Dr. Miguel Angel Lezana told The Associated Press late Thursday his center alerted the Pan American Health Organization on April 16 about alarming occurrences of flu and atypical pneumonia in Mexico. But no action was taken until eight days later when the World Health Organization said it was "very, very concerned" the outbreak could grow into a pandemic.
"It seems it should have been more immediate," Lezana, director of the National Epidemiology Center, told AP in a telephone interview.
Across the country's border, the number of confirmed swine flu cases in the United States rose to near 150 Thursday. Hundreds of schools nationwide shut their doors.
But the Centers for Disease Control and Prevention said the current flu strainas the deadly 1918 virus.
The only confirmed U.S. swine flu death so far was a Mexican toddler who succumbed in Texas. New cases were confirmed Thursday in Europe, but no deaths had been reported outside North America.
In Mexico, the outbreak's epicenter, new cases and the death rate were leveling off, the country's top medical officer said. Health authorities said they have confirmed 300 swine flu cases and 12 deaths due to the virus.
"The fact that we have a stabilization in the daily numbers, even a drop, makes us optimistic," Mexican Health Secretary Jose Angel Cordova said. "Because what we'd expect is geometric or exponential growth. And that hasn't been the situation."
But as Mexico shut down non-essential government and private business Friday to begin a five-day break aimed at further slowing the spread of the virus, the country's epidemiology chief faulted WHO and its regional branch, PAHO, for not stepping in earlier.
Lezana said that after a rash of flu and pneumonia cases emerged in Mexico in April, his department was so alarmed that it notified by e-mail the local office of PAHO, as called for by international protocols.
"The procedure is very clearly established," Lezana said. "You have to notify the local office, then it sends the notification to the regional office. They analyze the data and decide whether to send it to the WHO in Geneva."
Lezana said the illnesses raised a red flag because the flu was occurring at least a month after flu season normally ends in Mexico.
But four days later, PAHO still had not responded, so the National Epidemiology Center again contacted the local PAHO office and asked for an explanation and whether more information was needed, Lezana said.
PAHO responded that the alert was being handled, he said. But Lezana said that as far as he knew, the PAHO regional office in Washington and WHO took no action until April 24, when WHO announced an epidemic was under way.
Lezana had learned just the day before, from a testing of a sample that Mexico sent to a lab in Canada, that people were coming down with a new, mutated and lethal swine flu virus. By then, more than 1,000 people had been sickened in Mexico.
Lezana told AP that to prevent delays in the future, there should be an investigation of the WHO's handling of the crisis, adding that the public health agency should decide whether it should be an internal or an independent probe.
WHO has not commented publicly on the alleged delay. But PAHO spokesman Daniel Epstein confirmed to The Washington Post that the agency got a message from Mexican authorities on April 16 about an unusual disease outbreak.
Epstein, who is with PAHO's Washington office, told the newspaper that it was impossible for authorities in Geneva not to have learned of it at the same time, describing a system that sends messages through to WHO headquarters automatically.
There is a perception that Mexico was slow to react to the outbreak, and Lezana denied it.
"We didn't wait. We notified them in time of this event," he said, adding that while Mexico waited for WHO to assist, it tried to stem the outbreak and identify it.
Mexican medical teams did do some detective work that epidemiologists recommend for tracking a killer bug, including interviewing 472 people who may have come into contact with the first known swine flu fatality, Adela Maria Gutierrez, a 39-year-old from Oaxaca. Samples were taken from her and sent to the lab in Canada.
But only 18 people - all hospital workers - of the 472 people were tested for swine flu. In other parts of Mexico, the follow-up appears to have been weak. Health workers only started visiting the families of victims this week to see if they also contracted the illness.
France, Switzerland and the Netherlands became the latest countries to report infections.
France's health minister said the patients, a 49-year-old man and a 24-year-old woman, both recently returned from Mexico. Roselyne Bachelot said Friday both are "doing well." They are hospitalized in Paris.
Bachelot also said another patient "very probably" had the virus, though it has not yet been confirmed.
Canada, New Zealand, Britain, Germany, Spain, Israel and Austria also have confirmed cases.
The Red Cross said it was readying an army of 60 million volunteers who could be deployed around the world to help slow the virus' spread.
The impact was most evident in Mexico City. Traffic cleared in the notoriously clogged avenues, and the attorney general's office said crime was down one-third compared with last week. Mexico City's infamous smog dropped to levels normally seen only on holidays.
Mexican President Felipe Calderon said authorities would use the extensive shutdown beginning Friday to consider whether to extend emergency measures or ease some restrictions. The five days include Friday's Labor Day holiday, the weekend, and the Cinco de Mayo observance on Monday, minimizing the disruption.
2009 H1N1 Flu Outbreak Map:
This is a map depicting confirmed and suspected cases of the 2009 H1N1 outbreak, with contributors from all over the world, from a variety of backgrounds including health, journalism, technology.