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Notes from the Field: Outbreak of Influenza A (H3N2) Virus Among Persons and Swine at a County Fair — Indiana, July 2012

During July 12–16, 2012, the Indiana State Department of Health and the Indiana Board of Animal Health identified respiratory illness among swine and persons at a county fair held July 8–14. On July 16, specimens were collected from four persons with respiratory illness; two had become ill on July 12 and sought care at an emergency department, and two were identified as part of the subsequent public health investigation. All four persons were swine exhibitors or family members of swine exhibitors and had close contact with swine. On July 18, reverse transcription–polymerase chain reaction testing at the Indiana State Department of Health laboratory identified suspected influenza A (H3N2) variant (H3N2v) virus* in all four specimens. On July 21, partial genome sequencing at CDC confirmed H3N2v virus with the influenza A (H1N1)pdm09 virus M gene; the viruses detected in the four specimens are similar to 12 viruses detected in 2011 and one detected earlier this year (1). None of the four persons were hospitalized, and all have fully recovered.

Additionally, all respiratory specimens collected from a sample of 12 swine at the fair were positive for influenza A (H3N2) virus. The specimens were forwarded to the National Veterinary Services Laboratories of the U.S. Department of Agriculture for additional testing. Preliminary genetic analysis has shown a very high level of similarity between the gene sequences of H3N2v viruses from humans and the H3N2 viruses from swine.

Although human-to-human transmission of H3N2v has been limited in previous outbreaks (1), these viruses could change to transmit efficiently among humans. Clinicians who suspect influenza in persons with recent exposure to swine should obtain a nasopharyngeal swab or aspirate from the patient, place the swab or aspirate in viral transport medium, and contact their state or local health department to arrange transport and request a timely diagnosis at a state public health laboratory (1). Clinicians should consider antiviral treatment with oral oseltamivir or inhaled zanamivir in suspected cases (2). Persons who raise swine or come into close contact with swine at fairs or other venues should be aware of the potential risk for influenza transmission between swine and humans. To reduce this risk, preventive measures such as practicing frequent hand hygiene and respiratory etiquette are recommended. Persons also should avoid close contact with animals that look or act ill, when possible, and if experiencing influenza-like illness themselves, should avoid contact with swine. Additional guidelines on prevention of influenza transmission between humans and swine are available at http://www.cdc.gov/flu/swineflu/industry_guidance.htm.

Including the cases in this report, 17 infections with H3N2v virus with the influenza A (H1N1)pdm09 virus M gene have been reported since August 2011. Novel influenza A virus infection in humans is a nationally notifiable disease (3) and a reportable disease under International Health Regulations (4). State public health laboratories should contact CDC and send all suspected novel influenza A specimens for confirmatory testing. Additional information about H3N2v is available at http://www.cdc.gov/flu/swineflu/influenza-variant-viruses-h3n2v.htm.

Reported by

Shawn Richards, Mark Glazier, Jennifer House, DVM, Pam Pontones, MA, Indiana State Health Dept; Douglas Metcalf, Bret Marsh, DVM, Indiana Board of Animal Health. Sabrina Swenson, DVM, John Korslund, DVM, Animal and Plant Health Inspection Svc, US Dept of Agriculture. Lenee Blanton, MPH, Scott Epperson, MPH, Matthew Biggerstaff, MPH, Lynnette Brammer, MPH, Susan Trock, DVM, Michael Jhung, MD, Joseph Bresee, MD, LaShondra Berman, William Davis, Stephen Lindstrom, PhD, Alexander Klimov, PhD, Daniel Jernigan, MD, Nancy Cox, PhD, Influenza Div, National Center for Immunization and Respiratory Diseases, CDC. Corresponding contributor: Lenee Blanton, lblanton@cdc.gov, 404-639-3747.

References

  1. CDC. Update: influenza A (H3N2)v transmission and guidelines—five states, 2011. MMWR 2012;60:1741–4.
  2. CDC. Antiviral agents for the treatment and chemoprophylaxis of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2011;60(No. RR-1).
  3. Council of State and Territorial Epidemiologists. National reporting for initial detections of novel influenza A viruses. Position statement 07-ID01. Atlanta, GA: Council of State and Territorial Epidemiologists; 2007. Available at http://www.cste.org/ps/2007ps/2007psfinal/id/07-id-01.pdf. Accessed July 24, 2012.
  4. World Health Organization. International health regulations (2005), Second edition. Geneva, Switzerland: World Health Organization; 2008. Available at http://whqlibdoc.who.int/publications/2008/9789241580410_eng.pdf. Accessed July 24, 2012.

* Influenza viruses that circulate in swine are called swine influenza viruses when isolated from swine, but are called variant viruses when isolated from humans. A variant virus (human isolate) might or might not have the M gene from the influenza A (H1N1)pdm09 virus, along with other genetic changes. Seasonal influenza A (H3N2) viruses that circulate worldwide in the human population have significant antigenic and genetic differences from influenza A (H3N2) viruses circulating in swine. Additional information available at http://www.who.int/influenza/gisrs_laboratory/terminology_ah3n2v/en/index.html.


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