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"Swine Flu in U.S., Mexico Lung Illness Heighten Pandemic Risk

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learn how to protect yourself in a pandemic

April 24, 2009
By Jason Gale and Tom Randall
Bloomberg

"Disease trackers are asking U.S. hospitals to help follow a new strain of swine flu and are trying to determine whether it’s related to hundreds of illnesses and 57 deaths in Mexico.

A previously unseen variant of H1N1 swine influenza has sickened at least seven people in California and Texas, the Atlanta-based U.S. Centers for Disease Control and Prevention said yesterday. The World Health Organization said 57 people died among more than 800 in the Mexico City region who developed flu-like symptoms in the past month.

Global health experts are studying whether the U.S. and Mexico illnesses pose a threat of pandemic, according to the European Centre for Disease Prevention and Control. U.S. hospitals today were asked to collect samples from patients with flu-like symptoms, said William Schaffner, a flu expert at Vanderbilt University School of Medicine in Nashville, Tennessee.

“This has a sense of urgency about it,” Schaffner, chief of preventive medicine at Vanderbilt, said in a telephone interview today. “They are asking us who work in hospitals to go to our emergency rooms and our pediatric wards to gather specimens and start testing them.”

Investigators haven’t found a link between the California and Texas cases, indicating the virus may be circulating elsewhere, Schaffner said. CDC disease experts will continue investigating whether the outbreaks have a common source, he said. The agency also will host a conference call today with experts, he said.

Threat of Pandemic

Flu can spread quickly when a new strain emerges, because no one has natural immunity. The so-called 1918 Spanish Flu pandemic, which may have killed as many as 50 million people, began when an avian flu virus jumped to people, experts said.

“We are taking this very seriously,” Gregory Hartl, spokesman for WHO, the Geneva-based United Nations agency, said in a telephone interview today. “We have to get laboratory confirmation of what it is. We need to know how widespread it is.” The Mexico illnesses are affecting “otherwise healthy adults,” Hartl said.

Pandemic Potential

“The infection of humans with a novel influenza-A virus infection of animal origins, as has happened here, is of concern because of the risk, albeit small, that this could represent the appearance of viruses with pandemic potential,” the European Centre for Disease Prevention and Control, based in Stockholm, said in a statement.

There’s no evidence a pandemic strain is evolving in the U.S., the European agency said. The CDC reached the same conclusion.

“We don’t think this is a time for major concern,” Anne Schuchat, CDC’s director of respiratory diseases, told reporters on a conference call yesterday.

Authorities in Mexico asked the Public Health Agency of Canada to help identify what’s causing the lung infection that has also spread to five health-care workers, the Ottawa-based agency said in an e-mail yesterday. Mexico Health Minister Jose Cordova canceled classes in Mexico City today and recommended citizens avoid public places.

Canada’s National Microbiology Lab received 51 specimens from Mexico on April 22 and will test them for pathogens. Tests in Mexico found patients had the H1N1 and type-B influenza strains and the parainfluenza virus, the agency said.

Pigs Susceptible

Three main human flu strains -- H3N2, H1N1 and type-B -- cause 250,000 to 500,000 deaths a year globally, according to the World Health Organization, a United Nations agency. Pigs also are susceptible to flu, including the H1N1 subtype.

“It will be critical to determine whether the strains of H1N1 isolated from patients in Mexico are also swine flu,” Donald Low, an infectious diseases specialist at Toronto’s Mount Sinai Hospital, told the Canadian Press.

The CDC is discussing its cases and viruses with Mexico and the Pan American Health Organization, Schuchat said.

“At this point, we do not have any confirmation of swine influenza in Mexico,” Schuchat said.

Symptoms of the illnesses in Mexico include high fever, headache, eye pain, shortness of breath and extreme fatigue with rapid progression of symptoms to severe respiratory distress in about five days, the Canadian agency said. A “high proportion” of cases require mechanical respiration, it said.

U.S. Sickness

The four males and three females in San Diego County and Imperial County, California, and in San Antonio, diagnosed with swine flu had mild flu-like symptoms. The patients, 9 to 54 years old, included a father-daughter pair and two boys attending the same Texas school.

The virus is contagious and spreading from human to human, the CDC said in a statement on its Web site. The patients began feeling sick from March 28 to April 19. All have recovered and only one was hospitalized, according to the CDC. None had direct contact with pigs.

“That’s unusual,” Schuchat said. “We don’t know yet how widely it’s spreading and we certainly don’t know the extent of the problem.”

As precaution, CDC is preparing the virus as a vaccine seed strain that could be used to make immunizations, she said.

The swine flu virus contains four different gene segments representing both North American swine and avian influenza, human flu and a Eurasian swine flu, CDC said.

Not Seen Before

“We haven’t seen this strain before, but we haven’t been looking as intensively as we are these days,” Schuchat said. “It’s very possible that this is something new that hasn’t been happening before.”

Swine influenza is a respiratory disease of pigs caused by type-A influenza that regularly causes outbreaks among the animals, according to the CDC. Swine flu doesn’t normally infect people, though human infections do occur and cases of human-to- human spread of swine flu viruses have been documented.

Infection in pigs is regarded as especially problematic because of the risk of “reassortment” to produce a new virus, the European Centre for Disease Prevention and Control said.

“These mild U.S. cases infected with a novel influenza are not reflecting the emergence of a pandemic strain, but they at least raise the possibility that there has been limited human- to-human transmission,” the health agency said."

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