Floodwaters in New Orleans contain bacteria associated with sewage that are at least 10 times higher than acceptable safety levels, making direct contact by rescue workers and remaining residents dangerous, the first government tests confirmed Wednesday.

Five deaths in Texas and Mississippi have already been attributed to contact with the toxic water, the CDC reported Wednesday, as New Orleans Mayor C. Ray Nagin ordered forced evacuations of residents remaining in the city. Though a large scale outbreak of infectious disease has yet to materialize, the health risks posed by the polluted water remained a top health concern.

"Human contact with the flood water should be avoided as much as possible," said Environmental Protection Agency Administrator Stephen L. Johnson.

Also found in the first round of testing were elevated lead levels, a risk if people, particularly children, were to drink the water.

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Residents have been told since Hurricane Katrina to avoid drinking the water, but EPA's first tests -- which tracked levels of E. coli and other coliform bacteria that are a marker for sewage contamination -- emphasize a risk from skin contact as well. The bacteria can cause infections if people have cuts or other open wounds, or if the water is splashed into their mouths, noses or eyes.

The EPA didn't test how much sewage was in the water, but quit when analyses hit the 10-fold mark.

The first round of tests searched for more than 100 chemicals and other pollutants, but only coliform and lead so far exceeded EPA safety levels, the agency said.

But this was just a first test, of water in some residential neighborhoods, not industrial areas -- and didn't include tests for petroleum products because the of oil in the water is obvious, Johnson said.

"We don't know what else is contained in that water," he stressed, saying that daily samples from different parts of the city were being taken -- and that chemicals such as asbestos are likely to be in debris from older homes and businesses.

The health hazards from this water make it imperative that remaining residents comply with evacuation orders, said Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention.

"If you haven't left the city yet, you must do so," she said.

Symptoms of E. coli ingestion are vomiting, diarrhea, stomach pain and fever; anyone with those symptoms, or who has open wounds exposed to the dirty water, should seek medical attention.

Federal health officials stressed that rescue workers need to wear protective clothing and gloves before entering flooded areas, and that anyone who comes into contact with the dirty water should be careful not to splash it into their faces -- and to find clean water and soap to wash exposed skin, especially hands, as soon as possible.

"Always, always, always wash hands before eating," Gerberding stressed.

The five reported deaths appear to have been caused by Vibrio vulnificus, a germ common in warm Gulf Coast waters that's usually spread by eating contaminated food but that can penetrate open wounds, too. The four deaths reported Tuesday — one a hurricane refugee evacuated to Texas, the other three in Mississippi — were attributed to wound infections, said Tom Skinner, spokesman for the Centers for Disease Control and Prevention, which received the reports from officials in the two states.

On Tuesday, officials in Houston's Astrodome handed out alcohol-based hand sanitizers Tuesday to help prevent spread of norovirus, an easily spread cause of diarrhea and vomiting. Officials isolated some refugees with the illness, made infamous by recent cruise-ship outbreaks, although they couldn't provide an exact count. There is no treatment except to keep sufferers hydrated; it normally lasts a few days.

Infection control within shelters housing thousands of evacuees is a top priority, said Dr. Julie Gerberding, the CDC director.

Wounds infected by submersion in New Orleans floodwaters tainted with raw sewage and other bacteria are common, however. Gerberding said Tuesday that another concern is whether those waters also were contaminated with toxic chemicals from hurricane damage to nearby factories.

Drinking water safety also is an issue in much of Mississippi and Louisiana and parts of Alabama, and the EPA sent a mobile laboratory to Mississippi Tuesday to help assess that. More than 1,000 drinking water systems in the three states were affected by the hurricane.

Officials maintain that there is little disease risk from exposure to dead bodies in the flooding — the corpses aren't infectious — or from agents not typically seen in this country, such as cholera.

Instead, doctors are being urged to watch for more likely causes of diarrheal illnesses: E. coli bacteria; the easy-to-spread noroviruses that, while seldom life-threatening, can cause days of misery; or Vibrio vulnificus, cholera-like bacteria that every year kill more than a dozen Gulf Coast residents. The deaths reported Tuesday were among elderly people or those with weak immune systems, CDC's Skinner said.

But infection isn't the biggest medical challenge. It's how to care for thousands of people with chronic diseases like diabetes or kidney failure, many of them elderly patients who depend on numerous medications daily.

In Tupelo, Miss., for instance, city doctors brought sacks full of prescription drug samples to the Good Samaritan Clinic, where volunteer doctors are treating about 100 evacuees a day almost exclusively for chronic conditions, said Dr. J. Edward Hill, one of the volunteers and president of the American Medical Association.

FOX News medical contributor Dr. Manny Alvarez said that the destruction wrought by the storm would continue to pose a health threat long after the water was drained. The wetness left behind creates an environment for mold and bacteria to develop, he said.

The storm also destroyed the city's medical infrastructure, Alvarez warned, leaving residents without any facilities or resources that can provide them with health care.

"All of the health care structures in New Orleans and around New Orleans are devastated," he said. "A lot of these people got their clinical care at community health centers and mental health centers. All of that is gone."

Alvarez, who spent four days volunteering at a shelter in Baton Rouge, La., said that while the focus has been on treating acute patients, the larger crisis would be with people with chronic conditions who have not had their medications.

"This will be one of the greatest American health tragedies of the century," Alvarez said.

The Associated Press contributed to this report.