Health Authorities Study Swine Flu's Differences in Severity
Wednesday, April 29, 2009
Health authorities raced yesterday to unravel the many mysteries about the ominous new swine flu spreading around the world, including how widely the virus might cause the severe form of illness that so far has been restricted to the epicenter of the outbreak in Mexico.
As the number of confirmed infections in the United States jumped again and cases were confirmed for the first time in Britain, New Zealand and Israel, researchers searched for clues as to how readily the virus causes the pneumonia that has hospitalized and killed patients in Mexico. Only a handful of patients in the United States and elsewhere outside Mexico have been hospitalized, severe complications have been relatively rare, and no one has died.
"We still do not have a good explanation for why the pattern of cases in other countries appear relatively mild while the pattern of cases in Mexico appear to be much more severe," said Keiji Fukuda of the World Health Organization. "This will be the object of a great deal of research and attention, but at this time, we can't say why there appears to be a difference."
Experts said there are several possibilities: Victims in Mexico may be more vulnerable because of nutritional deficiencies, other infections or some other factor; medical care may be better in the United States and elsewhere; the virus could be weakening as it spreads; or too few cases may have occurred outside Mexico for severe illnesses to emerge.
"This is the mystery," said Arnold Monto, an influenza expert at the University of Michigan. "You could speculate about so many things. It's an incredibly important question."
Several officials said some deaths outside Mexico are probably inevitable.
"I fully expect we will see deaths from this infection," Richard E. Besser, acting director of the Centers for Disease Control and Prevention in Atlanta. "They're seeing many deaths in Mexico, and we're trying to learn more about that and why the situation in Mexico is different from here. And as we continue to investigate cases here, I expect that we will see deaths in this country."
Among the most severe U.S. cases has been an adult in California's Imperial County who ended up on a ventilator, said county health officer Stephen W. Munday.
Several experts said they think the most likely reason for the milder illnesses outside Mexico was that there have been too few cases reported elsewhere to see the full spectrum of disease the virus is causing.
"The most obvious explanation is there have been many more cases in Mexico," said Frederick G. Hayden, a University of Virginia influenza expert. "So what we're seeing is the small number of people developing complications, some of whom have gone on to have to fatal outcomes."
If that is the case, the number of hospitalizations would increase and deaths would probably occur as the virus spreads, even if the proportion of patients who become severely ill is relatively small. During the devastating 1918 Spanish flu pandemic, about 2 percent of patients died, meaning 98 percent recovered.
"We could be at that same level and in that ballpark," Hayden said. "We just don't know."
Another possibility is that patients in Mexico experiencing the most severe illness have been infected with something else, as well, perhaps a bacterium.
"We've known for decades that influenza is notorious for increasing the risk of secondary bacterial complications," Hayden said.
Also, many of the Mexican victims may have delayed treatment.
"Probably, very valuable time was lost," said Julio Frenk, the dean of the Harvard School of Public Health who was Mexico's health minister between 2000 and 2006. It is also likely that many Mexicans are more poorly nourished than Americans and "more susceptible to infection," he said.
Although so far genetic analyses of the viruses in Mexico and elsewhere appear identical, scientists will be studying samples as the virus passes from one person to another for any sign that it might be becoming less threatening.
"If you get viruses along the way and can look at those, that can give you a sense as to whether, as it moves from person to person, it's changing, becoming less severe, more severe or no change at all, and that is all very important information," Besser said.
WHO's Fukuda said it is possible that even if the virus spreads widely, it could produce a "mild" pandemic, but he cautioned that the 1918 pandemic had a mild first wave and then returned to cause millions of deaths.
President Obama, meanwhile, asked Congress yesterday for an additional $1.5 billion to fight the swine flu. The money could be used to produce more antiviral drugs, work on developing a vaccine or fight the spread of the disease, White House press secretary Robert Gibbs said.
The request came as the number of U.S. cases climbed from 48 to at least 64, with at least 45 in New York, one in Ohio, two in Kansas, six in Texas and 10 in California. Only five U.S. patients have been hospitalized.
New York officials said there are signs that the outbreak continues to spread. Mayor Michael R. Bloomberg (I) said there are probably hundreds of cases at St. Francis Preparatory School, where the outbreak began, and new cases were suspected at a Queens public school for autistic children and a Catholic school in Manhattan, along with scattered cases in Brooklyn and the Bronx.
In addition to the U.S. and Mexican cases, at least six have been confirmed in Israel, at least two in Spain, two in Britain and two in New Zealand, according to WHO. Israeli officials said they had confirmed two more cases, both in men who recently returned from Mexico.
Although WHO recommended against travel restrictions, Cuba and Argentina banned travel from Mexico. Several countries, including France, Britain, the Netherlands and Italy, advised residents to avoid unnecessary trips to Mexico.
In India, officials were searching for 500 British tourists to check them for swine flu and said they would increase the number of health surveillance booths at nine international airports to screen travelers.
Chinese officials reported no confirmed cases on the mainland, but state media reported that a Hong Kong woman who developed flulike symptoms after a trip to the United States was being tested.
Correspondents Jill Drew in Beijing, Edward Cody in Paris, Howard Schneider in Jerusalem and Emily Wax in Mumbai and staff writers Keith B. Richburg in New York, Spencer S. Hsu and Michael D. Shear in Washington, Ceci Connolly in Atlanta, and Ashley Surdin and Karl Vick in Los Angeles contributed to this report.