At least five people were in U.S. hospitals with swine flu as the number of cases nationwide rose to 68 on Tuesday and a federal health official warned that deaths were likely.
Most of the nation's confirmed cases were in New York City, where the health commissioner said "many hundreds" of schoolchildren were ill with what was "most likely swine flu." The city announced 45 confirmed cases, all affiliated with a Catholic high school.
Los Angeles County public health officer Dr. Jonathan Fielding said Tuesday during a news briefing that news reports of two possible deaths there were initially "misreported."
The Los Angeles County coroner's office ruled out swine flu as the cause of one those deaths. Coroner's Assistant Chief Ed Winter said Tuesday that swine flu was not found in a La Mirada man. Winter says lab testing is pending in the case of a 33-year-old Long Beach man but swine flu is now not suspected.
However, one top official from the U.S. Centers for Disease Control said going forward, flu deaths are likely. After all, some 36,000 people die each year from seasonal influenza, according to the CDC.
"I fully expect we will see deaths from this infection," said Richard Besser, acting director of the CDC.
That was echoed by Homeland Security Secretary Janet Napolitano.
"It is very likely that we will see more serious presentations of illness and some deaths as we go through this flu cycle," she said.
Of the 11 confirmed swine flu cases in California, none are in Los Angeles County, Fielding said.
“We have not yet identified a case in L.A., but we’ve increased our surveillance activities in the past week and we believe we will find and confirm flu cases in our county,” he said.
“We currently are investigating two possible flu clusters in two schools," he continued. "And since swine flu can only be confirmed by lab testing, it takes several days for a case to be confirmed. We have at this point two probable cases and two possible cases of swine flu.”
Elsewhere, there are six confirmed cases in Texas, two in Kansas and one each in Indiana and Ohio. New Jersey and North Carolina have suspected cases.
South Carolina changed the status of two suspected cases to two "probable cases" of swine flu after laboratory results were returned.
"Of the viruses sampled, two were type A, unsubtypable. That means, because this is a novel virus, we will assume that these two cases that were tested at the lab do have the new swine flu virus and these will now be considered 'probable cases,' so they are being sent to the federal Centers for Disease Control and Prevention for further evaluation and testing," said Dr. Jerry Gibson, chief of DHEC's Bureau of Disease Control.
Internationally, Cuba suspended flights to and from Mexico, becoming the first country to impose a travel ban to the epicenter of the epidemic. Argentina suspended flights from Mexico, as well.
The mayor of the capital of Mexico cracked down further on public life, closing gyms and swimming pools and ordering restaurants to limit service to takeout.
Confirmed cases were reported for the first time as far away as New Zealand and Israel, joining the United States, Canada, Britain and Spain.
Swine flu is believed to have killed at least 159 people in Mexico.
In Mexico City, authorities opened the national naval hospital to civilians to deal with the still-mounting wave of suspected swine flu cases, and prospective patients crowded the waiting rooms and reception areas for a chance to get in.
Complaints were heard throughout the capital of 20 million that the supply of surgical masks was running out.
The economic toll also spread. Officials said Mexico City is losing $57 million a day amid a shutdown that includes schools, state-run theaters and other public places. The government said it was closing all of Mexico's famed archaeological sites until further notice.
Treating/Preventing Swine Flu
Besser said Monday people can best protect themselves against the swine flu threat by taking precautions they were taught as kids, like frequently washing their hands and covering their mouths when coughing.
He said there is no reason for Americans to begin wearing face masks as residents of some Mexican states are now doing.
There is no vaccine available to prevent the new swine flu. However, there are antiflu drugs that do work once someone is sick.
Scientists hope to have a key ingredient for a vaccine ready in early May, but it still will take a few months before any shots are available for the first required safety testing. Using samples of the flu taken from people who fell ill in Mexico and the U.S., scientists are engineering a strain that could trigger the immune system without causing illness.
"We're about a third of the way" to that goal, said Dr. Ruben Donis of the CDC.
But if a vaccine eventually is ordered, the CDC already has taken a key preliminary step — creating what's called seed stock of the virus that manufacturers would use.
In the meantime, the virus appears responsive to the antiviral drugs, like Tamiflu and Relenza, which can be used to reduce the severity of the flu if used within two days of the appearance of symptoms.
Dr. Robert A. Salata, chief of the Division of Infectious Disease at University Hospitals Case Medical Center in Cleveland, told FOXNews.com that the fact that the severity of the virus can be weakened by antiviral drugs is encouraging.
"This past flu season, all of the influenza type A viruses like this one, were resistant to Tamiflu," said Salata, who is also a professor at Case Western Reserve University. "These viruses appear to be sensitive to all four antiviral drugs on the market."
Roughly 12 million doses of Tamiflu will be moved from a federal stockpile to places where states can quickly get their share if they decide they need it, Homeland Security Secretary Janet Napolitano said.
Salata said people should be cautious, but not panic.
New York Worst Hit State
In New York, there were growing signs that the virus was moving beyond St. Francis Preparatory school, where sick students started lining up last week at the nurse's office. The outbreak came just days after a group of students returned from spring break in Cancun.
At the 2,700-student school, the largest Roman Catholic high school in the nation, "many hundreds of students were ill with symptoms that are most likely swine flu," said Health Commissioner Thomas Frieden. The cases haven't been confirmed.
Twelve teachers reported flu-like symptoms as well, said the principal, Brother Leonard Conway.
A nearby public school for special education students was shut down after more than 80 students called in sick. Frieden said that some of the students have siblings at St. Francis.
"It is here and it is spreading," Frieden said.
Meanwhile, President Barack Obama asked Congress for $1.5 billion in emergency funds to fight the illness.
The U.S. stepped up checks of people entering the country and warned Americans to avoid nonessential travel to Mexico. Canada, Israel and France issued similar travel advisories.
For all the government intervention, health officials suggested that efforts to contain the flu strain might prove ineffective. Around the world, officials hoped the outbreak would not turn into a full-fledged pandemic, an epidemic that spreads across a wide geographical area.
"Border controls do not work. Travel restrictions do not work," said WHO spokesman Gregory Hartl, recalling the SARS epidemic earlier in the decade that killed 774 people, mostly in Asia, and slowed the global economy.
The pork industry was dealing with a public relations nightmare over the virus, which is a never-before-seen hybrid of human, swine and bird influenza that is widely called swine flu.
Public health officials have said people cannot get sick from eating pork, but some countries, such as China, Russia and Ukraine, have banned imports from Mexico and parts of the U.S.
The Associated Press, Reuters and FOXNews.com's Marrecca Fiore contributed to this report.