The US government has declared a public health emergency following Hurricane Katrina.
But just how likely is it that diseases will take a hold?
West Nile Virus cases could rise because of the hurricane
Fears about disease epidemics following natural disasters are nothing new.
Just days after the Boxing Day tsunami some were claiming the death toll from disease could be larger than from the wave itself.
As it turned out there were no epidemics, despite isolated outbreaks of measles, dengue fever and malaria.
Once again the threat has been raised following the hurricane in the US.
Michael Leavitt, secretary of health and human services, said a public health emergency was in place from Louisiana to Florida.
He warned there were grave concerns about cholera, typhoid and dehydrating diseases, while others said West Nile Virus could be a problem.
But health experts are predicting the impact will be somewhat more limited.
Outbreaks of diseases such as cholera and typhoid are not likely because the microbes which carry them are virtually non-existent in the US.
Instead, the biggest risk is expected to come from contaminated water, which as well as being harmful to health, provides an ideal breeding ground for mosquitoes.
The Centres for Disease Control and Prevention, part of the US government's health department, and the Food and Drug Administration is advising people to throw away food that may have come into contact with flood water and only to drink bottled water.
CDC records from previous US disasters, including Hurricane Floyd which hit North Carolina in 1999, show the majority of medical problems after the events have been associated with diarrhoea and asthma.
Dr Glenn Morris, a professor of epidemiology at the University of Maryland Medical School in Baltimore, said: "The biggest problem is the sewage contamination of the water.
"Just splashing around in the water, if there is sewage contamination there is a risk you could get it on to your hands and get it into your mouth."
He said viruses such as hepatitis A could be a threat as well as dangerous strains of E.coli.
But he said dead bodies, unless they were carrying specific bacteria and viruses, were unlikely to contaminate the water with disease.
Others remain confident further disaster will be averted.
Dr Jean Luc Poncelet, director of the Pan American Health Organization's disaster preparedness team in the US, added: "If you look at the natural disasters that have happened over recent years, disease outbreaks have been kept to a minimum.
"Even diseases following the tsunami in south east Asia were kept largely under control.
"Many of the diseases we do see in developing countries such as cholera are not an issue in the US.
And Dr Poncelet added: "The emergency response in a country like the US is likely to stop any outbreaks as long as people following basic hygiene guidelines and don't drink or bathe in the flood water.
"Contaminated water can be found everywhere the world over, if you know the dangers you can prevent the problems."
However, one virus which may cause a problem is West Nile Virus, a potentially deadly condition which peaks in the US in August and September. Last year it killed over 200 people in the US.
Professor Ivor Van Heerden, a public health specialist from Louisiana State University, said he expected to see more cases as the flood waters could lead to an explosion in mosquito numbers.
"We expect there will be a very dramatic increase in the mosquito population and possibly a few weeks from now we'll start seeing a greater number of people brought in with Nile fever."
He also warned there could be more cases of rabies as the flood waters would have disrupted wild animals from their normal habitats.