The question of who contracts and ultimately dies from this virus has become a matter of central concern in Mexico. And the answers that are beginning to emerge as the death toll rises have been ominous. Relatively young adults, presumably among the population's most healthy, have been the first to succumb. All 86 people suspected to have died of swine flu in Mexico were ages 25 to 50, said an official at the Health Ministry, speaking on the condition of anonymity.
All the 15 people in Mexico City who died from the virus were 25 to 37 years old, Ebrard said in a radio interview Sunday.
The high proportion of young adults among the fatalities is one of several mysteries about this virus. The same pattern emerged during the 1918-1919 Spanish influenza epidemic, which killed at least 50 million people, and it remains unexplained in that case as well.
One theory is that the virus triggers an excessively aggressive immune response that destroys the throat and lung tissue. Young adults, with the most robust immune systems, may be especially at risk.
Most of the fatal cases involved extensive lung damage, requiring doctors to prescribe mechanical breathing assistance. Exactly what caused the lung damage is not known.
Justino Regalado Pineda, an epidemiologist with the Health Ministry, said adults would be more likely to contract the flu simply because they tend to congregate more in public places, such as at their workplaces.
He speculated that one reason people have died in Mexico as opposed to the United States is that the life span of the virus could have been longer in Mexico.
After flu infections, people can develop an additional bacterial "superinfection" that could be lethal, said Brian Currie, an infectious-diseases doctor and vice president and director of clinical research at Montefiore Medical Center in New York City. Currie said it remained a mystery why people in Mexico were dying while the cases reported in the United States have been relatively benign.
"You've got to remember, this is a strain of flu nobody has seen before," Currie said.
Even though there is no known vaccine for humans for this strain of swine flu -- which combines genetic material from more common types of pig, bird and human flus -- Mexican officials have stressed that it is curable. President Felipe Calderón said Sunday that of the 1,324 patients with flulike symptoms as of Saturday, 929 have been treated and released from the hospital.
"Everybody's inside, places are closed, the parks are closed, people don't go out," she said. "Mexico is a social place -- people like to go out and be together. The sickness has taken that away."
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