Recent Swine Influenza Detections Associated with Agricultural Fairs, 2023
Nicole Parker-Strobe, MPH I Region 2N Epidemiologist
Melanie Perry, MPH I Region 3 Epidemiologist
On July 16, 2023, the Oakland County Health Division (OCHD) was notified that six pigs at the Oakland County Fair tested positive for Influenza A at the Michigan State University Veterinary Diagnostic Laboratory (MSU VDL). OCHD worked with the fair organizers to obtain contact information for exhibitors and staff who were in the swine barn from July 7-16. The Outbreak Management System (OMS) was utilized to organize, standardize, and record interview data obtained from the exhibitors and their household contacts. Out of 96 exhibitors and fair staff, 85 (89.5%) completed an initial interview with OCHD staff. Among those, 13 individuals (16%) reported developing influenza-like symptoms (e.g., fever, cough, runny nose, fatigue) after attending the fair. Six of these illnesses were ruled out by a negative influenza test, five declined testing, and one had a rapid influenza A positive result but declined further evaluation to confirm and determine if it was of swine origin. One ill exhibitor from Lapeer County was presumptively positive for influenza A H3v at the Michigan Department of Health and Human Services Bureau of Laboratories (MDHHS BOL) on July 26. Confirmatory testing at the Centers for Disease Control and Prevention (CDC) was inconclusive, likely due to the specimen not containing enough virus. However, it is likely the exhibitor was infected with swine influenza given the presumptive A(H3)v result, clinically compatible symptoms, and known exposure to infected pigs. Confirmatory influenza strain subtyping on the ill pigs from the Oakland County fair is pending at the Ames, Iowa National Veterinary Services Laboratories (NVSL) as of August 14, 2023.
On July 30, 2023, a Tuscola County resident presented at an Emergency Department (ED) with influenza-like symptoms after attending the Tuscola County Fair on July 26 and walking through the animal barns. The ED contacted the Michigan Department of Health and Human Services (MDHHS) to arrange for specimens to be submitted to the BOL. The specimens tested positive for influenza A but lacked reactivity with diagnostic tests for contemporary human influenza viruses representing either H1pdm09 or H3 subtypes. The remaining sample was forwarded to CDC where further testing confirmed the presence of Influenza A H1N2v.
Based on the positive result, the Tuscola County Health Department (TCHD) and MDHHS public health staff initiated contact follow up efforts with exhibitors and close contacts associated with the swine barn. Interviews were conducted using the Outbreak Management System (OMS) using a modified questionnaire based on the tool initially developed for the Oakland County Fair investigation. Outreach initially started with 61 identified contacts. Monitoring is ongoing and approximately 130 contacts have been identified to-date. Among these contacts,12 individuals reported influenza-like symptoms. Of those, two have self-reported testing negative for influenza, one has submitted a sample for testing results are pending, and the other nine individuals have declined testing.
The use of the OMS to manage contact follow up for these two response efforts assisted in assuring that those who exhibited or worked at the fair were quickly notified of the potential exposure and directed to appropriate follow-up care as needed. Additionally, as the OMS can manage multiple contacts associated with a defined exposure event, the associated outbreak-specific questionnaires provide a standardized format for data collection and analysis. All MI local health departments, Regional Epidemiologists, and MDHHS staff have access to OMS, which allows for efficient and secure inter-jurisdictional contact sharing.
Contact follow-up after known exposures to ill pigs or swine variant influenza positive individuals is crucial to understanding the emergence, transmission potential, and severity of this zoonotic illness and to preventing additional disease occurrence. Agricultural fairs present an opportunity for further transmission of variant influenza strains amongst exhibited swine and increased human contact with ill pigs. These variant influenza infections in humans are typically mild but can progress to severe illness in those who are at higher risk for influenza complications. Additionally, repeated exposure of swine strain influenza to humans increases the pandemic potential of this virus. Measures can be taken to limit exposure to swine influenza at fairs, creating a safer experience for both the animals and humans. Information on the cases discussed above along with recommendations on how to limit exposures at agricultural fairs is available on the Centers for Disease Control and Prevention's (CDC) Swine Flu News & Spotlights.
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