Officially called H1N1, the virus is probably circulating in “virtually all” U.S. states, Anne Schuchat of the U.S. Centers for Disease Control and Prevention said yesterday. First reported in the U.S. and Mexico, H1N1 also has been confirmed in Central America, Europe, the Middle East, Asia and New Zealand.
Declaration of a pandemic is imminent, the World Health Organization said over the weekend. Globally, health officials have said they’re bracing for the possibility of the disease worsening even as Mexico’s health minister yesterday said the outbreak there was declining. Mexico has been hardest hit, saying it’s had 590 infections and 22 deaths.
“We’re not out of the woods yet,” said Schuchat, interim deputy of the CDC’s science and public health program, in referring to the U.S. outbreak. “I do expect more cases, more severe cases, and I do expect more deaths.”
Schuchat said that she was “particularly concerned” about what will happen when the flu season starts for the Northern Hemisphere. That usually coincides with the fall, around late September, the CDC said on its Web site.
Mexican Outbreak
Mexico’s outbreak probably peaked last week and patients are responding well to antiviral treatments, Health Minister Jose Cordova said yesterday. The virus has been confirmed in 23 of Mexico’s 31 states and the capital district.
“Mexico is trying to return to normalcy as soon as possible,” President Felipe Calderon said late yesterday, adding that it was too soon to tally the economic cost. “We are going to win this battle.”
Still, Margaret Chan, director-general of the World Health Organization, warned that the declining mortality rate from the flu in Mexico didn’t mean the threat of a pandemic had subsided, the Financial Times reported, citing Chan. The virus may return “with a vengeance,” Chan said, according to the report.
The U.S. CDC reported 226 cases in 30 U.S. states, with one death, a 22-month-old child who had traveled from Mexico and died April 27 at a Houston hospital. The number of people with flu in the U.S. is increasing at a time when the typical season would be at its end, Schuchat said.
Spreads Easily
“It does spread very easily,” Richard Besser, the acting head of the CDC, said in an interview on ABC News yesterday. “The word out of New York City where they had a school cluster is it spread very rapidly through that school. But what they were seeing was disease that was not that severe, and when it transmitted to people in the families, they were seeing disease that was not that severe, and that’s encouraging.”
The WHO, a Geneva-based agency of the United Nations, today added Colombia and El Salvador to the list of countries with confirmed cases. The other nations are Austria, Canada, Costa Rica, Denmark, France, Germany, China (Hong Kong), Ireland, Israel, Italy, Mexico, the Netherlands, New Zealand, South Korea, Spain, Switzerland, the U.K., and the U.S.
Canadian health officials on May 2 reported the world’s first known case of swine flu jumping to pigs from a human, probably after a farm worker in the province of Alberta became ill during a trip to Mexico. Hundreds of pigs on the farm showed symptoms of the same H1N1 strain in humans and were recovering, according to the Canadian Food Inspection Agency.
Infected Swine
Pigs are an ideal breeding ground for new forms of the flu, and further genetic scrambling can result in deadlier forms of the new swine flu, said Nancy Cox, chief of the flu division at the Center for the Immunization and Respiratory Disease at the Atlanta-based CDC.
The animals serve as a “wonderful mixing vessel” for bird, human and swine viruses, Cox said. The process of two viruses merging to form a new virus, called reassortment, can also take place in humans.
New viruses formed through reassortment can have different properties than either of the two “parental viruses,” she said, sometimes producing deadlier diseases and complicating vaccine production.
The three main seasonal flu strains -- H3N2, another form of H1N1, and type-B -- cause 250,000 to 500,000 deaths a year globally, according to the WHO. The new flu’s symptoms are similar: aches, coughing, and fever. The CDC says people with the swine flu are more likely to have diarrhea.
No Immunity
Even if swine-flu symptoms are mild, the ease with which the new virus can spread among a world population with no natural immunity makes it a threat, health officials said.
Data so far suggest the virus is striking younger patients than is typical for influenza, and younger patients than usual are entering hospitals, Schuchat said. “Very few” patients with swine flu are older than 50, and the median age is 17. It’s possible that the elderly have greater immunity.
The WHO raised its six-tier alert to 5 on April 29 and a further elevation would signal a pandemic, alerting governments to carry out plans to curb the disease.
“I would still propose that a pandemic is imminent,” said Michael Ryan, the agency’s director of global alert and response, at a news conference May 2.
WHO Alert
International health experts said the world is now closer to another influenza pandemic than at any time since 1968, when the last of the previous century’s three pandemics occurred. The WHO hasn’t had a phase 6 alert since it introduced the six-level system in 2005. Before last week, the warning had been at phase 3 since 2007, when it was elevated for an outbreak of avian influenza, according to the WHO Web site.
The new flu strain has now struck more people than the H5N1 avian influenza that emerged in 2003. That illness killed more than half of the 421 who contracted the malady worldwide. Unlike swine flu, it didn’t spread from person to person.
The Spanish flu of 1918, another version of bird flu, killed as many as 50 million people in one of history’s deadliest outbreaks.
“We’re not seeing the factors that were associated with the 1918 pandemic, we’re not seeing the factors that were associated with other H1N1 viruses, and that’s encouraging,” the CDC’s Besser said. Because the virus is new and possibly evolving, “I don’t think it’s time to let our guard down.”
Flu Shots
The U.S. is hastening production of its annual flu shots based on strains identified before the H1N1 outbreak, said Kathleen Sebelius, who was confirmed as the U.S. Health and Human Services secretary last week. That will make capacity available if vaccines are needed for swine flu, she said.
“We are ramping up and accelerating the production of seasonal flu vaccine to make sure that we kind of clear the decks,” she said on “This Week,” an ABC News program, yesterday. “Ultimately the scientists will tell us whether or not production of that vaccine makes sense.”
Batches of seed virus are being developed for potential vaccine production, according to the WHO. Sanofi-Aventis SA of Paris, Baxter International Inc. of Deerfield, Illinois, and GlaxoSmithKline Plc of London, are talking with world health authorities about producing shots, the agency said.
Authorities advised hand-washing, hygiene and staying home if sick as the most effective ways to control the outbreak. The WHO and CDC said closing borders or killing animals are costly steps that wouldn’t slow the spread of flu.
Prevention in humans
- Prevention of pig to human transmission
The transmission from swine to human is believed to occur mainly in swine farms where farmers are in close contact with live pigs. Although strains of swine influenza are usually not able to infect humans this may occasionally happen, so farmers and veterinarians are encouraged to use a face mask when dealing with infected animals. The use of vaccines on swine to prevent their infection is a major method of limiting swine to human transmission. Risk factors that may contribute to swine-to-human transmission include smoking and not wearing gloves when working with sick animals.
