Frequently Asked Questions on human infection with influenza A(H7N9) virus, China
Update as of 3 April 2013
Note that this document supersedes the previous version. Updates will be posted as new information becomes available.
1. What is the influenza A(H7N9) virus?
Influenza A H7 viruses are a group of influenza viruses that normally circulate among birds. The 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.
2. What are the main symptoms of human infection with influenza A(H7N9) virus?
Thus far, patients with this infection have had severe pneumonia. Symptoms include fever, cough and shortness of breath. However, information is still limited about the full spectrum of disease that infection with influenza A(H7N9) virus might cause.
3. How many human cases of influenza A(H7N9) virus have been reported in China to date?
As of 3 April 2013, seven laboratory-confirmed cases have been detected in China. Details of the most current information on cases can be found in Disease Outbreak News.
4. Why is this virus infecting humans now?
We do not know the answer to this question yet, because we do not know the source of exposure for these human infections. However, analysis of the genes of these viruses suggests that although they have evolved from avian (bird) viruses, they show signs of adaption to growth in mammalian species. These adaptations include an ability to bind to mammalian cells, and to grow at temperatures close to the normal body temperature of mammals (which is lower than that of birds).
5. What is known about previous human infections with H7 influenza viruses globally?
From 1996 to 2012, human infections with H7 influenza viruses (H7N2, H7N3, and H7N7) were reported in Netherlands, Italy, Canada, USA, Mexico and the United Kingdom. Most of these infections occurred in association with poultry outbreaks. The infections mainly resulted in conjunctivitis and mild upper respiratory symptoms, with the exception of one death, which occurred in the Netherlands. Until now, no human infections with H7 influenza viruses have been reported in China.
6. Is the influenza A(H7N9) virus different from influenza A(H1N1) and A(H5N1) viruses?
Yes. All three viruses are influenza A viruses but they are distinct from each other. H7N9 and H5N1 are considered animal influenza viruses that sometimes infect people. H1N1 viruses can be divided into those that normally infect people and those that normally infect animals.
7. How did people become infected with the influenza A(H7N9) virus?
Some of the confirmed cases had contact with animals or with an animal environment but the virus has not thus far been found in animals. It is not yet known how these persons became infected. The possibility of animal-to-human transmission is being investigated, as is the possibility of person-to-person transmission.
8. How can infection with influenza A(H7N9) virus be prevented?
Although both the source of infection and the mode of transmission are uncertain, it is prudent to follow basic hygienic practices to prevent infection. They include hand and respiratory hygiene and food safety measures.
• Wash your hands before, during, and after you prepare food; before you eat; after you use the toilet; after handling animals or animal waste; when your hands are dirty; and when providing care when someone in your home is sick. Hand hygiene will also prevent the transmission of infections to yourself (from touching contaminated surfaces) and in hospitals to patients, health care workers and others.
• Wash your hands with soap and running water when visibly dirty; if not visibly dirty, wash your hands with soap and water or use an alcohol-based hand cleanser.
• Cover your mouth and nose with a medical mask, tissue, or a sleeve or flexed elbow when coughing or sneezing; throw the used tissue into a closed bin immediately after use; perform hand hygiene after contact with respiratory secretions.
9. Is it safe to eat meat, i.e. poultry and pork products?
Although we do not yet know the mode of transmission, it is prudent to follow basic principles of hygienic food preparation, as follows: Diseased animals should not be eaten. Otherwise, it is safe to eat properly prepared and cooked meat. Because influenza viruses are inactivated by sufficient heating, normal temperatures used for cooking (such that food reaches 70°C in all parts— "piping" hot — no "pink" parts) will kill the virus. In areas experiencing outbreaks, meat products can be safely consumed provided that these items are properly cooked and properly handled during food preparation. The consumption of raw meat and uncooked blood-based dishes is a high-risk practice and is discouraged. Always keep raw meat separate from cooked or ready-to-eat foods to avoid contamination. Do not use the same chopping board or the same knife for raw meat and other foods. Do not handle both raw and cooked foods without washing your hands in between and do not place cooked meat back on the same plate or surface it was on before cooking. Do not use raw or soft-boiled eggs in food preparations that will not be heat treated or cooked. After handling raw meat, wash your hands thoroughly with soap and water. Wash and disinfect all surfaces and utensils that have been in contact with raw meat.
10. Is there a vaccine for the influenza A(H7N9) virus?
No vaccine for the prevention of influenza A(H7N9) infections is currently available. However, viruses have already been isolated and characterized from the initial cases. The first step in development of a vaccine is the selection of candidate viruses that could go into a vaccine. WHO, in collaboration with partners, will continue to characterize available influenza A(H7N9) viruses to identify the best candidate viruses. These candidate vaccine viruses can then be used for the manufacture of vaccine if this step becomes necessary.
11. Does treatment exist for influenza A(H7N9) infection?
Laboratory testing conducted in China has shown that the influenza A(H7N9) viruses are sensitive to the anti-influenza drugs known as neuraminidase inhibitors (oseltamivir and zanamivir). When these drugs are given early in the course of illness, they have been found to be effective against seasonal influenza virus and influenza A(H5N1) virus infection. However, at this time, there is no experience with the use of these drugs for the treatment of H7N9 infection.
12. Is the general population at risk from the influenza A(H7N9) virus?
We do not yet know enough about these infections to determine whether there is a significant risk of community spread. This possibility is the subject of epidemiological investigations that are now taking place.
13. Are health care workers at risk from the influenza A(H7N9) influenza virus?
Health care workers often come into contact with patients with infectious diseases. Therefore, WHO recommends that appropriate infection prevention and control measures be consistently applied in health care settings, and that the health status of health care workers be closely monitored. Together with standard precautions, health care workers caring for those suspected or confirmed to have influenza A(H7N9) infection should use additional precautions (http://www.who.int/csr/resources/publications/swineflu/WHO_CDS_EPR_2007_6/en/index.html).
14. What investigations have begun?
Local and national health authorities are taking the following measures, among others:
• Enhanced surveillance for pneumonia cases of unknown origin to ensure early detection and laboratory confirmation of new cases;
• Epidemiological investigation, including assessment of suspected cases and contacts of known cases;
• Close collaboration with animal health authorities to determine the source of the infection.
15. Does this influenza virus pose a pandemic threat?
Any animal influenza virus that develops the ability to infect people is a theoretical risk to cause a pandemic. However, whether the influenza A(H7N9) virus could actually cause a pandemic is unknown. Other animal influenza viruses that have been found to occasionally infect people have not gone on to cause a pandemic.
16. Is it safe to travel to China?
The number of cases identified in China is very low. WHO does not advise the application of any travel measures with respect to visitors to China nor to persons leaving China.
17. Are Chinese products safe?
There is no evidence to link the current cases with any Chinese products. WHO advises against any restrictions to trade at this time.