BROOKLYN - Health officials say there are now 50 confirmed cases of swine flu in the United States.The cases include 28 students at a preparatory school in Queens. Officials say there are 17 other probable cases and that this is currently the only cluster of swine flu cases in New York City. 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 WHO 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, jointaches, severe headache and, in some cases, vomiting and diarrhea.AP wire services contributed to this reportWorldHealth Organization