Senior citizens planning to tour Alaska or the Yukon in the next month should check with their doctors.

Nearly 2,000 people have been sickened and two 79-year-old travelers have died from a flu outbreak that's hit Alaska and the Yukon Territory in Canada during their peak tourist season.The federal Centers for Disease Control and Prevention on Thursday urged tourists who are older than 65 or have respiratory problems to consult their doctors before traveling to the affected area by cruise ship, train or bus.

"We're clearly not saying stay home," said Dr. Marty Cetron, a CDC epidemiologist. "By and large, what we're saying is be aware that the risk is out there."

From May through September, up to 70,000 travelers tour Alaska and the Yukon every week. Passengers riding in close quarters can easily spread the flu.

Researchers believe the outbreak stems from the influenza A virus, which commonly is a problem in the winter. The virus could have been lingering since last winter or brought up from a tourist in the southern hemisphere, where it's winter, Cetron said.

Flu vaccine isn't readily available during the summer, but doctors can prescribe medicine that can blunt the effects of the flu virus, Cetron said.