Seasonal Influenza (Flu)

Add this to...
Añadir en...
Favorites
Delicious
Digg
Google Bookmarks

Situation Summary on Influenza A (H3N2) Variant Viruses (“H3N2v”)

Situation Update

Since July 2012, there have been outbreaks of H3N2 variant viruses with the matrix (M) gene from the 2009 H1N1 pandemic virus in multiple U.S. states. Investigations into H3N2v cases indicate that the main risk factor for infection is prolonged exposure to pigs, mostly in fair settings. Found in U.S. pigs in 2010 and humans in July 2011, this virus appears to spread more easily from pigs to people than other variant viruses. Though limited person-to-person spread with this virus has occurred, no sustained community spread of H3N2v has been detected at this time. Associated illness so far has been mostly mild with symptoms similar to seasonal flu and most cases have occurred in children who have little immunity against this virus. Like seasonal flu, however, serious illness, resulting in hospitalization and death is possible. People at high risk of serious complications from H3N2v include children younger than 5, people with certain chronic conditions like asthma, diabetes, heart disease, weakened immune systems, pregnant women and people 65 years and older. These people are urged to avoid pigs and pig arenas at fairs this season. The Centers for Disease Control and Prevention (CDC) is working with states to respond to these outbreaks and continues to monitor the situation closely.

See Past Updates »

Background

Swine flu viruses do not normally infect humans. However, sporadic human infections with influenza viruses that normally circulate in swine and not people have occurred. When this happens, these viruses are called “variant viruses.” They also can be denoted by adding the letter “v” to the end of the virus subtype designation. Human infections with H1N1v, H3N2v and H1N2v viruses have been detected in the United States. Most commonly, human infections with variant viruses occur in people with exposure to infected pigs (e.g. children near pigs at a fair or workers in the swine industry). This is thought to happen mainly when an infected pig coughs or sneezes and droplets with influenza virus in them spread through the air. If these droplets land in your nose or mouth, or are inhaled, you can be infected. There also is some evidence that you might get infected by touching something that has virus on it and then touching your own mouth or nose. A third way to possibly get infected is to inhale dust containing influenza virus. Scientists aren’t really sure which of these ways of spread is the most common. Swine influenza has not been shown to be transmissible to people through eating properly handled and prepared pork (pig meat) or other products derived from pigs.

CDC Assessment

It's possible that sporadic infections and even localized outbreaks among people with this virus will continue to occur. While there is no evidence at this time that sustained human-to-human transmission is occurring, all influenza viruses have the capacity to change and it's possible that this virus may become widespread. So far, the severity of illnesses associated with this virus in people has been similar to the severity of illnesses associated with seasonal flu virus infections. Limited serologic studies indicate that adults may have some pre-existing immunity to this virus while children do not. CDC is closely monitoring human infections with all novel influenza viruses, including H3N2v viruses, and will provide more information as it becomes available.

For more general information about variant influenza viruses, see Variant (Swine Origin) Influenza Viruses in Humans.

For more detailed information about previous cases of H3N2v infection, see Reports of Human Infections with Variant Viruses.

Top