Swine influenza infections generally produce mild or no symptoms in both pigs and humans. However, exposure to swine flu virus at a 1988 Wisconsin county fair resulted in serious illness for 50 swine exhibitors and three of their family members; one previously healthy woman who became infected died.

The U.S. swine industry, which employs about 575,000 people, has shifted during the past 60 years from primarily small herds located on family farms to large herds maintained in expansive but confined agricultural facilities. Crowded conditions coupled with the constant introduction of young pigs to existing herds have made swine flu infections among pigs a year-round occurrence rather than the seasonal event they once were. As a result, there is a constant opportunity for people who are occupationally exposed to pigs to become infected with influenza viruses and, conversely, a continual opportunity for human flu viruses to mix with swine or bird flu viruses.

To determine the prevalence of swine influenza infection among swine-exposed employees, the researchers, led by Dr. Gray and graduate student Kendall P. Myers, examined serum samples taken from four adult populations in Iowa between 2002 and 2004. Three populations were occupational groups exposed to pigs: 111 farmers, 97 meat processing workers and 65 veterinarians. The fourth control group included 79 volunteers from the University of Iowa with no occupational pig exposure.

The researchers tested the serum samples for antibodies to several then-current swine and human influenza A viruses. The results showed that all three occupational study groups had markedly elevated antibodies to swine flu viruses compared with the control group. Farmers had the strongest indication of exposure to swine flu viruses, a
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Contact: Kathy Stover
kstover@niaid.nih.gov
301-402-1663
NIH/National Institute of Allergy and Infectious Diseases
28-Nov-2005