An influenza A (H1N1) virus that is known to circulate in U.S. swine but not humans has been detected in an adult in the state of Wisconsin, according to the U.S. Centers for Disease Control and Prevention. The patient reported occupational contact with swine prior to illness onset. No human-to-human transmission with this virus has been identified.
CDC laboratory testing has confirmed that this is a new reassortant influenza A H1N1 virus as it has acquired the matrix [M] gene from the 2009 H1N1 pandemic virus. Laboratory testing shows that the virus is susceptible to the influenza antiviral medications, oseltamivir and zanamivir.
Surveillance for additional human cases in the area has been enhanced. Providers are being asked to collect specimens for influenza virus testing from any patient presenting with influenza-like illness.
The virus identified in Wisconsin has genes from avian, swine and human influenza viruses, making it a so-called “triple reassortant” (tr) virus. Triple reassortant viruses have been circulating in U.S. swine since the 1990s. However the virus detected in Wisconsin is different from earlier triple reassortant influenza A H1N1 viruses in swine (tr-H1N1) in that it has acquired the matrix [M] gene) from the 2009 influenza A (H1N1) virus.
A review of publicly posted influenza genome sequence web sites indicates this reassortment (the tr-H1N1 virus common in swine with the 2009 H1N1 M gene) has been found in U.S. swine since 2010. However, this is the first time this genetic sequence has been detected in a human. Gene sequences of the virus detected in Wisconsin have been posted to publicly available web sites.
CDC is recommending that clinicians who suspect influenza virus infection in humans with recent exposure to swine obtain a nasopharyngeal swab from the patient for timely diagnosis at a state public health laboratory and consider empiric neuraminidase inhibitor antiviral treatment.
At this time, CDC recommends the following:
1. People who experience flu symptoms following direct or close contact with swine and who require medical attention (see below) should mention this exposure to their doctor or health care provider. (A list of flu symptoms is available at www.cdc.gov/flu/about/disease/symptoms.htm.)
2. For people who have NOT had exposure to swine and develop ILI, CDC’s recommendations for seeking treatment are the same as they are for seasonal influenza.
a. If you have symptoms of flu and are very sick or worried about your illness contact your health care provider.
b. Certain people are at greater risk of serious flu-related complications (including young children, elderly persons, pregnant women and people with certain long-term medical conditions) and this is true both for seasonal flu and variant flu virus infections. (For a full list of people at higher risk of flu-related complications, see www.cdc.gov/flu/about/disease/high_risk.htm.)
- If these people develop ILI, it’s best for them to contact their doctor. (The majority of recent variant influenza A cases have been in children.)
d. Your doctor may prescribe antiviral drugs that can treat the flu. These drugs work better for treatment the sooner they are started.