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Novel H7N9 Influenza Virus Infecting People in China

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May 24, 2013

A new strain of avian influenza A H7N9 ("bird flu") has infected 131 people and caused 36 deaths (as of May 17) in China since the first cases were reported in March, according to the World Health Organization (WHO). The virus is raising concern because it does not typically infect humans, but the Centers for Disease Control and Prevention (CDC) reports that evidence suggests the majority of those affected came into contact with infected poultry or contaminated environments.

Most of the confirmed H7N9 cases have occurred in the provinces around Shanghai, with a reported 106 infections and 23 deaths. These numbers are based on reports from provincial public health authorities and may be greater than the national reports, which are now being released once per week.

While no cases have been found in the U.S. or in travelers returning to the U.S., the CDC is providing information about the virus to healthcare practitioners and public health professionals in an effort to protect against spread of the infection. Scientists and governmental health authorities are keeping a close watch on how the virus is transmitted to guard against person-to-person spread, which could trigger a pandemic.

The new strain is genetically different from other avian influenza A viruses, much like the genetic differences observed in the highly pathogenic H5N1 bird flu virus that has been monitored since November 2003 and has caused death in 60% of those infected. Symptoms of H7N9 are more severe than other H7 viruses previously seen, and officials note that it has the potential to adapt or genetically blend (reassort) with other human influenza viruses and begin spreading from person to person. However, the Chinese National Health and Family Planning Commission is following up on reported cases and as of yet has not found transmission of the virus among people.

Infected birds often do not show symptoms of H7N9 but still release a large amount of the virus in their droppings and mucus. Chinese health authorities are still assessing the extent of the outbreak among birds, and people may come into contact with infected birds but not be aware of their exposure until they start showing symptoms. Many H7N9 patients have experienced high fever and coughing at the onset of infection, often progressing to severe respiratory illnesses including pneumonia and acute respiratory distress syndrome (ARDS), advancing to failure of several organs (lungs, kidneys), and causing death. Older men with underlying medical conditions make up the majority of reported cases.

The CDC has not announced any travel restrictions to China but is closely monitoring the situation, advising that travelers pay attention to their hygiene and food safety practices. The agency recommends avoiding all contact with birds, pigs and other animals, eating only food that is fully cooked, and washing hands often. Visit the U.S. Department of State web site to find a doctor if you become ill in China. If you experience coughing, fever or shortness of breath after returning from China, the CDC recommends visiting your doctor immediately and explaining your recent visit.

As part of their response to the outbreak, the CDC developed a new diagnostic test kit to identify the H7N9 virus and began distributing the kits to Department of Defense and public health laboratories both in the U.S. and internationally in May. The kits are meant to provide assistance for diagnosing and controlling spread of the disease. Travelers returning from China to the U.S. who develop a respiratory illness are being tested for H7N9 infection and, to date, all test results have been negative.

The CDC and its partnering labs are also working on developing a vaccine should one become necessary. Producing a vaccine could take several months. Studies have also found that the antiviral drugs oseltamivir (Tamiflu) and zanamivir (Relenza) would be effective treatments for H7N9 infection and have the greatest benefit when administered within the first 3 days of the appearance of symptoms.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used. To access online sources, copy and paste the URL into your browser.

World Health Organization. Human Infection with Avian Influenza A (H7N9) Virus – Update. Global Alert and Response (GAR). May 17, 2013. Available online at through Accessed May 22, 2013.

Centers for Disease Control and Prevention. H7N9: Frequently Asked Questions. May 1, 2013. Available online at through Accessed May 10, 2013.

Centers for Disease Control and Prevention. Emergence of Avian Influenza A (H7N9) Virus Causing Severe Human Illness – China, February-April, 2013. MMWR. May 1, 2013. Available online at through Accessed May 10, 2013.

World Health Organization. Number of Confirmed Human Cases for Avian Influenza A (H7N9) Reported to WHO. Report 4. May 1, 2013. PDF available for download at through Accessed May 10, 2013.

Centers for Disease Control and Prevention. Watch: Level 1, Practice Usual Precautions Avian Flu (H7N9). Travelers' Health. May 8, 2013. Available online at through Accessed May 10, 2013.

Centers for Disease Control and Prevention. H7N9 Update; CDC Pandemic Preparedness Activities Progress. April 26, 2013. Available online at through Accessed May 2013. Accessed May 10, 2013.