Whenever there are floods, there are health dangers, such as drowning, injuries, or electrocution. But even after the rain stops, the water left behind can pose health risks of its own.

Dr. Isaac Bogoch, a Toronto-based infectious disease specialist, says one of the biggest concerns is the accidental ingestion of contaminated water.

He notes that while the water that is flooding Texas and Louisiana was once clean rainwater, once it remains on the ground for any length of time, it can become contaminated with soil and vegetation bacteria, chemicals from vehicles and roads, and sewage from overflowing water treatment plants.

“Some will develop a diarrhea infection if they drink this water,” Bogoch told CTV’s Your Morning from Vancouver.

Among the bacteria that can cause stomach illnesses are salmonella, Shigella or E. coli; viruses such as rotaviruses and noroviruses, and parasites such as Giardia. All these pathogens can cause serious gastrointestinal illness that lead to vomiting, fever, diarrhea and dehydration.

Some of these infections are contagious and can even spread in the very evacuation centres where people have gone to escape the flooding’s health risks.

The contaminated water can also cause skin infections for those who wade into the water with abrasions on their skin.

“They’re usually minor and easy to treat but we might see more of them,” he said.

Skin infections

Environmental toxicologist Noreen Khan-Mayberry, who has been trapped in her home in Pearland, Texas, told CTV News Channel she’s worried by the number of people she’s seen playing in the water, seemingly unconcerned or unaware of the risks.

“There are so many strains of bacteria and viruses that are in that water,” she said.

Bacterial and fungal skin infections are common after flooding, she said, pointing to the surge of patients who developed skin lesions after Hurricane Katrina.

Many of those were caused by Vibrio vulnificus, a bacterium common in coastal areas and brackish ponds that can cause skin infections that take months to heal.

Trench foot is another infection that can come from spending too much time in the water, which can lead skin to break down, leading to blisters and open sores.

Khan-Mayberry said it’s so important for rescuers to take showers after being in the water.

“As soon as you get to a place where you can wash off with soap and water, that’s really going to decrease your chance of getting some skin infections that can show up days, weeks, or even months later,” she said.

Mosquito-borne illnesses

Even after the floodwaters recede, the health risks will continue, Bogoch said.

“There’s still going to be a lot of standing water around and this is a perfect breeding ground for mosquitoes,” he said, adding that could lead to more cases of mosquito-transmitted West Nile Virus.

In southern Texas, there is also the risk those mosquitoes could be carrying Zika virus, which poses a serious risk to women in early pregnancy.

Finally, there are worries about moulds that will grow in rain-soaked houses.

“Those aren’t terrible exposures and those risks are actually relatively low,” Bogoch said. “But some people might have an allergic reaction or some response to the moulds.”