Katrina pounded Louisiana, Mississippi and Alabama, causing extensive flooding, widespread devastation and leaving millions without electricity.
The federal government began rushing meals, medical teams, baby formula, communications equipment, generators, water and ice into hard-hit areas, along with doctors, nurses and first-aid supplies.
Some areas could be without power for weeks, local energy officials say. Ten major hospitals in New Orleans were running on emergency backup power.
Michael Brown, the director of the Federal Emergency Management Agency said Tuesday that additional medical personnel were being moved in to treat evacuated hospital patients.
With at least one New Orleans hospital threatened by Katrina’s floodwaters, patients were being transferred to the Superdome, he said.
Not safe for residents to return home
Government officials were urging the public not to return to their homes yet, but to hold off until first responders and emergency workers could clear the hardest hit areas and city streets.
In some of the low-lying areas most heavily hit by flooding, it could be weeks before residents can return to their neighborhoods, Brown told NBC's "Today" show Tuesday.
The Department of Health and Human Services sent 38 doctors and nurses to Jackson, Miss., to be used where needed, and 30 pallets of medical supplies to the region, including first aid materials, sterile gloves and oxygen tanks.
In the coming days, Gulf Coast residents will be confronting significant health risks from contaminated water and food supplies. When people finally get back home, they will be dealing with a lack of clean drinking water and spoiled food from the loss of electricity.
"The needs don’t end when the storm recedes," says Dr. Jeffrey Goldhagen, director of the Duval County Health Department in Florida.
For example, a 50-foot water main broke in New Orleans, making it unsafe to drink the city’s water without first boiling it.
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"There are concerns about the well supply, sanitation, safety of the drinking water and food supply and waste disposal," says Patrick Libbey, executive director of the National Association of County and City Health Officials in Washington.
Infections and heat-related illnesses
People are also vulnerable to heat-related illnesses and dehydration, conditions which can be compounded by the lack of clean drinking water.
Immediate infections that could result from exposure to filthy floodwaters include gastrointestinal illnesses, diarrhea, salmonella, hepatitis viruses and skin infections from infected wounds.
"It's the perfect setup for skin infections," says Dr. Jeff Starke, head of infectious diseases control at Texas Children's Hospital in Houston.
There could also be some unexpected encounters with poisonous or dangerous wild animals disoriented by the hurricane and flooding. New Orleans mayor Ray Nagin told MSNBC TV Monday that he had "serious concerns" about poisonous snakes or alligators wandering into the city.
"People need to stay conscious that they can run into a snake or alligators that usually live in the swamps," he said.
Mosquitoes are another danger in flooded areas, so during clean-up it's recommended to use insect repellents that contain DEET or Picaridin and to wear long-sleeved clothing especially during early morning and evening hours. Mosquito bites can cause infectious illnesses such as West Nile.
Contaminated water and food
Although simply coming in contact with floodwaters doesn't pose a serious health problem, health officials recommend that people sterilize anything that comes in contact with floodwater. Children should not be allowed to play in floodwaters.
The Centers for Disease Control and Prevention offers some safety rules for drinking water, cooking and personal cleanliness:
- Do not use contaminated water to wash dishes, brush teeth, wash and prepare food, wash hands, make ice, or make baby formula. If possible, use baby formula that does not need to have water added.
- If clean water is not available, use an alcohol-based hand sanitizer to wash hands.
- Use only bottled, boiled, or treated water. Boiling water for one minute will kill most organisms. If using bottled water, make sure it is uncontaminated. Water should be treated or boiled before use.
- If boiling is not possible, water can be treated with chlorine or iodine tablets or unscented household bleach. If using household chlorine bleach, add 1/8 teaspoon of bleach per gallon of water if the water is clear. For cloudy water, add 1/4 teaspoon of bleach per gallon. Mix the solution thoroughly and let it stand for about 30 minutes before using it. However, treating water with chlorine or iodine tablets or bleach will not kill parasitic organisms and should only be used to clean items.
- Pregnant women and infants younger than six months should not drink boiled water. Boiling may concentrate potentially harmful nitrates in the water.
Any food that has come in contact with contaminated floodwater should not be eaten. Undamaged canned food can be used, if the labels are discarded and the cans are thoroughly washed and disinfected in the bleach solution before opening.
Food will keep cool in a refrigerator without power for about four hours if the door is unopened. Thawed food can be eaten if it is still cold, but if there is any doubt, it's best to throw it out. Any food that has been at room temperature for more than two hours or has an unusual odor should be discarded.
As recovery begins, residents will be coping with emotional stress as well as the physical dangers of clean-up. Post-traumatic stress can last for weeks or months and it's best to seek medical care when feeling anxious or sick, experts say. Children and the elderly are particularly vulnerable.
The Associated Press contributed to this article