CHICAGO (Reuters) - Catastrophic flooding from Hurricane Harvey increases the risk of ills ranging from skin rashes to bacterial and viral infections and mosquito-borne disease, U.S. public health officials warned on Monday.

Residents wait to be rescued from the flood waters of Tropical Storm Harvey in Beaumont Place, Houston, Texas, U.S., on August 28, 2017. REUTERS/Jonathan Bachman

The most immediate health risk is from drowning, especially for people trapped in vehicles, said Renee Funk, associate director for emergency management of the Centers for Disease Control and Prevention.

Carbon monoxide poisoning from portable generators is another threat. “Unfortunately, we expect there will be people who die from that and people will be poisoned from it,” Funk said in a telephone interview.

But simply wading in floodwaters could cause skin rashes because so much of the water is contaminated with toxic chemicals that get washed out of people’s garages and tool sheds.

“The No. 1 thing we’re concerned with in a flood is chemicals,” said Funk, who advises people to shower and wash their hands immediately after contact with floodwaters.

Mosquito-borne disease is less of an immediate threat because the floodwaters will wash out most mosquito breeding sites for disease-causing mosquitoes such Aedes aegypti, which spread Zika, chikungunya, dengue and yellow fever, she said.

Floods typically cause a rise in nuisance mosquitoes, such as the Culex variety, and these, too, can carry disease.

A year after Hurricane Katrina in 2005, regions in Louisiana and Mississippi affected by the flood reported a doubling of cases of neuroinvasive West Nile virus - cases in which the virus caused severe inflammation in the brain or spinal cord, said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.

“A year from now, we’ll have to look very closely at West Nile and other mosquito-borne viruses,” said Hotez, who is riding out the storm from his Houston home while his lab at Baylor is closed.

In the immediate aftermath of Harvey, bacterial diseases are a concern, although cholera, a scourge in the wake of many natural disasters in developing countries, is likely not a worry in Houston, he said.

“Bacterial infections are really important, such as salmonella and E. coli infections,” Hotez said.

Shelters could also pose a public health risk, said Dr. Amesh Adalja, a senior associate at the Johns Hopkins Center for Health Security.

“If you are in a small enclosed area in an alternate care facility and you have really bad diarrhea, it’s going to be hard in these situations to practice proper infection control.”