MEXICO CITY – The schools and museums are closed. Sold-out games between Mexico’s most popular soccer teams are being played in empty stadiums. Health workers are ordering sickly passengers off subways and buses. And while bars and nightclubs filled up as usual, even some teenagers were dancing with surgical masks on.

Across this overcrowded capital of 20 million people, Mexicans are reacting with fatalism and confusion, anger and mounting fear at the idea that their city may be ground zero for a global epidemic of a new kind of flu — a strange mix of human, pig and bird viruses that has epidemiologists deeply concerned.

Tests show 20 people in Mexico have died of the new swine flu strain, and that 48 other deaths were probably due to the same strain. The caseload of those sickened has grown to 1,004 nationwide, Mexico’s Health Secretary Jose Angel Cordova said.

The same virus also sickened at least eight people in Texas and California, though there have been no deaths north of the border, puzzling experts at the U.S. Centers for Disease Control and Prevention.

Dallas County officials said Friday that any patient with upper respiratory ailments should be tested for swine flu. The warning comes after a strain of swine flu was diagnosed in five people in California and two in Texas.

None of the seven people that have been diagnosed had been in contact with pigs, which is how people usually catch swine flu, and all recovered from the illness.

The Texas cases are 16-year-old boys who are friends and live in Guadalupe County, near San Antonio. Also, one of the California cases — a 10-year-old boy — traveled to Dallas this month.

Swine flu symptoms are mostly involving fever, cough and sore throat, though some of the seven also had vomiting and diarrhea.

Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza that regularly cause outbreaks of influenza among pigs. Swine flu viruses do not normally infect humans, however, human infections with swine flu do occur, and cases of human-to-human spread of swine flu viruses has been documented.

History

1918 epidemic
Between the autumn of 1918 and the spring of 1919, 548,452 people died of this flu in the US. In the UK, France and Germany, around 600,000 people died. Worldwide, the number of casualties was between 20 and 50 million, or maybe more.

1976 U.S. outbreak
There is “enough evidence to suggest that” about 500 cases of Guillain-Barré syndrome resulting in death from severe pulmonary complications for 25 people was caused by an immunopathological reaction to the vaccine in some people.

2007 Philippine outbreak
The mortality rate is less than 10 % for swine flu, if there are no complications like hog cholera.

2009 Mexico and U.S. outbreak
In March and April 2009, over 1,000 cases of unusually virulent flu in humans were detected in Mexico and the southwestern United States, causing more than 60 deaths.