Photograph by Justin Lane, European Pressphoto Agency

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Two men stand by as water is pumped out of a basement in Sandy-slammed Manhattan on October 30.

Photograph by Justin Lane, European Pressphoto Agency

How Superstorm Sandy's Floods Can Make You Sick

Standing water may put New York City residents in danger of infections.

As much of the U.S. Northeast grapples with the inundation of Hurricane Sandy, the most dramatic photos show standing water filling busy U.S. streets in New York CityNew Jersey, and along the coastline.

Public health officials caution that stagnant water from floods can pose significant health risks, many of which can worsen with time. (See "Hurricane Sandy: Why Full Moon Makes 'Frankenstorm' More Monstrous.")

David Doyle, a spokesperson for New York's Office of Emergency Management, cautioned that flood debris can hide broken bottles and even animals. He also urged people to avoid moving water, noting that just 6 inches (15 centimeters) of it can sweep someone off their feet.

New York Mayor Michael Bloomberg said Tuesday that flooding would be addressed promptly, but urged residents to avoid contact with the water, portions of which may have been electrified by downed power lines.

Urban runoff in large cities is generally considered safer than rural runoff, which can include animal fecal bacteria produced from agriculture. Yet urban sewage treatment plants that are overwhelmed during major flood events can spill untreated sewage into waterways. It can then end up on streets and clog storm drains. Other urban contaminants include motor oil, gasoline, and trash.

Untreated Sewage a Danger

Joan Rose, the Homer Nowlin Chair in Water Research at the University of Michigan, who specializes in microbial risks, noted that untreated sewage can introduce bacteria, viruses, and parasites capable of causing a variety of ailments. "With the cool temperatures [in New York City], these pathogens can survive for months," she said.

Cases of vibrio bacteria infections, which enter the body through open cuts, were reported after Hurricane Katrina devastated New Orleans and surrounding areas in 2005, Rose noted. Even boaters and kayakers can pick them up. (Watch hurricane videos.)

Potential infections were easily picked up from parasites in the water following Hurricane Katrina, which hit the U.S. Gulf Coast.

New York's risk might be even greater in certain places, considering the thousands of tons of raw sewage that have flowed into the Hudson River.

To avoid risks of contacting harmful contaminants, the U.S. Federal Emergency Management Agency has advised those affected by the aftermath of Hurricane Sandy to adhere to local warnings to boil tap water.

New York City officials have also asked that residents in the lower half of the island remain in their homes until street water can be adequately diverted into local waterways.

E. Coli the Bacteria to Watch

The most concerning urban bacteria is Escherichia coli—also known as E. coli—the organism that most mammals use for digestion. Found in the lower intestine, it can be toxic if ingested into the stomach. Floods that carry raw sewage into high density areas can spread the bacteria. (Explore an interactive of the human body.)

E. coli is consumed by either drinking contaminated water or eating food with the bacteria. The resulting condition is known as gastroenteritis, a common ailment among Western travelers in developing countries.

Earlier this year, the Union of Concerned Scientists published a report outlining the risks of urban flooding, highlighting that the occurrence of floods may increase due to global warming. Driving on inundated streets was identified as the top safety risk, but sitting water produces significant health risks as well.

Flooding can overwhelm potable water infrastructure, preventing water purification. Overwhelmed infrastructure can also lead to sewage backups and mold growth, which can cost a city billions of dollars to fix. (See flood pictures.)

Health risks can be dramatically minimized with a timely cleanup. "Things definitely get worse with time," said Liz Perera, a co-author on the report and an environmental scientist and policy analyst with the Sierra Club.

"As water stagnates, the E. coli bacteria can spread. Other types of bacteria and parasites can spread," said Perera.

Floods Almost Always Spike Illnesses

Even without directly drinking the brackish water, contaminants can make their way into human bodies, through the air, or even through the faucet. Just walking through open water can infect people with open cuts. Rubbing eyes after touching water can increase one's risk of infection as well.

"In almost every situation after each flood there is some evidence of increased illness, though it's not always well documented," said the University of Michigan's Rose.

A 1993 study of Milwaukee, Wisconsin's public health system found that after the city had received heavy rainfall and floods in busy areas, the outbreak of gastrointestinal diseases treated in regional hospitals increased sharply. Children were much more affected than adults. In all, 400,000 people in Milwaukee's metro area were infected. More than a hundred deaths were reported.

To limit risk, Rose suggests avoiding anything exposed to floodwater. She advises prudent hand washing and staying current on the tetanus vaccine. (Get our tips on hurricane preparedness.)

One helpful influence in combating flood toxins is often sunlight, which can help neutralize dirty water with ultraviolet light. "That can be nature's way of cleansing water," said Nancy Hall, a professor of environmental microbiology at the University of Iowa.

But with significant water in the streets, and especially in New York City, where direct sunlight is often blocked by large skyscrapers, the water's conditions can deteriorate. Said Hall, "Some of the disease-producing organisms would probably survive for quite a while."