In addition to cholera and typhoid, officials are concerned about other bacterial and parasitic infections, such as salmonella, E. coli, cryptosporidiosis, or strongyloidiasis, to name a few, said Roger Lewis, Ph.D., an associate professor and director of the Environmental Health Laboratory at Saint Louis University School of Public Health in Missouri.

"A lot of these microorganisms that would be flushed into the ocean or rivers are now sitting in a stagnant pool," Dr. Lewis said in an interview. The lack of sanitation in New Orleans and other flooded communities poses a major health risk. "All this fecal matter can really produce an incredible amount of pathogenic microorganisms."

Even fecal matter from the dead can pose a health risk. Typically, a decomposing body does not pose a health risk. However, Dr. Lewis said, there could be a potential threat if the dead cannot be located and collected quickly and if the decomposing body had a virulent infection at the time of death. Rescue workers who come into contact with the dead, Dr. Lewis said, and are unaware of any infection, could be susceptible.

Even if the death toll "remains in the low hundreds, the waterborne illnesses are significant," Dr. Lewis said.

The CDC and FDA advise flood victims who do not have access to bottled water to boil and bleach tap water, but Dr. Lewis said these older recommendations are not practical for the current situation.

"How are you going to boil it because there's no power and where are people going to get chlorine right now?" he said.

Mosquito-borne illnesses, including West Nile, malaria, dengue, and even yellow fever, are concerns now given the extensive amount of still water throughout the hot and humid Gulf Coast where temperatures are in the 90s, Dr. Lewis said. How quickly officials can get some of this water drained, he added, could help minimize the risk of potential mosquito-borne illness outbreaks.