Senior citizens need to prepare for the possibility of going it alone in the first few hours or days of a disaster, the U.S. Centers for Disease Control and Prevention said on Thursday.

The call for action by seniors at an aging conference in Chicago is aimed at avoiding the horrific consequences of Hurricane Katrina, including the death of more than two dozen residents of a Louisiana nursing home.

Despite public awareness efforts, about half of all Americans are still not prepared for the inevitable next disaster, the CDC said. The agency is trying to drive the message home that vulnerable seniors need to take some individual responsibility for preparation.

"In the initial stages of a disaster, especially a powerful hurricane or other wide-scale event, people are typically on their own, at least for a while," the CDC statement on seniors and disaster preparation reads.

This is most dangerous for the elderly and disabled, who "should assume they might not be able to reach their doctors or pharmacies, receive home-delivered meals or obtain their usual home health services" in the aftermath of a disaster, it adds.

Katrina slammed into the U.S. Gulf coast in August 2005, stranding thousands of people and killing nearly 1,300. About 70 percent of the victims of Katrina were older than 60, according to the AARP, formerly the American Association of Retired Persons, the seniors' advocacy group.

The elderly and seriously ill in New Orleans, the city most devastated by Katrina, were among the last to escape the flooding that came when the city's protective levees broke.

"Individuals have a responsibility. When nothing big has happened for a while, people get complacent," said Alison Johnson, a CDC disaster planning official.

The loss of life after Katrina was a "wake-up call about all of our vulnerable populations, and how we have to do a better job" to prepare them, she added.

For seniors able to prepare on their own, or with the help of family, the CDC recommends they have on hand a basic emergency supply kit; a list of what they should bring with them if they have to flee, including medications, hearing aids, extra batteries and oxygen; and a list of doctor and pharmacy phones numbers in a waterproof bag.

Fran Brooks, an emergency disaster official with the Florida Department of Elder Affairs, said food packs distributed by government agencies following disasters, intended for soldiers and emergency personnel, have too many calories and too much sugar for seniors. Brooks said they could send the elderly into glucose shock or a high-blood pressure crisis.

Nursing homes face an especially tricky problem, particularly with transportation. Local officials in Louisiana said bus companies do not want to sign up to be on call for emergencies, because of liability issues.

In a report last year, the inspector general for the U.S. Health and Human Services department said those residents in nursing homes who stayed in place fared better than those who attempted to escape.