It is likely to be weeks before the health consequences of Hurricane Katrina are known. But recent experience with similar natural disasters in the United States suggests that most deaths will have occurred when people trapped in automobiles drowned, that many survivors have minor injuries, and that large-scale outbreaks of disease will not occur.

In particular, epidemics of cholera and typhoid sometimes seen in the developing world when drinking water becomes contaminated are impossible because the microbes are not present in the population.

Standing water, even when heavily polluted, is not very dangerous in itself, provided people do not drink it and routine medical care of wounds is available. Dampness, however, may lead to some increase in skin rashes and asthma attacks, if the experience of recent floods holds in this one.

Every hurricane has its own personality. Katrina's extreme size and force, combined with the unusual topography of some of the places it struck, may ultimately produce unusual health consequences. But experts were not willing to sketch an out-of-the-ordinary profile for Katrina yesterday.

"We don't have any accurate statistics now in terms of what has gone on," said Tom Sinks, acting director of the National Center for Environmental Health, at the Centers for Disease Control and Prevention.

"In these circumstances, it usually takes us a certain amount of time to get a needs assessment. You have to have people out in the field collecting information. It can't occur when the storm is hitting and people are hunkered down," he said.

It was virtually impossible to get firsthand information yesterday on Katrina's health consequences to date. Officials at the Louisiana Department of Health and Hospitals could not be reached by telephone or e-mail, but the Associated Press reported that federal officials said 2,500 patients in New Orleans were being evacuated because at least seven hospitals in Orleans Parish were threatened by the loss of their power generators and other problems. Of scores of patients moved to the Superdome, city authorities said four had died.

Forty-three of Mississippi's 82 county health departments were closed "to relocate personnel to areas of greatest need," said a state health department statement. The state has 400 public health nurses and 130 food-and-water inspectors, and many have been sent to Mississippi's devastated Gulf Coast counties, a spokeswoman said.

One obvious need was for medical care for people in shelters. The American Red Cross was helping care for 41,000 people in 254 shelters, including 96 in Mississippi and 88 in Louisiana. By midday yesterday, nurses in about 25 shelters had reported people with chronic illnesses who needed prescription drugs, said Dee Yeater, an expert in disaster health services in the Red Cross's national headquarters in Washington.

The CDC official warned that asphyxiation deaths from gas-powered generators is a particular worry now. "I can tell you that after every one of these we will see carbon monoxide poisonings, and they are 100 percent preventable," Sinks said.

The experience of North Carolina during and after Hurricane Floyd in 1999 gives a rough picture of storm and flood effects.

Of the 52 deaths directly attributable to the hurricane, 36 were drownings, and 24 of those involved occupants of motor vehicles trapped in floodwater. Seven people died in car crashes, four people of heart attacks, and others of burns, electrocution or falls.

In the week after the storm and flood, people in Floyd's path suffered an increase in suicide attempts, dog bites, fevers, skin problems, and shortages of medicines and services such as dialysis and vaccination. A month later, they reported higher-than-usual rates of insect bites, diarrhea, asthma and violent injury, according to the CDC's Morbidity and Mortality Weekly Report.

After extensive flooding in Missouri in 1993, there were no acute outbreaks of disease. Over a six-week period, hospital emergency rooms reported 542 flood-related medical conditions. Of that total, 48 percent were injuries, and 45 percent were illnesses. Skin rashes, diarrhea and heat-related problems were the most common illnesses, according to another CDC report.

After being rescued from his New Orleans home yesterday by boat, Brian Gayton cries for his grandmother, whom he lost in the hurricane. Levee breaks have added to the city's woes.