(Updated Aug 11: CDC has raised the number of people confirmed infected to 153)

As many as 153 people have been infected this summer with a new pig flu virus, the U.S. Centers for Disease Control and Prevention said this week, although the disease does not appear to be any more serious than normal seasonal flu. Nine out of 10 of them are children, CDC says.

Most cases appear to be among people who were showing pigs, or people visiting fairs and other places where these pigs are, CDC says. This suggests they are catching the flu directly from infected pigs. So far everyone has gotten better on their own, Dr. Joseph Bresee, from the CDC's influenza division, told reporters on a telephone briefing Thursday.

“At this point there is no evidence of sustained, efficient human to human spread,” Bresee said. “This is not a pandemic situation.”

But Bresee cautioned that even seasonal flu can kill people and this is likely the case with the new form of flu, which is designated H3N2v.

The new strain of H3N2 was first seen last year, and three people were confirmed to have caught the bug from other people. So far it has not been any more serious than regular, seasonal flu, causing fever, a sore throat and achy muscles. Last year no one ended up in the hospital with the new flu. This year, two people have but they are fine now, Bresee said.

While the current flu vaccine does not protect against this new virus coming straight from pigs to people, patients can be treated with the two drugs that work against seasonal flu – Tamiflu and Relenza.

Most of the cases have been in Indiana, where 120 have been reported, the CDC said. There have also been 31 cases in Ohio, one case in Hawaii and one case in Illinois.

Flu viruses have eight genes, and this one is seven-eighths pig virus -- a virus designated H3N2 that’s been circulating among swine for years. But one single gene comes from the H1N1 swine flu virus that caused a new pandemic of influenza  among people in 2009 and which is now part of the human seasonal flu mix.

The names can be confusing because there's also an H3N2 virus that causes seasonal flu in people, and it's one of the three strains of flu virus that is included in the vaccine that's just arriving in doctor's offices and clinics now. "Get your flu vaccine," Bresee advised. "Everybody should get a flu vaccine this year in the U.S. because regular, seasonal flu will be here soon."

CDC stressed that only people who have contact with pigs are at any real risk of catching this flu. "This time of year is the time when you have state and county fairs…there’s thousands of them," Bresee said. CDC has some simple advice to prevent infection:

• Wash your hands after you've been near any live pigs
• Don't bring any food or drink into areas where live pigs are
• Stay away from swine if you are at high risk from flu, for instance if you are elderly or have a weakened immune system.

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A transmission electron micrograph shows some of the structural details of the H3N2 flu virus that infected patients in Indiana and Pennsylvania earlier this year. The virus was formed through the reassortment of two other flu viruses.

Three children in Iowa have come down with a new type of flu virus previously linked to pigs, but this time the bug appears to have been spread by people.

The children, who live in rural Webster and Hamilton counties, did not become seriously ill, said Dr. Patricia Quinlisk, medical director for the Iowa Department of Public Health. But the detection of the virus known as swine-origin A/H3N2 in patients who hadn't had contact with animals raises concerns about potentially greater spread of a new type of flu.

"We have pretty good evidence of person-to-person spread," Quinlisk said. "None of the children or anyone around them had exposure to swine, turkeys or other sources."

Officials with the Centers for Disease Control and Prevention had previously detected seven cases of people with the new H3N2 virus that appears to have acquired a gene that may make it more transmissible from H1N1, the flu that sparked the so-called swine flu pandemic in 2009. Flu viruses often swap genetic parts. Officials say the new virus was probably formed when a pig became infected with the H3N2 virus and the H1N1 virus at the same time.  

The new bug has components of human, avian, H1N1 and swine flu viruses, all mixed together in what scientists call a recombinant virus.

The first new H3N2 case was identified in a child in Indiana in July, and has been followed by cases in Pennsylvania, Maine and, now, Iowa.

In the previous cases, however, the patients either had direct exposure with pigs, or exposure to a person who'd been around pigs. In the new cases, it appears that one of the children transmitted the flu to the other two, and none of them had any animal exposure, Quinlisk said. She declined to identify the children or their ages, saying only they were younger than 18. No further cases have been identified in the past week, she said.

The Iowa cases are nothing to panic about, health officials emphasized. The H3N2 flu causes symptoms similar to the regular seasonal flu, including fever, cough, fatigue, body aches and loss of appetite. 

"People need to be most concerned about the regular, everyday seasonal flu," Quinlisk said.

But Iowa health officials are now testing samples of people with flu-like illness to detect further spread of the new bug. And CDC officials have asked states across the country to be vigilant in looking for it, said Dr. Joe Bresee, the agency's influenza and epidemiology branch chief.

The current seasonal flu vaccine being offered by doctors and clinics was not developed to protect against the H3N2 virus. It contains some antigens similar to a flu virus that circulated in the 1990s, so some people who had the flu then or were vaccinated could have some immunity, but it's not clear how much, Quinlisk said. The Iowa children apparently had not been vaccinated, she added.

With the new cases, CDC officials have confirmed 31 cases in the U.S. of the new swine-origin virus since 2005, including 10 with the H3N2 virus that carries the M gene from the 2009 H1N1 virus.

The best prevention for the new flu, as with any flu, is to wash hands frequently, cover coughs and sneezes and limit spread of germs by staying home when you're sick, health officials said.

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