Cramped living quarters on college campuses increase students' chances of being infected with all kinds of flu, but scrupulous hand hygiene and simple face masks may help some stay healthy, at least until swine fluvaccines become available next month, health experts say.

Last week, U.S. colleges and universities reported a 21 percent increase in new cases of influenza-like illness, or 6,432 cases, at 253 schools tracked by the American College Health Association.

So far this academic year, there have been 13,434 reported cases of flu-like illness, most of which are presumed to be swine flu because seasonal flu has not gotten under way. Many schools have just begun classes.

At the University of Michigan, researchers are tallying results from a two-year study on how best to protect students from flu-like illness.

In the first year of the study, the team found wearing face masks and using alcohol-based hand sanitizer helped cut the risk of flu by as much as 50 percent.

There was a significant reduction in influenza-like illness, Allison Aiello, an assistant professor of epidemiology, said in a telephone interview.

Aiello said in the first year of their study, the flu season was light, but results of the second year, expected to be published in the next few months, would give a better picture of how masks and hand sanitizer worked against lab-confirmed cases of flu.

With college students, the concern is that students are living in the residence halls, which can be quite crowded, Aiello said.

They sleep there. They eat there. They study there. If there is an outbreak of influenza, it can be quite concentrated and go through the population quite quickly, she added.

Being sprayed with droplets from someone's cough poses the biggest infection threat from the flu, accounting for more than half of all cases, followed closely by touching a contaminated object, which accounts for about a third, according to a study published this week in the journal Risk Analysis.

Aiello said there were things campuses could do to reduce the risk of infection, including asking students to practice the non-pharmaceutical interventions until swine flu vaccines are ready in mid- to late October.

When the vaccinations are available, we recommend students get seasonal flu vaccine, but also the novel H1N1 vaccine, she said.

Manufacturers and governments have been scrambling for vaccines to target the new H1N1 flu strain, which was declared a pandemic in June. The World Health Organization said it could infect as many as one-third of the world's population, or 2 billion people.