APEIR Publication

Answer

WHO in April 1st 2013, an outbreak of human infections with a new avian influenza A (H7N9) virus was first reported in China.  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).

What is H7N9?

Avian influenza A H7 viruses are a group of influenza viruses that normally circulate among birds. The avian influenza A(H7N9) virus is one subgroup among the larger group of H7 viruses. Although some H7 viruses (H7N2, H7N3 and H7N7) have occasionally been found to infect humans, no human infections with H7N9 viruses have been reported until recent reports from China..  Beginning at the end of March 2013, China reported human and bird (poultry) infections with a new strain of H7N9 that is very different from previously seen H7N9 viruses.

Is this new strain of H7N9 infecting humans?

Yes. While H7N9 viruses had never before been detected in people, from March 31 through April 30, 2013, China reported more than 126 cases of human infection with this new H7N9 virus.

How are people becoming infected with the avian influenza A(H7N9) virus?

At this point it is not known how persons are becoming infected. Some of the confirmed cases had contact with animals or with environments where animals are housed. The virus has now been found in chickens, ducks, and captive-bred pigeons at live bird markets near locations where cases have been reported. The possibility of an animal source of the infection is being investigated, as is the possibility of person-to-person transmission.

Is it possible that this virus will spread from person-to-person?

Yes. Based on what we know about human infections with other bird flu viruses, it’s possible and even likely that there will be some limited person-to-person spread with th