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University of Iowa News Release

Nov. 22, 2005

U.S. Swine Workers At Increased Risk Of Infection With Swine Influenza Virus

With national attention focused on the avian flu threat, other infections that could be transmitted from animals to people (known as zoonotic illnesses) 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 researchers in the University of Iowa College of Public Health.

Led by Kendall Myers, a doctoral student in occupational and environmental health, and Gregory Gray, UI professor of epidemiology, the 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 swine influenza 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.

The study is published in the Jan. 1, 2006, issue of the journal Clinical Infectious Diseases, now available online at

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 may also serve as "mixing vessel hosts" that can produce new influenza virus strains.

If the H5N1 avian influenza virus or another pandemic strain enters the United States and infects swine herds or poultry flocks, Iowa's 200,000 swine workers and their poultry worker counterparts may be some of the first to be infected, according to the researchers. Iowa is the nation's leading swine-producing state, with more than 9,000 farms raising 25 million hogs per year. 

Because pigs are susceptible to human infections, the pork industry could benefit from the establishment of a human influenza vaccination program for swine workers. The researchers are also concerned, though, for the wellbeing of those who work with swine.

"We're really concerned about agricultural workers and their health," Gray said. "We want to make sure that whatever we can to do protect them is done."

There is no human vaccine against swine influenza at this point, but increasing surveillance for influenza both the human and the zoonotic forms among swine workers is one key component of helping to prevent a pandemic. "Right now, [swine workers] are not included in the national pandemic plan nor are they closely monitored for influenza," 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."

Despite the possibility for human infection with swine influenza, people shouldn't panic, according to the study authors. "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," Gray said.

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

STORY SOURCE: University of Iowa College of Public Health Office of Communications, 4257 Westlawn, Iowa City, IA 52242.

MEDIA CONTACT: Debra Venzke, 319-335-9647,; Writer: Jennifer Larson Martin