Classes resumed at the Rye School for Leadership Tuesday after the school was closed due to swine flu fears.

According to county health officials, a student at the school who traveled to Mexico became ill April 3. Officials say 18 other students and staff members got sick within the last two weeks.

School officials decided to close the school Monday so the building could be disinfected. Parents who spoke to News 12 Westchester say they feel safer knowing the school was disinfected, even though it?s not believed anyone had swine flu.

The county health commissioner says there is no evidence anyone at the school had swine flu and that "it may just be a coincidence." School officials say most of those who fell ill are doing much better, but there are about four students at the tail end of the illness with minor symptoms. Doctors are recommending they stay home for 24 hours.

There are currently 64 confirmed cases of swine flu in the United States, including 28 students at a preparatory school in Queens. Swine flu is suspected in up to 152 deaths in Mexico, with 20 deaths confirmed so far.

The virus, which began in Mexico, has spread to at least six other countries, and World Health Organization has raised its alert level to 4. That is two steps below pandemic stage. New Zealand has confirmed the virus in 11 people who recently returned from Mexico, and a man in Israel has also been confirmed with swine flu. Spain confirmed its second case Tuesday.

None of the cases outside Mexico have been fatal.

Symptoms of swine flu include a fever of more than 100, coughing, joint aches, severe headache and, in some cases, vomiting and diarrhea.

AP wire services contributed to this reportWorldHealth Organization