June 17, 2019
8 min read

‘Common-sense’ precautions reduce risk for variant flu at fairs

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Influenza seasons are often unpredictable in timing, severity and which virus will predominate. Influenza pandemics, caused by novel viruses, are always unpredictable. The last one, in 2009, marked the emergence of a new influenza A(H1N1) virus — originally called “swine flu” — and the first influenza pandemic in 41 years.

Ten years later, many counties and states are getting ready for annual agricultural fairs, which have been the primary source of variant influenza, a term used to describe human infections with influenza viruses that normally circulate in pigs. The 2009 pandemic was caused by a virus with genes from pigs, humans and birds.

“Swine flu viruses do not normally infect humans. However, sporadic human infections with influenza viruses that normally circulate in swine and not people have occurred,” James C. Kile, DVM, MPH, a public health veterinarian in the CDC’s Influenza Division, explained to Infectious Disease News.

According to James C. Kile, DVM, MPH, only the CDC can confirm if a patient is infected with a variant influenza virus.
Source: CDC.

“Most commonly, human infections with variant viruses have occurred in people exposed to infected pigs — for example, children near pigs at a fair or workers in the swine industry,” Kile said. “In short, it’s possible that pigs at fairs may be infected with a swine influenza virus and that people could get infected if they are exposed to infected swine or to [a] virus-contaminated environment.”

As the agricultural fair season gets underway, Infectious Disease News spoke with Kile and other experts to get a clearer picture of the dangers that variant influenza poses and what measures clinicians should take if they suspect that one of their patients has been infected.

Risk for infection

Swine influenza is caused by influenza A viruses of different subtypes and strains, according to the CDC. The main viruses that circulate in pigs in the United States are swine triple reassortant (tr) H1N1 influenza virus, trH3N2 virus and trH1N2 virus.

“Influenza virus is a common pathogen found in swine, sometimes without clinical signs. Surveys show that 80% or more of the swine population has been exposed to influenza at some time in their lives. So, finding influenza in the swine population at a public exhibition is neither surprising nor alarming by itself,” John Korslund, DVM, staff veterinary epidemiologist with the USDA, told Infectious Disease News. “When one considers the total number of fairs and number of attendees vs. [the] number of reported clinical variant influenza cases, the risk of infection in people appears to be quite low, but not zero.”


In total, the most recent U.S. data show that variant influenza viruses caused 461 reported infections between 2011 and 2018. The highest case count occurred in 2012, with 313 combined cases of H1N1v, H1N2v and H3N2v across 13 states, resulting in 16 hospitalizations and one death.

John Korslund

According to the CDC, variant virus infections typically occur in people exposed to infected pigs, common examples being children and teens exhibiting pigs at fairs or workers in the swine industry who are nearby when an infected pig coughs or sneezes. People may also be infected by touching a contaminated surface and then touching their mouth or nose. The primary source of variant influenza infections every year is exposure to pigs at agricultural fairs, Kile said.

According to Kile, the CDC provides clinical, epidemiologic and laboratory guidance and recommendations to enhance the domestic response to novel influenza viruses.

The agency and state health departments have developed guidance for people who attend fairs, and it has carried out educational efforts to spread the word about the appropriate precautions people should take at fairs and similar settings.

In an effort to reach younger audiences, the CDC worked with the USDA and 4-H to develop and publish a graphic novel last year about a young group of friends who assist officers from the CDC’s Epidemic Intelligence Service (EIS) to investigate their friend Eddie’s illness from a variant influenza virus acquired from his show pig, Hamlet, while attending a fair.

In the story, the virus is described as having “pandemic potential.” Both Eddie and Hamlet recover, but the story ends with one of the friends describing a TV report about more human cases and more infected pigs. “The EIS officers were investigating,” the friend says. “Yeah, I wonder if this is the end of it ...” Eddie replies in the story’s final line.

According to Kile, there have been no reports that human contact with an infected pig at an agricultural fair has ever caused an influenza pandemic, but the potential exists.

“Influenza A viruses are constantly changing, making it possible on very rare occasions for nonhuman influenza viruses to change in such a way that they can infect people” Kile said.

According to the CDC, anyone attending fairs where pigs are present should not eat, drink or put anything in their mouth in pig barns or show arenas; should not take toys, pacifiers, cups, strollers or similar items into these areas; should wash their hands often with soap and water before and after pig exposure; and avoid attending these events if they are sick with influenza-like illness (ILI).


The CDC also recommends that people at high risk for serious influenza complications — including children aged younger than 5 years, people aged older than 65 years, people who are pregnant or those with certain long-term health conditions — avoid pigs and swine barns altogether.

Importance of animal care

According to Korslund, the best defense against variant influenza is to take prevention measures in pigs.

“It starts with educating the pig owners about good stockmanship and animal care, including comfort and vaccination if recommended by a veterinarian,” Korslund said. “Every pig needs to be watched closely for illness every day, with a veterinarian called if a pig appears to be sick.”

Stacy Holzbauer

According to the CDC, just as seasonal influenza vaccines do not always protect humans, swine influenza vaccines are not 100% effective in pigs. Young pigs are generally protected by vaccinating sows, but maternal antibodies are not fully protective and decrease by the time the young pigs are 10 to 13 weeks old or sooner.

