As college students begin leaving for summer vacation, the H1N1 virus, also known as swine flu, is cropping up on a surprising number of campuses across the nation. Some national experts say this trend could be an ominous sign for students and health centers in the fall, when flu season traditionally intensifies.

"If we continue to see outbreaks of H1N1 during the summer, we should prepare for having a lot of influenza in the fall, and that's going to put significant pressure on health services on campuses across the country to respond," said Anita L. Barkin, director of student health services for Carnegie Mellon University, who led a panel about the flu at the American College Health Association's annual meeting in late May. "Even though H1N1 ... is not as virulent or severe as the virus of 1918, when you have a lot of sick people on your campus, it tends to disrupt the day-to-day functioning of campus business."

The earlier "outbreak" of H1N1 began in late April. Some colleges suspended classes and events as a precaution, even though actual cases were few and generally mild. As of May 30, there have been more than 13,000 cases and 27 deaths confirmed by the Centers for Disease Control and Prevention in the United States.

But in recent days, numerous colleges and universities have reported new cases. Last week, Princeton University announced that three graduate students and one adult graduate dependent had tested positive for the swine flu. As of that time, they were fully recovered or recovering. At Stanford, at least nine potential cases developed from mid-May to early June. Virtually all are on their way to recovery, according to a spokeswoman, Lisa Lapin.

Other cases around the country include:

• The University of Scranton, in Pennsylvania, reported one confirmed case and two potential cases last Friday. All have been treated and the students are recovering.
• Five students at Ner Israel Rabbinical College, in Baltimore, Md., were confirmed to have swine flu, though none were hospitalized and all recovered within two days.
• One student at Tompkins Cortland Community College, part of the State University of New York system, tested positive while taking summer school classes. He was moved out of his apartment and into isolation, where multiple offices within the college worked to provide for him until he recovered.
• When one student at Pennsylvania's Kutztown University was diagnosed with swine flu during summer sessions at the end of May, the student's class was told and the classroom was disinfected.
• At Lawrence University, in Wisconsin, at least two cases have been confirmed. Other students may have contracted the flu, but recovered before they could be confirmed.

Barkin called the number of recent outbreaks "unusual." "Typically you don't see a lot of influenza in the summer because people are outside more often, not inside in confined spaces," she said.

Students planning to travel overseas this summer are especially susceptible to H1N1, and campus officials should keep an eye out when they return in the fall, Barkin said.

At the American University in Cairo, two American graduate students were diagnosed and hospitalized over the weekend, according to Mary Corrarino, vice president of the university. While they are recovering, their dormitory has been quarantined and classes are suspended for a week.

With these warnings on the horizon, few colleges have devised new concrete plans for the fall. Many institutions with confirmed cases have been sticking to pandemic response plans put into place before the swine flu outbreak.

"We've had a pandemic planning team in place for years in preparation for avian flu," said Matt Santos, director of university relations at Kutztown, noting that the plan devised to prevent that flu is similar to that for the swine flu. At Lawrence, where at least two cases have been confirmed and multiple other cases have been reported at surrounding colleges, information dissemination is very important, according to Nancy Truesdell, the dean of students and vice president for student affairs there. The pandemic plan involves stepping up communication among the health center, the larger campus and the surrounding community, in addition to isolating the flu victims and taking necessary medical precautions. Encouraging people who think they may have the flu to come forward to be tested is key to containing the disease, Truesdell said.

Barkin says that each case is just the "tip of the iceberg" when it comes to the total number of cases in the surrounding community. What's going around is a relatively mild form of influenza that people are recovering from quickly, which is good but not a solution, she said.

"What do we need to do this summer to prepare for a pandemic -- not only a pandemic like 1918, but a pandemic that looks like H1N1, only maybe a little bit worse," she said. That includes educating the public about hygienic habits like hand-washing and cough etiquette, as well as thinking ahead about how to manage residential communities and sick faculty.

"The longer (the flu) stays around, the more opportunity you have for it to become a more persistent, virulent type of virus that could cause more problems in the fall," Barkin said.