Life is returning to normal in Mexico after a five-day shutdown caused by the global swine flu outbreak.

Businesses and schools are reopening after a thorough scrubbing, but the annual Cinco de Mayo celebrations are canceled this year.

Meanwhile, U.S. officials believe it's too early to say the threat is over.

"We also have in mind that H1N1 flu could die down and then return in the fall when flu season is back in full swing," Homeland Security Secretary Janet Napolitano said.

Nearly 300 people in 36 states in the U.S. have been infected with the virus.

It has forced hundreds of school closings in Texas, New York and other states.

The Center for Disease Control and Prevention says the flu is likely to spread to every state.