Officials estimate it will be weeks before New Orleans' water supply is restored and probably about as long for electricity to return.

Officials also warned against a variety of imminent problems, including the need to minister to the mental health needs of survivors who have lost nearly all their possessions.

The biggest problem they face is that modern medicine requires large amounts of electricity and there was very little available on Tuesday -- and for the foreseeable future.

At least 10 hospitals in New Orleans were using generator-supplied electricity, and several have already closed. State health authorities have been transporting critically ill patients out of New Orleans by boat, helicopter and bus, said Dr. Jimmy Guidry, the state health officer.

About 2,500 patients were not initially evacuated from the city because they were so ill that moving them might kill them, and must now be moved. Some 500 high-risk patients -- some breathing with ventilators -- must also be evacuated from the city.

Back-Up Generators Failed

Tulane University Medical Center said Tuesday that its emergency generator was in danger of being drowned by the still-rising floodwaters, and all of its remaining patients were transferred to the Superdome, which is already housing at least 10,000 tourists and newly homeless.

Four people -- three of them hospital patients -- died on Monday night at the Superdome, Guidry said.

"Right now our concern is with the living," he said. "We know people are fragile. We're doing everything we can, but we're going to lose some people."

Charity Hospital and Baptist Hospital in the heart of New Orleans were both heavily damaged and have been closed, perhaps permanently. The New Orleans Times-Picayune reported that medical workers at Charity Hospital had to manually ventilate patients after back-up generators failed.

Beyond the immediate problems are a host of impending problems, said Dr. Jeffrey Goldhagen, director of the Duval County Health Department in Florida and a veteran of hurricane planning.

In a city of 500,000, like New Orleans, there are probably 5,000 who require kidney dialysis twice a week, he said.

"Where will they get it? Where will two-month-olds get their immunizations?

Where will people get their pharmaceuticals for the next three to six months?"

Contaminated Water Could Spread Diseases

Doctors at the University of Alabama Medical Center in Birmingham were warned late Tuesday to expect infants from neonatal intensive care units in Jefferson Parish that had been shut down by the flooding.

The principal water main supplying New Orleans broke during the storm and reservoirs have been contaminated by overflowing sea water and sewage.

Officials estimate it will be weeks before the water supply is restored and probably about as long for electricity to return.

Some officials are worried that the contaminated water could spread diseases, such as cholera, dysentery and other gastrointestinal infections.

Fears of such outbreaks in the wake of flooding are always present, but officials said such fears are generally overblown. As long as fresh water is provided, such outbreaks are very unlikely, Guidry said.

Federal troops and National Guardsman are already trucking in bottled water, ice, and food -- especially the infamous military MREs, or meals ready to eat -- and are prepared to continue the process for as long as necessary.

The Centers for Disease Control and Prevention on Tuesday sent five truckloads of medical supplies to Louisiana, including cots, blankets, pharmaceuticals, towels, surgical masks and other equipment. The agency has also sent in 38 physicians to help out, said spokesman Tom Skinner.