U.S. Swine Workers at Increased Risk of Infection with Swine Influenza Virus

November 28, 2005

With national attention focused on the avian flu threat, other infections that could be transmitted from animals to people are also coming under scrutiny. People with work exposure to pigs, such as farmers, veterinarians and meat processing workers, are at heightened risk of contracting swine influenza, according to a study in the Jan. 1 issue of Clinical Infectious Diseases, now available online.

Pigs' physical makeup allows them to contract-and to spread-influenza viruses to and from other species, such as humans and birds. Due to their susceptibility to influenza virus infections from other species, pigs can also serve as "mixing vessel hosts" that can produce new influenza virus strains that could pose a risk to human health.

In Iowa, the state with the highest swine production, researchers examined farmers, veterinarians, meat processing workers and a control group of people who had no occupational contact with pigs. They discovered that, of the four groups, farmers were most likely to be seropositive-that is, to have antibodies in their blood against swine influenza, indicating previous infection with the virus. Veterinarians also had increased odds of seropositivity. Meat processing workers had elevated antibody levels as well, though the odds were not as high, perhaps due to the workers' limited exposure to live pigs.

Despite the possibility for human infection with swine influenza, people shouldn't panic, according to authors Gregory Gray, MD, and Kendall Myers, MS, of the University of Iowa. "While severe swine influenza virus infections in humans have been reported, we expect that the normal clinical course of swine influenza infections [in humans] is mild or without symptoms," said Dr. Gray.

Pork consumption shouldn't pose a problem, either. "There's no evidence to suggest that swine influenza can be transmitted to humans through meat," Ms. Myers said, so as long as people cook pork thoroughly and practice good handwashing, then pork chops, bacon and ham can stay on the menu.

Because pigs are susceptible to human infections, both the pork industry and swine workers could benefit from the establishment of a human influenza vaccination program. There is no human vaccine against swine influenza at this point, but increasing surveillance for influenza among swine workers is one key component of helping to prevent an epidemic. "Right now, [swine workers] are not included in the national pandemic plan, nor are they closely monitored for influenza," Dr. Gray said. "Should pandemic influenza virus strains enter the United States and these workers not be given special attention, we think it could be a really big problem for Iowa."

Infectious Diseases Society of America

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