MEXICO CITY — Mexican officials, scrambling to control a swine flu outbreak that has killed at least 16 people and possibly dozens more in recent weeks, shuttered schools from kindergarten to university for millions of young people in and around the capital on Friday and urged people with flu symptoms to stay home from work.
“We’re dealing with a new flu virus that constitutes a respiratory epidemic that so far is controllable,” Health Minister Jose Angel Cordova told reporters late Thursday, after huddling with President Felipe Calderón and other top officials. He said the virus had mutated from pigs and had at some point been transmitted to humans.
Mexico’s flu season is usually over by now, but health officials have noticed a significant spike in flu cases. The World Health Organization reported about 800 cases of flu-like symptoms in Mexico in recent weeks, most of them among healthy young adults, with 57 deaths in Mexico City and 3 in central Mexico.
That is a worrisome pattern because seasonal flus typically cause most of their deaths among infants and old people, while pandemic flus — like the 1918 Spanish flu, and the 1957 and 1968 pandemics — often strike young, healthy people the hardest.
Doctors believe that is because young adults have more vigorous immune systems — which mount an assault on the new virus known as a “cytokine storm” — that may actually overwhelm the victim’s own lungs by causing inflammation and drawing in fluid.
It was clear that Mexican health officials were alarmed. Besides shutting classes, the government urged people to avoid large gatherings and to refrain from the common greetings of a hand shake or kiss on the cheek. City buses continued to operate but some passengers were seen wearing masks, and a cough or a sneeze by one passenger prompted others to relocate.
Health officials in the United States were working to determine whether the Mexican outbreak was tied to the unusual strain of swine flu that has been circulating among people in the American Southwest but is not known to have caused any deaths, according to the Centers for Disease Control and Prevention.
The agency, which has found only seven cases in the United States, expects to find more now that it has begun looking intensively for them.
“We don’t yet know the extent of the problem,” said Dr. Anne Schuchat, the director of respiratory diseases for the agency, “but we don’t think this is a time for major concern.”
Five of the people infected were in Imperial and San Diego Counties in California and two were in San Antonio. They were 9 to 54 years old. None had any contact with pigs, and in two sets of cases — involving a father and daughter and two 16-year-old schoolmates — those infected had contact with each other. That convinced the authorities that the virus was being transmitted from person to person.
The seven people were apparently infected from late March to mid-April. Only one was hospitalized, and all recovered.
The A (H1N1) flu strain they had was quite unusual, said Dr. Nancy Cox, the chief of the agency’s flu division. It contained gene segments from North American swine, bird and human flu strains as well as one from Eurasian swine.
Like some human strains, it is resistant to two older flu drugs, amantadine and rimantadine. It is not resistant to Tamiflu or Relenza. However, Tamiflu resistance is common in the H1N1 human flu strain circulating this year, so the swine strain could become resistant to Tamiflu if the viruses mixed in humans or, possibly, in pigs.
Swine flus rarely infect humans. There have been about a dozen cases since 2005, but almost all were in farm workers or others in contact with pigs.
In 1976, there was a cluster of swine flu cases among soldiers at Fort Dix, in New Jersey, one of whom died. That led to a rush to make a new vaccine and administer it to 40 million Americans. No epidemic materialized, but thousands of people claimed that the vaccine had given them Guillain-Barré syndrome, which can cause lethargy or paralysis. The episode led to the resignation of the director of the disease control center, and the agency has been wary of causing panic over influenza cases ever since.
The unusual strain this year was noticed, Dr. Schuchat said, only because the agency was trying out a new diagnostic test at a Navy laboratory and doing more testing than usual through a new Border Infectious Disease Surveillance Project along the Mexican border.
Officials at the public health agency in Canada said their Mexican counterparts had warned them this week of a “relatively high” fatality rate for people in Mexico who have had respiratory illnesses this season, some of whom had tested positive for flu.
The United States flu season is tailing off now. It has been relatively mild; the major surprise had been the widespread Tamiflu resistance in the circulating human H1N1 strain. (Resistance is close to 100%!)
Dr. Cox of the disease control center said officials did not yet know whether the flu shot this year protected against the new swine strain.
Source: The New York Times