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While we continue to be focused primarily on avian flu this summer, since 2010 we've seen more than 500 scattered reports of infection with swine variant influenza viruses (H1N1v, H1N2v & H3N2v) around the nation, often associated with agricultural exhibits at county and state fairs.
Prior to 2016, the H1N2v subtype was only rarely reported (n=7), but since then it has been appearing with increasing frequency (n=41). Last June, in Nature Comms: Potential Pandemic Risk of Circulating Swine H1N2 Influenza Viruses, we looked at growing concerns over this subtype.Two weeks ago we saw two cases of H3N2v reported from Colorado and Michigan, while earlier this year we saw 3 cases of H1N2v (all from Pennsylvania).
Swine variant influenza infections are indistinguishable from seasonal flu without highly specialized testing, which few countries tend to do. Even here in the United States it is assumed we only detect a small percentage of cases (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012)).
Today the CDC is reporting 2 more swine variant cases (1 H1N1v from Ohio & 1 H1N2v from Pennsylvania) - both in people < 18 who had exposure to swine. Both were briefly hospitalized, but have been released.
Novel Influenza A Virus:Surveillance Methods | FluView Interactive
Two human infections with novel influenza A viruses were reported to CDC this week. One infection with an influenza A(H1N1) variant (A(H1N1)v) virus was reported by the Ohio Department of Health and one infection with an influenza A(H1N2)v was reported by the Pennsylvania Department of Health. Both patients are >18 years of age, and developed symptoms and sought healthcare during the week ending August 10, 2024 (Week 32). Both patients were briefly hospitalized due to underlying medical conditions and have since recovered. Investigation by Ohio public health officials found the Ohio patient had exposure to swine at an agricultural event prior to the patient’s illness onset. Investigation by Pennsylvania public health officials found the Pennsylvania patient had occupational exposure to swine. No symptoms were reported among close contacts of either case after the cases’ symptom onset, and no human-to-human transmission related to these cases has been identified.
No new human infections with highly pathogenic avian influenza A(H5N1) virus were reported during Week 33. An ongoing outbreak of H5N1 continues in domestic dairy cattle and poultry, and monitoring for additional cases is ongoing.
A total of seven variant influenza cases have been reported during the 2023-2024 season (four A(H1N2)v, two A(H3N2)v, and one A(H1N1)v). Thirteen cases of human infection with influenza A (H5) have been reported this season, for a total of 20 novel influenza A cases reported during the 2023-2024 season.
When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant” influenza virus. Most human infections with variant influenza viruses occur following exposure to swine, but human-to-human transmission can occur. It is important to note that in most cases, variant influenza viruses have not shown the ability to spread easily and sustainably from person to person.
Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be understood, and appropriate public health measures can be taken.
Additional information on influenza in swine, variant influenza virus infection in humans, and guidance to interact safely with swine can be found at www.cdc.gov/flu/swineflu/index.htm.
Additional information regarding human infections with novel influenza A viruses:
While most fairs have requirements the screening and barring of `sick pigs' from exhibition, over the years we've learned that many pigs may be infected asymptomatically (see EID Journal: Flu In Healthy-Looking Pigs and Transmission Of Swine H3N2 To Humans At Agricultural Exhibits - Michigan & Ohio 2016).
Although the public health risks are considered low, the CDC advises those who are at higher risk of serious flu complications (including children under 5, adults over 65, pregnant women, and those with certain chronic medical conditions), to avoid pigs and the swine barn altogether.
Last year the CDC held a webinar for clinicians on recognizing, treating, and reporting zoonotic influenza cases in the community (see COCA Call : What Providers Need to Know about Zoonotic Influenza), which remains available on their website.
