TUESDAY, April 28, 2009 (HealthDay News) -- The number of confirmed cases of swine flu in the United States continued to climb Tuesday, to 64, with all the bulk of the new cases coming from the New York City high school that had previously reported 18 cases of the infectious disease, U.S. health officials said.
"There are 64 confirmed cases in the United States in five states," Dr. Richard Besser, acting director of the U.S. Centers for Disease Control and Prevention, said during an afternoon teleconference. "Forty-five in New York, one in Ohio, two in Kansas, six in Texas and 10 in California.
Although cases in the United States continue to be mild, more severe cases are expected, Besser said, adding, "as we move forward, I fully expect we will see deaths."
California authorities were investigating whether two recent deaths were linked to the outbreak, according to published reports.
Besser said three people have been hospitalized in California and two in Texas. The incubation period for the U.S. cases is two to seven days, which, he said, "is typical for what you see with an influenza virus."
The majority of new cases in New York continued to come at St. Francis Preparatory School in Queens. Some students who have come down with the infection had been to Mexico during a spring break to Cancun, the Associated Press reported.
As with the previously tested strains of the never-before-seen swine flu virus, new testing found that the pathogen remains susceptible to the two common antiviral drugs Tamiflu and Relenza, according to an April 28 dispatch from the CDC's Morbidity and Mortality Weekly Report.
The new flu strain is a combination of pig, bird and human viruses, prompting worries from health officials that humans may have no natural immunity to the virus.
Meanwhile, the AP reported Tuesday that the epidemic had crossed new borders, with the first cases confirmed in the Middle East and the Asia-Pacific region. And the number of deaths in Mexico -- thought to be the source of the outbreak that continues to reach around the world -- surpassed 150. Mexico is the only country to report deaths caused by the new swine flu strain of flu. Cases in all other countries have been described as mild.
On Tuesday, Cuba suspended flights to and from Mexico, becoming the first country to impose a travel ban, even though the World Health Organization said such bans were ineffective, because the virus has already taken root in at least six countries, the AP said.
Despite the reports out of Mexico, there was a glimmer of good news. The number of new swine flu cases reported by Mexico's largest government hospitals has been declining the past three days, government officials said, from 141 on Saturday to 119 on Sunday and 110 Monday, the AP reported.
Still, on Monday, U.S. officials said they were tightening their travel advisory to Mexico, recommending that all nonessential travel to that country be avoided.
And late Monday, the World Health Organization raised the alert level over swine flu from 3 to 4, two levels shy of declaring a pandemic. A level 4 alert means there is sustained human-to-human transmission of the virus causing outbreaks in at least one country.
Mexico on Tuesday was reporting as many as 1,900 possible swine flu infections and as many as 152 deaths.
Earlier Monday, President Barack Obama said the threat posed by the swine flu outbreak was a cause for concern but "not a cause for alarm."
The United States has stepped up checks of people entering the country by air, land and sea, looking for signs of infection, and the CDC plans to distribute "yellow cards at ports of entry," Besser said Monday.
"These will provide information on swine flu, so that people coming into the United States will have information about this outbreak -- what to do if they become sick, what things they can do to prevent the likelihood that they will become sick," he said.
He also said U.S. officials were questioning border visitors about their health, looking for signs of possible infection.
In Mexico, authorities continued to take dramatic steps to try to contain the outbreak. Government officials have canceled all school until May 6, and the Mexico City government is considering a complete shutdown, including all public transportation. And the Cinco de Mayo parade celebrating Mexico's defeat of a French army on May 5, 1862 and Mexico City's traditional May 1 parade have been canceled, the AP said.
For more on swine flu, visit the U.S. Centers for Disease Control and Prevention.