure
- No sustained or community transmission
What's New & Updated
H7N9: What should I do?
- CDC does not have any new or special recommendations for the U.S. public at this time regarding H7N9. CDC will keep you updated. Stay informed.
- Since H7N9 is not spreading easily from person to person at this time, CDC does not recommend that people delay or cancel trips to China. The World Health Organization also is watching this situation closely and does not recommend any travel restrictions.
- CDC advises travelers to China to take some common sense precautions, like not touching birds or other animals and washing hands often. Poultry and poultry products should be fully cooked. CDC will update its advice for travelers if the situation in China changes. This guidance is available at Avian Flu (H7N9) in China.