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Infections linked to pig exposure at two different agricultural fairs in Michigan
August 4, 2023—CDC this week reported the first two U.S. human infections with swine flu viruses in 2023. These human infections were caused by two different types of flu viruses that normally spread among pigs, and they occurred in two people who attended different agricultural fairs in Michigan and had exposure to pigs. CDC recommends people take precautions to prevent the spread of swine influenza viruses to people and has guidance for people exhibiting pigs at fairs, people attending fairs, and fair organizers.
Every year, there are rare sporadic human infections with flu viruses that usually spread in pigs. When found in people, these are called “variant flu virus” infections and designated with the letter “v” after the subtype. Variant flu virus infections are usually associated with contact with pigs, often at agricultural fairs. While infections with swine influenza viruses usually cause mild illness, they are concerning because they can cause severe illness, especially in people at higher risk of serious flu complications, and because of their pandemic potential. These infections are fully investigated to be sure that such viruses are not spreading in an efficient and ongoing way in people and to limit further exposure of people to infected animals if infected animals are identified.
Presumptive positive influenza A(H3)v virus infection
The Michigan Department of Health and Human Services first reported a presumptive positive influenza A(H3) variant virus infection on July 26 in a person who attended a fair that took place July 7-16. A respiratory specimen from that patient was sent to CDC and received on July 27. Diagnostic testing conducted at CDC was inconclusive, likely due to the respiratory specimen not containing enough virus. However, it is likely the patient was infected with an influenza A(H3)v virus given the presumptive positive test results from Michigan, as well as the epidemiologic findings of the local investigation.
An investigation into this first infection found that:
The Michigan Department of Health and Human Services notified CDC of a specimen that tested positive for influenza A but lacked reactivity with diagnostic tests for contemporary human influenza viruses representing either H1pdm09 or H3 subtypes on July 31. A respiratory specimen from that patient was sent to CDC and received on August 2. This was confirmed at CDC to be an influenza A(H1N2)v virus infection. This occurred in a person who attended a different fair, which took place July 23-29.
An investigation into the second infection found that:
Agricultural fairs take place across the United States every year, primarily during the summer months and into early fall. Many fairs have swine exhibitions, where pigs from different places come into close contact with each other and with people. These venues can increase the risk that flu viruses will spread among pigs and between pigs and people. ...
August 4, 2023—CDC this week reported the first two U.S. human infections with swine flu viruses in 2023. These human infections were caused by two different types of flu viruses that normally spread among pigs, and they occurred in two people who attended different agricultural fairs in Michigan and had exposure to pigs. CDC recommends people take precautions to prevent the spread of swine influenza viruses to people and has guidance for people exhibiting pigs at fairs, people attending fairs, and fair organizers.
Every year, there are rare sporadic human infections with flu viruses that usually spread in pigs. When found in people, these are called “variant flu virus” infections and designated with the letter “v” after the subtype. Variant flu virus infections are usually associated with contact with pigs, often at agricultural fairs. While infections with swine influenza viruses usually cause mild illness, they are concerning because they can cause severe illness, especially in people at higher risk of serious flu complications, and because of their pandemic potential. These infections are fully investigated to be sure that such viruses are not spreading in an efficient and ongoing way in people and to limit further exposure of people to infected animals if infected animals are identified.
Presumptive positive influenza A(H3)v virus infection
The Michigan Department of Health and Human Services first reported a presumptive positive influenza A(H3) variant virus infection on July 26 in a person who attended a fair that took place July 7-16. A respiratory specimen from that patient was sent to CDC and received on July 27. Diagnostic testing conducted at CDC was inconclusive, likely due to the respiratory specimen not containing enough virus. However, it is likely the patient was infected with an influenza A(H3)v virus given the presumptive positive test results from Michigan, as well as the epidemiologic findings of the local investigation.
An investigation into this first infection found that:
- The patient was exposed to pigs within 10 days prior to illness onset at an agricultural fair where swine influenza A virus was detected among pigs.
- The patient was treated with flu antivirals.
- The patient was not hospitalized and has recovered from their illness.
- Additional investigation did not identify respiratory illness in any of the patient’s close contacts or household contacts.
- To date, no person-to-person spread of this virus has been identified.
The Michigan Department of Health and Human Services notified CDC of a specimen that tested positive for influenza A but lacked reactivity with diagnostic tests for contemporary human influenza viruses representing either H1pdm09 or H3 subtypes on July 31. A respiratory specimen from that patient was sent to CDC and received on August 2. This was confirmed at CDC to be an influenza A(H1N2)v virus infection. This occurred in a person who attended a different fair, which took place July 23-29.
An investigation into the second infection found that:
- The patient was exposed to pigs within 10 days prior to illness onset at another agricultural fair.
- The patient was treated with flu antivirals.
- The patient was not hospitalized and is recovering from their illness.
- Additional investigation did not identify respiratory illness in any of the patient’s close contacts or household contacts.
- To date, no person-to-person spread of this virus has been identified.
Agricultural fairs take place across the United States every year, primarily during the summer months and into early fall. Many fairs have swine exhibitions, where pigs from different places come into close contact with each other and with people. These venues can increase the risk that flu viruses will spread among pigs and between pigs and people. ...
