In a widely anticipated emergency meeting today in response to the swine flu threat, the World Health Organization announced that it is raising its pandemic alert level to Phase 4 from Phase 3-- the first time the alert level has been raised above 3 since the system was adopted in 2005.
The Phase 4 designation signifies that the new swine flu virus can cause sustained outbreaks and is adapting itself to spread among humans -- significant steps toward a pandemic. But the ranking does not necessarily mean that a pandemic is a foregone conclusion.
To slow the spread of the virus, the State Department issued a travel alert this evening, recommending that Americans avoid any non-essential travel to Mexico. In addition, the Food and Drug Administration has authorized public health and medical officials to use influenza medications, like Relenza and Tamiflu to treat the virus and deal with the emergency situation.
Meanwhile, 20 additional cases of swine flu have been confirmed at a New York City school, boosting the total number of cases there to 28, New York City Mayor Michael Bloomberg said today.
Bloomberg warned that there are another 17 possible cases, all in people associated with the school, St. Francis Preparatory School in Queens, and as many as 100 of the students have fallen ill and will be tested for the virus.
Some of the school's students had recently returned from a spring break trip to Mexico.
The mayor expressed optimism, however, over the fact that the disease has not yet been detected anywhere else in the city.
"We are still dealing with a single cluster of swine flu cases, all associated with this one school," Bloomberg said, adding that to his knowledge all of those infected with the virus were improving.
"So far, we are not seeing a situation comparable to that being reported in Mexico."
The total number of swine flu cases throughout the U.S. rose to 50 today, The Associated Press reports. The challenge confronting public health officials around the world is how to stop a disease from spreading when it travels by human contact.
Today the Centers for Disease Control and Prevention announced a new travel advisory for Americans visiting Mexico, according to Dr. Richard Besser, acting director of the federal agency.
Besser made the announcement this afternoon at a press conference.
While swine flu cases in the United States appear to be less severe than those in Mexico, and no deaths have yet been reported, U.S. health officials warned that the outbreaks could get worse, asking Americans to avoid any non-essential travel to Mexico.
"What I want people to understand is that we're concerned," Besser told "Good Morning America" today. "People should be concerned. We'll tell you what we know when we know it."
The United States has not reported any swine flu fatalities, Besser said Americans need to be prepared for it to get worse.
"I think from what we understand in Mexico, people need to be ready that we can see more severe cases in this country," he said.
Addressing the National Academy of Sciences on Monday, President Barack Obama acknowledged the efforts to keep pace with the spread of the disease within the United States.