Swine producers and handlers work together with a veterinarian to develop management strategies to reduce the emergence and spread of influenza among herds. Local guidelines also aim to prevent the emergence and spread of variant influenza viruses. Swine workers are instructed to watch the animals for symptoms, including loss of appetite and cough, and contact a veterinarian immediately if illness is suspected, according to Kile.

Stacy Holzbauer, DVM, MPH, a deputy state public health veterinarian at the Minnesota Department of Health, noted important research done in Ohio that found that keeping the level of virus low among pigs is imperative.

Andrew S. Bowman, DVM, PhD, MS, assistant professor of veterinary medicine at Ohio State University, and colleagues tested 1,073 pigs exhibited at 53 agricultural fairs in Ohio from 2009 to 2011 for signs of ILI. Influenza A was recovered from pigs at 12 fairs (22.6%) during the 3-year sampling period, but pigs at 10 of those 12 fairs did not show any signs of ILI, demonstrating the risk that subclinical swine influenza may pose to humans, Bowman and colleagues said.

The CDC, USDA and 4-H collaborated on a graphic novel to teach kids about variant influenza.
Source: CDC.

They suggested that one potential strategy to mitigate the risk for intra- and interspecies transmission of influenza A virus at fairs on the swine side is shortening the swine exhibition period.

“Basically, they found that the longer a pig is at the fair, the higher the risk of being exposed to an infected pig and the more likely that pig will become infected and shed the virus,” Holzbauer told Infectious Disease News. “Based on that, there are recommendations that pigs not be at the fair for more than 3 days at a time, decreasing the risks.”

Joni Scheftel

According to the CDC, pigs that test positive for swine influenza at fairs should be isolated immediately. Swine exhibitors are not only instrumental in identifying potentially ill animals but in preventing the spread of influenza by practicing the same care as guests to fairs by not eating or drinking near barns and arenas. Additional measures for handlers include wearing protective clothing, gloves and masks that cover the mouth and nose if a sick pig is present, the CDC says.

The responsibility of keeping animals healthy also falls on fair attendees, according to Joni Scheftel, DVM, MPH, state public health veterinarian supervisor in the Minnesota Department of Health. The CDC recommends that people sick with influenza or who have ILI symptoms avoid contact with pigs to avoid spreading human influenza strains to pigs.

“We give our seasonal influenzas to pigs, and they can get sick from us just like we can get sick from them,” Scheftel said. “If you think about flu as a virus that can infect more than one species, people will realize they may have influenza and can make the pigs sick.”

What should clinicians know?

From 2008 to 2018, the Minnesota Department of Health saw 21 cases of variant influenza. According to Scheftel, case counts over the years have been as high as 10.

“Not all of these cases had contact at fairs,” she told Infectious Disease News. “All were unique in that they did have contact with swine, however. Five were contracted at fairs and were mainly exhibitors, eight were contracted from swine at the live animal markets and five were from people who work on swine farms. One case was from an unknown source, and it is possible that two were from person-to-person contact. That does happen, but it’s very rare.”

According to Holzbauer, Minnesota officials conduct enhanced surveillance around state fair season, paying special attention to members of 4-H and people showing animals at the fairs. Any of these individuals who develops ILI is immediately tested for variant influenza.

“We also do routine surveillance for regular seasonal influenzas and we will pick up cases occasionally through that routine surveillance as well,” Holzbauer said. “Because the viruses do look differently in the lab, they’re easy to flag and we can move quickly.”

According to the CDC, patients who have been infected with variant influenza viruses will have symptoms similar to seasonal influenza, including fever, lethargy, lack of appetite and coughing, or less common symptoms such as runny nose, sore throat, eye irritation, nausea, vomiting and diarrhea.


Kile said only the CDC can confirm if a patient is infected with a variant influenza virus.

“For any ill person with an identified swine exposure in the week prior to illness onset, respiratory samples should be taken for testing,” Kile said. “Clinicians should obtain a nasopharyngeal swab or aspirate — or a combined nasal swab and throat swab — place the swab or aspirate or combined specimen into 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.”

Kile said standard influenza antivirals also can be used to treat variant influenza infections, including the four that are approved for use in the U.S.: baloxavir marboxil, oseltamivir, peramivir and zanamivir. He noted that research into a universal influenza vaccine that would provide long-term immunity against many influenza viruses “is at an early stage,” and it is uncertain whether such a vaccine would protect against variant influenza viruses.


Korslund stressed that animal health officials at local fairs should be notified of any human cases of variant influenza.

“Influenza is a shared animal-human infection, and we all do our best when we share our findings as we diagnose them to further our understanding of these zoonotic outbreaks,” he said.

All in all, experts seem to agree that taking proper precautions can mitigate the risk that fairs pose for outbreaks of variant influenza virus.

“Fairs are a great rural American tradition to be treasured. They are as safe as ever, if everyone takes common-sense precautions regarding sanitation and hygiene,” Korslund said. – by Caitlyn Stulpin

Disclosures: Holzbauer, Kile, Korslund and Scheftel report no relevant financial disclosures.