Pig enclosures stand empty at the Indiana State Fairgrounds. Health officials… (Matt Dial, Associated Press )
A new type of swine flu has infected at least 145 people, mostly children, since July 12, according to the Centers for Disease Control and Prevention. That's a significant jump from the 12 cases confirmed by the agency last week.
"We're seeing a big increase, and we think it's a real increase," said the CDC's Dr. Joseph Bresee in a Thursday update on the virus, which people have contracted after contact with pigs at county fairs.
So far, most of the illnesses have been mild: Two people have been hospitalized this year and nobody has died. Still, CDC officials advise anyone planning to attend an agricultural fair to take precautions.
Here are some facts about the new flu.
What is it and where does it come from?
Influenza A H3N2v is a virus native to pigs that is showing up increasingly in people. As of Thursday, human cases were confirmed in Indiana, Ohio, Illinois and Hawaii.
In healthy people not at high risk for complications, H3N2v resembles a typical flu — causing fever, aches, sore throat, runny nose, sneezing and coughing. Most people recover within a few days on their own. In rare, severe cases, treatment with antiviral drugs is effective.
How do people catch it?
Human cases this year have occurred after exposure to infected pigs, the CDC reported. When a sick pig sneezes or coughs, it spews virus-infested droplets into the air and onto surfaces that can find their way to people.
H3N2v has mostly spread at agricultural fairs, which are common this time of year. They offer prime conditions, said Richard Webby, a flu researcher at St. Jude Children's Hospital in Memphis, Tenn.
"You bring together these fair pigs. I'd assume a lot are not vaccinated.... You get this burst where the virus transmits rapidly among pigs," he said. "At the same time, you're getting more people walking through the barns than you would in a commercial farm."
People do not get H3N2v from eating pork products.
More than 90% of the people infected so far this year have been children. Why?
Often, children are the ones bringing pigs to agricultural fairs and caring for the animals, Bresee said.
Also, about 30% of U.S. adults seem to have antibodies that protect against H3N2v, he added. That's probably because another H3N2 virus circulated in humans in the late 1980s and early 1990s.
Later, the virus returned to pigs, where it traded genetic material with other flu viruses. A new version of this flu emerged again in humans as H3N2v.
Can H3N2v infect animals other than pigs?
Birds, seals, dogs and horses are all susceptible to flu viruses. But Bresee said it is unlikely that this virus is currently spreading in other animals.
"Most flu viruses tend to stay in the animals they're adapted for. Swine flu tends to stay in pigs," he said.
How did H3N2v make the jump to people?
Possibly because of a genetic change it picked up from 2009's pandemic H1N1 influenza, Webby said. This so-called M gene may influence the virus' ability to infect and spread among humans.
Typically, flu experts would expect two or three human cases a year of this type of illness. The "sheer numbers" in the current outbreak give researchers pause, Webby said.
The CDC is closely monitoring the spread of H3N2v and expects more cases in coming weeks — including cases of human-to-human transmission, Bresee said.
Will this year's seasonal flu vaccine protect from this virus?
No. Though this year's vaccine contains a version of H3N2, it isn't the same bug. H3N2v is more closely related to a strain of swine flu that was common in humans around 1995, said Webby.
Bresee stressed that everyone should still get a flu shot this fall, noting that between 5% and 15% of the U.S. population gets sick with seasonal flu each year and 40,000 to 50,000 die from it.
If a flu shot won't protect me from H3N2v, what can I do to prevent infection?
If you're not planning to attend an agricultural fair in coming weeks, you don't need to adjust your behavior, Bresee said. If you are, be sure to wash your hands after contact with swine, avoid eating in animal pens and stay away from pigs that are sneezing, coughing or listless.
The Los Angeles County Fair, scheduled to begin later this month in Pomona, provides hand-washing stations throughout the grounds and veterinary checks for animals before and during the event, said Fairplex spokesperson Leslie Galerne-Smith.
Fairgoers don't bring their own livestock in for competitions, Galerne-Smith added, so all the animals on the grounds are vetted by fair organizers.
People at high risk of complications from flu, including the elderly and people with compromised immune systems, might want to avoid contact with fair pigs altogether, the CDC recommended.