Yesterday Mayor Bloomberg confirmed that swine flu has hit New York, and the federal government declared a national public health emergency. The current outbreak is believed to have originated in Mexico, where the virus is suspected to have caused 81 deaths and 374 hospitalizations as of yesterday. The eight confirmed cases in New York are all from St. Francis Prep in Fresh Meadows, where some students recently returned from spring break in Mexico.

Though only eight cases were confirmed, a whopping 100 students at St. Francis have exhibited swine flu symptoms, which include upset stomach, fever, lethargy, lack of appetite, coughing, runny nose, sore throat, nausea, vomiting and diarrhea. A team from the health department got stuck in traffic en route to the school Friday, and by the time they arrived most of the students had gone home for the weekend. So they were only able to test nine students out of 75, and it's likely that the number of confirmed cases will rise. The school is closed today and tomorrow while a cleaning company sanitizes the building.

The H1N1 strain of swine influenza is usually associated with pigs, but when it spreads person to person—instead of from animals to humans—it can continue to mutate, making it difficult to fight off. The health department is now on "high alert," and officials will be checking every 12 hours to determine if any of the roughly 60,000 patients admitted to emergency rooms in an average day had flu symptoms. But yesterday Bloomberg encouraged people with flu symptoms to avoid hospitals unless they were seriously ill, so as not to infect others. He also urged everyone not to panic: "Just go about your business, enjoy the good weather."

Feeling reassured? The CDC has more on their web page"Swine Flu and You." And a very interesting article in the LA Times examines pandemics past and wonders what they tell us about how this one might unfold. Not much, apparently; one molecular virologist says, "It's impossible to say with any assurance what's going to happen. Influenza viruses can evolve quite quickly." Dr. Scott Layne, an epidemiologist at the UCLA School of Public Health, explains that inspecting the virus itself is of little help until scientists figure out how it spreads: "The microscope doesn't tell you anything. What are the genetic correlates of virulence? Unknown. Transmissibility? Unknown."