With 16 new human cases in the last three weeks -- 12 in the last week alone -- an outbreak of a variant strain of swine flu is giving CDC officials the jitters.

What worries officials is that the new flu, officially called variant type A H3N2 or H3N2v, carries the M gene from the human H1N1 pandemic flu bug. This gene makes it easier for flu bugs to infect humans and spread among them.

The first human case was detected in July 2011. Since then there have been 29 reported cases, although more cases likely have gone unreported.

"Since the fall of 2011 there has been a big increase in these types of infections," Joseph Bresee, MD, of the CDC's Influenza Division, said at a news conference held to announce the new cases. "All 29 cases have had H3N2v with the M gene of pandemic H1N1. This may confer increased transmissibility to and among humans."

Last year, three people caught the bug from another person. As far as the CDC can tell, that hasn't happened this year. And there's been no sustained spread of the new swine flu bug among people.

All the cases so far had contact with pigs. Most cases have been children who came into contact with infected pigs at state fairs. Ten of this week's new cases were in Ohio. One was in Indiana and another was in Hawaii.

According to Lisa Ferguson of the USDA, the virus has been detected in pigs in 11 states.

Flu is common among pigs, and every year a few people catch a swine flu bug. But this new swine flu looks different.

"We have detected cases of this virus with increasing frequency," Bresee said. "We expect further cases of human infection, either with contact with swine or from limited human-to-human spread. We expect some of the cases will be severe."
H3N2v Swine Flu Symptoms

Fortunately, the new flu hasn't been more serious than seasonal flu. The symptoms are the same: fever, cough, sore throat, muscle aches, and headaches. Everyone infected so far this year got better without having to be hospitalized. Last year there were three hospitalizations, all in people with underlying conditions known to increase risk of severe flu. There have been no deaths.

Current flu drugs should be just as effective against the new swine flu as against seasonal flu. However, current flu vaccines do not protect against the new swine flu. A vaccine has been produced, and Bresee says it soon will be tested in clinical trials.

Is this the beginning of a new flu pandemic? Maybe. Maybe not. Flu is among the most unpredictable of viruses. H3N2v could become a pandemic virus this year, in 20 years, or never.

"The key point is this is still a swine virus -- maybe a little different, but still not a human virus," Bresee said. "This virus is different because it acquired the M gene from pandemic virus, and that may confer an advantage to spreading among humans. But whether we're seeing more cases because of this, or because it's the season for state fairs and we're looking more closely, we don't know."

The CDC wants to know more about the new swine flu. People who get sick after contact with pigs are urged to see a doctor, and doctors are urged to collect patient samples for further tests at CDC.
How to Avoid Swine Flu

Because it's now state fair season, when many people are exposed to farm animals, the CDC is issuing special advice:

    If you are pregnant, frail, have a weakened immune system, or have any other risk for severe flu, consider skipping the state fair this year.
    Wash your hands with soap and water before AND after exposure to animals.
    Don't carry food or beverages into areas where there are animals.
    Don’t eat or drink in areas where there are animals.

Although a person can get swine flu from contact with live pigs, the disease is not spread by eating or preparing pork.