The New York State Health Department has set up a 24-hour, toll-free hotline to answer questions about the illness. The number is 1-800-808-1987.
The school, which will remain closed again Wednesday, is where the first cases were reported last week after a class trip to Mexico. It is the greatest cluster of the illness in the United States.
Frieden says the flu, which has killed more than 150 in Mexico, is relatively mild in the city and is spreading no differently than the typical flu.
Additionally, Mayor Michael Bloomberg said there are five new probable cases. One of those cases is related to St. Francis.
Two cases are unrelated to the St. Francis community.
Among those is a two-year-old Bronx boy who has been hospitalized. A woman who was hospitalized in Brooklyn is also suspected of having swine flu. Both are now recovering.
Another cluster of the disease is suspected at P.S. 177 on 188th Street, located not far from St. Francis Prep.
According to Bloomberg, 82 students have called in sick, 11 with documented high fever, from the special needs school. One student at the school has two siblings at St. Francis.
The mayor said he would not be surprised if they all tested positive, but it should not matter because none of the cases are severe.
Three adults, including the school's assistant principal, were also sent home. The assistant principal tested negative for swine flu.
"Many of our children don't speak [because they are autistic]," said the school's United Federation of Teachers representative Shernice Blackman. "So if they're not feeling well, teachers are always watching them for cues of lethargy. It makes it a little bit more difficult.... Our nurse was on rollerskates yesterday."
Students were sent home with a letter saying the school would be closed on Wednesday.
The mayor and health commissioner say Ascension School in Manhattan is also being investigated as a swine flu cluster.
During a news conference Tuesday, Governor David Paterson and state health officials said they are working to contain the virus and that all cases so far have been mild with quick recovery times.
They stressed people should go about their daily lives.
"I would just like to assure all New Yorkers that we are taking every step we can possibly imagine to contain this virus and to keep our public safety foremost in mind," the governor said. "This is not a time for alarm. But it is a time to be alert."
Anyone with possible symptoms is urged to contact medical professionals and restrict contact with others.
Richard Besser, the acting director for the Centers for Disease Control, says as with any widespread virus, deaths are to be expected.
Meanwhile, Cuba has suspended flights to and from Mexico for 48 hours. It's the first country to impose a travel ban as the swine flu virus reaches overseas.
The move comes after global health officials say voluntary travel restrictions were ineffective.
Canada, Israel and France are also warning against nonessential travel to Mexico.
Global health officials say the virus appears to be establishing itself in communities outside Mexico and could produce larger outbreaks.
In response to the outbreak, Mexico City has closed gyms, swimming pools and told restaurants to limit service to take out only. The country has already shut down a wave of schools and public places.
The number of suspected deaths in Mexico is now more than 150.
A second case of the virus has also been confirmed in Spain, as 26 others remain under close watch.
In Israel, two cases have been confirmed, both from men who recently returned from Mexico.
New Zealand has confirmed three cases in a group of 11 people who reported symptoms after recently returned from Mexico.
The World Health Organization is maintaining its threat level, which is two steps below a full-blown pandemic.
The phase-four alert means there is sustained human-to-human transmission and containment is no longer possible.
The U.S. State Department and the Centers for Disease Control and Prevention has put out a warning against traveling to Mexico.
Homeland Security Secretary Janet Napolitano said Tuesday that the Obama administration would not wait for a WHO declaration of a pandemic to deliver a pandemic-like response.
President Barack Obama told a gathering of scientists in Washington Monday that the situation is a cause for concern, but not alarm.
However, the number of cases is growing nationwide. New Jersey and Michigan are now reporting suspected cases of swine flu.
There are dozens of cases of swine flu in the United States in five states: New York, Ohio, Kansas, Texas and California.
Only one person in the U.S. who contracted the flu has been hospitalized.