LONDON: As schools around the world reopen, health authorities are bracing for a major spike in swine flu.

Schools are ideal breeding grounds for the virus. Not only are children more susceptible than adults to swine flu, but the crowded, sometimes unsanitary conditions give the virus a perfect chance to spread.

Countries on both sides of the Atlantic are closely monitoring schools, yet some have vastly different plans on whether they will close schools to fight the epidemic.

Both the U.S. and the United Kingdom say they will not close schools except under exceptional circumstances. U.S. Health and Human Services Secretary Kathleen Sebelius said a massive school closing wouldn't stop swine flu.

Experts say school closures simply buy time. They don't reduce the number of cases; they just spread them over a longer period. Closing schools is also disruptive and costly as working parents must juggle their schedules to take care of their children.

"With a mild virus like swine flu, I think it is not necessary to close schools," said Simon Cauchemez, a flu expert at London's Imperial College. "The only reason you would do it in the current outbreak is if you're afraid the health care system will be completely overwhelmed."

In France, however, officials may close schools if as few as three students have flu symptoms. The French education minister, Luc Chatel, recently outlined plans to shut schools for at least six days if three students in the same school catch swine flu. If many schools are closed, Chatel said France is ready to broadcast lessons on TV and radio.

Other European nations, including Austria, Germany, Spain and Switzerland, say they will consider closing schools on a case-by-case basis.

When swine flu first broke out in the spring, authorities in Mexico, the U.S., Japan, Germany, Britain and elsewhere closed schools for several weeks. Coupled with other measures such as intensified testing, flu treatment and the canceling of concerts, sports events and other mass gatherings, that seemed to slow the virus for a while.

But officials gave up shutting schools once swine flu became entrenched in communities.

Dr. Keiji Fukuda, the World Health Organization's flu chief, said the U.N. health agency did not have any blanket recommendations on closing schools. He said countries could consider closing schools in the fall, but noted that children aren't the only ones to spread swine flu.

"We're four months into this pandemic a lot of people in different age groups are able to spread infection," he said.

In previous flu pandemics, cases have surged almost as soon as schools reopened, but that also could be due to cooler weather, which makes it easier for flu viruses to spread, Fukuda said.

Still, if swine flu becomes more deadly, all bets may be off.

"If the disease becomes more severe, the balance might change," Cauchemez said. "The huge economic and social costs of closure might not seem so bad if the virus causes more deaths later."

For some parents, the inconvenience of school closures is worth the chance to spare their kids swine flu.

"More schools should take the necessary precautions to stop the spread of swine flu," said Kassidy Choi Schagrin, whose son attends Eton, an elite British private school that closed for about a week in the spring after several students caught the virus.

"I was rather grateful that the school closed instead of exposing healthy children and causing an epidemic," Schagrin said. "When it concerns a child, it is always better to be safe than sorry."

Students walk the campus of Texas Christian University in Fort Worth, Texas, on Tuesday, Aug. 25, 2009. Multiple confirmed cases of swine flu have been reported at the private university.