Outbreak in Mexico May Be Smaller Than Feared

Workers at the Naval Hospital in Mexico City wore protective gear Friday in the area where people with possible flu symptoms were checking in.

By DENISE GRADY and LIZ ROBBINS

Published: May 1, 2009

The swine flu outbreak in Mexico may be considerably smaller than originally feared, test results released there on Friday indicate.

Of 908 suspected cases that were tested, only 397 people turned out to have the virus, officially known as influenza A(H1N1), Mexican health officials reported at a news conference. Of those, 16 people have died.

Mexico had reported about 2,500 suspected cases as of Friday, but the number of real cases could turn out to be less than half the suspected number if further testing follows the same pattern as the original round. Officials said that the tests were being done quickly, and that 500 more would be completed Friday.

José Ángel Córdova, Mexico’s health minister, said, “This is a new epidemic, and we can’t predict exactly” what it will do. “We need more days to see how it behaves,” he said.

“Apparently the rate of infection is not as widespread as we might have thought,” he added. The materials needed for the test were provided to Mexico by the United States Centers for Disease Control and Prevention.

Officials at the centers declined to say what the new numbers might mean.

“We are continuously assessing new information, but it is still too early to draw conclusions about the extent of the spread of this new virus in Mexico or the severity of disease caused by it,” Dr. Nancy Cox, chief of the influenza section, said by e-mail, when asked to comment on the test results.

Dr. Javier Torres, the head of the infectious disease research unit at the Mexican Social Security Institute, Mexico’s main public health care system, said that he had been analyzing the past week’s influenza statistics.

“The number of those exposed and infected has gone up, and the number of fatal cases has gone down,” he said. “We can be comfortable with those facts.”

Officials at the World Health Organization, which has declared that a pandemic is imminent, declined to comment beyond saying that the investigation into the outbreak was continuing.

But a public health and infectious disease expert from Vanderbilt University, Dr. William Schaffner, said the test results were “going to change, I think in a substantial way, the image of this outbreak in Mexico.”

If the outbreak is much smaller than initially thought, Dr. Schaffner said, “It would, I think, enable the world’s public health community to take a deep breath and continue to track the outbreak and reduce the tendency, as the W.H.O. has been doing, to notch up on its pandemic scale.”

If the testing also shows that the disease has caused fewer deaths than the 170 or so suspected, Dr. Schaffner said, it might resolve a question that has been puzzling health experts since the outbreak began: why did the disease appear to be so much more severe in Mexico than in the United States? In the United States, cases have been mild and there has been only one death, that of a 23-month-old child from Mexico. Meanwhile, the disease continued to spread to other countries and was confirmed in more American states on Friday. The disease is expected to drop off during the summer, because flu viruses do not thrive in heat and humidity, but it could rebound in the fall and winter. The World Health Organization said that the flu vaccine given to millions of people for the most recent flu season appeared ineffective against the A(H1N1) strain, but that health officials were talking to manufacturers about creating a new swine-flu vaccine, which would take four to six months to produce.

Dr. Marie-Paule Kieny, director of the Initiative for Vaccine Research at the World Health Organization, said that unless the numbers of cases decreased significantly, “it seems mostly likely that the manufacturers will proceed and we will certainly support them.”

Officials at the Centers for Disease Control said a decision had not yet been made about whether to manufacture a vaccine, but President Obama said that the government would support it.

New cases were reported in Denmark, France, Russia, Hong Kong and South Korea on Friday, but they were not confirmed by the health organization. The United States reported 141 confirmed cases in 19 states, up from 109 cases in 11 states on Thursday.

Concerns about the disease are having an increasing impact. On Friday, a United Airlines flight with 245 passengers heading from Munich to Dulles Airport in Washington landed in Boston instead because a female passenger had flu symptoms and the airline thought she needed prompt attention, a United Airlines spokesman said.

In New York, the school with the nation’s largest cluster of swine flu to date — St. Francis Preparatory School in Fresh Meadows, Queens — was set to reopen Monday after being closed for a week.

Researchers say that some genetic features of the virus may help explain why many cases tend to be mild.

“We do not see the markers for virulence that were seen in the 1918 virus,” said Dr. Cox, of the Centers for Disease Control. “However, we know there is a great deal we don’t understand about the virulence of 1918 or other viruses that have a more severe clinical picture in humans.”

It is too early to know what economic impact, if any, the flu outbreak might have on the United States economy. The Congressional Budget Office estimates that the recession will push this year’s national economic output 7.5 percent below its potential level. A true flu pandemic could shave off an additional 1 to 4.25 percent and could have a similar effect on the world’s output, too, some economists say.