The first two known human cases of infection with the strain of swine flu that is suspected to have caused the death of up to 159 people in Mexico were in the U.S. in late March, according to a report from the U.S. Centers for Disease Control and Prevention.

The infections were in two children who later recovered.

According to the CDC's Morbidity and Mortality Weekly Report, "CDC determined that two cases of febrile respiratory illness occurring in children who resided in adjacent counties in southern California were caused by infection with a swine influenza A (H1N1) virus ... that previously has not been reported among swine or human influenza viruses in the United States or elsewhere."

"The viruses from the two cases are closely related genetically, resistant to amantadine and rimantadine, and contain a unique combination of gene segments," said the report, which was reviewed by Dow Jones Newswires.

Neither of the two children - a 9-year-old girl from Imperial county with symptoms reported on March 28th and a 10-year-old boy from San Diego county with symptoms reported on March 30th - had contacts with pigs, the report said.

According to the CDC report, the identification of the new virus was made on April 17th.

After having identified the two cases as the new swine flu strain, the CDC sent an advance copy of the report on the findings to the Mexican health authorities in the evening of April 20th, Mexican Health Ministry Spokesman Miguel Angel Lezana told Dow Jones Newswires.

While no fatalities had been confirmed from the virus at the time the CDC identified the virus, Mexican health authorities were investigating the death of 20 influenza patients.

Following the CDC alert, Mexico sent 53 samples from the influenza patients to the U.S. for testing, of which 17 were confirmed to have tested positive for the new mutation, which is a mix of swine, avian and human influenza, Lezana said.

After Mexico received this confirmation at 3 p.m. local time on April 23rd local authorities held emergency meetings, which led to Health Jose Angel Minister Cordova announcing a local health emergency on national television later that evening, Lezana said.

Mexico has since closed down virtually every public space in the capital, suspended all cultural activities from theater to cinemas, and shut schools nationwide until May 6th in a move to contain the spread of the virus.

The influenza outbreak has taken on international dimensions, with the World Health Organization warning of the possibility that it may develop into a global pandemic. Mexico's Health Minister Jose Angel Cordova said Tuesday evening that there have been seven confirmed deaths from the virus in Mexico, with 159 suspected deaths due to the virus.

 
   15 Of First Confirmed Cases From Mexico City

Lezana said that of the samples Mexico sent to the U.S., one had come from a woman in southern Oaxaca state who later died, 30 from Veracruz on the Gulf Coast and 22 from the Mexican capital area.

The 17 cases which tested positive to the new virus included 15 cases from Mexico City, the case from Oaxaca - which on April 13th was recorded as the first death from the virus - and one of a 4-year-old boy from a small Veracruz town near Perote, a coffee producing region.

The case of the boy in the town near Perote was initially identified as an influenza A strain known as H2N3, but was eventually confirmed as a case of the new A/H1N1 strain, Lezano said.

He said that in preliminary investigations involving the identification of a new virus it is not unusual that test results can switch between different strains and multiple tests some time have to be done to confirm the presence of the new virus, as in the boy from Veracruz.

Residents in Perote complained to local authorities after about a third of the population came down with the flu, which they blamed on a local pig farm operated by Smithfield Foods Inc. (SFD), local media reported. The company has denied the presence of swine flu on its facilities.

Mexican Health Minister Cordova earlier this week said the cases of influenza in Veracruz didn't cause the government to raise an alarm because there was no sign of the emergence of a new strain of swine flu since the people affected were given standard flu treatment and there were no fatalities.

Lezana heads the Health Ministry's National Center for Epidemiologic Vigilance, or Cenavece.

 
   -By Maja Wallengren, Dow Jones Newswires; 5255-5080-3452; maja.wallengren@dowjones.com