#12,878
Although it hasn't come anywhere near the number of cases reported in 2012 (n=309), 2017 - with 65 novel swine variant virus reports to date - now sits firmly in second place. This week FluView has added three new cases, 1 each from three different states.
The CDC describes Swine Variant viruses in their Key Facts FAQ.
What is a variant influenza virus?
When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus.” For example, if a swine origin influenza A H3N2 virus is detected in a person, that virus will be called an “H3N2 variant” virus or “H3N2v” virus.
Swine variant infections are generally mild or moderate in severity, and are indistinguishable from regular flu without a lab test. Most are linked to direct or indirect contact with swine, often at agricultural exhibits and county fairs.
While H3N2 is the most commonly reported strain, unusually we've seen 4 H1N2 cases this year, which in past years has been the rarest subtype reported. This report from today's FluView, after which I'll return with a bit more.
Novel Influenza A Virus:
Three human infections with novel influenza A viruses were reported by three states (Colorado [1], Nebraska [1], and Michigan [1]) during week 43. Two infections were with influenza A(H3N2) variant (H3N2v) viruses and one infection was with an influenza A(H1N2) variant (H1N2v) virus.
The patient in Colorado reported exposure to swine at an agricultural event during the week preceding illness onset.
The patient in Nebraska reported no contact with swine during the week preceding illness onset, however a member of same household did report exposure to swine.
The patient in Michigan is a close contact of a laboratory-confirmed H3N2v infection that was reported earlier this year. While exposure to swine was reported for the patient, that exposure occurred more than a week preceding illness onset, which is outside of the typical incubation period. It is possible that limited human-to-human transmission occurred.
No ongoing human-to-human transmission has been identified.
A total of 65 variant virus infections have been reported to CDC so far during 2017. Sixty-one of these were influenza A (H3N2) variant (H3N2v) viruses (Delaware [1], Maryland [39], Michigan [2], Nebraska [1], North Dakota [1], Ohio [15], Pennsylvania [1], and Texas [1]) and four were influenza A (H1N2) variant (H1N2v) viruses (Colorado [1] and Ohio [3]). Six of the 65 infections resulted in hospitalization; but all patients recovered.
Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be more fully understood and appropriate public health measures can be taken. Additional information on influenza in swine, variant influenza infection in humans, and strategies to interact safely with swine can be found at http://www.cdc.gov/flu/swineflu/index.htm. .
This isn't the first time we've seen possible human-to-human transmission of these swine variant viruses (see CID Journal: H3N2v Outbreaks In United States – 2012), but so far none of these outbreaks has resulted in sustained transmission.
Although the Public Health risk from these swine variant viruses is considered low at this time, the CDC takes these emerging swine flu viruses seriously, as evidenced by their most recent assessment.
CDC Assessment
It’s possible that sporadic infections and even localized outbreaks among people with this virus may occur. While there is no evidence at this time that sustained human-to-human transmission has occurred, all influenza viruses have the capacity to change and it’s possible that this virus may change and become widespread in people.
Illness associated with H3N2v infection so far has been mostly mild with symptoms similar to those of seasonal flu. Like seasonal flu, however, serious illness, resulting in hospitalization and death is possible.
In 2012, for example, of 309 human infections with H3N2v, 16 people were hospitalized and one of these people died. Most of the people who were hospitalized and the person who died had one or more health or age factor that put them at high risk of serious flu-related complications.
People at high risk of serious complications from seasonal influenza and 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.
CDC has issued guidance for people attending fairs where swine might be present, including additional precautions for people who are at high risk of serious flu complications. Limited serologic studies indicate that adults may have some pre-existing immunity to this virus while children do not. Most cases of H3N2v infection have occurred in children who have little immunity against this virus.
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.
As state and county fair season continues this fall, it would not be unexpected to see additional, scattered reports of swine variant infection, as these venues tend to put a lot of people into close contact with pigs.
For more information on swine variant viruses, and how to protect yourself when in contact with farm animals, the CDC provides the following guides.
- Key Facts for People Exhibiting Pigs at Fairs[545 KB, 2 pages]
- Take Action to Prevent the Spread of Flu Between People and Pigs[1.3 MB, 2 pages]
- Educational Posters[389 KB, 1 page]
- Compendium of Measures to Prevent Disease Associated with Animals in Public Settings, 2013.
- Reduce Your Risk (English)[22 KB, 1 page] | (Spanish)[22 KB, 1 page]
- Measures to Minimize Influenza Transmission at Swine Exhibitions, 2016 – NASAHO and NASPHV[97 KB, 8 pages]
