MONDAY, Aug. 6, 2001 (HealthDayNews) -- Floods are hazardous to your health, and not just for the obvious reasons. They can also wash bacteria and viruses into the water supply and cause outbreaks of intestinal disease. New research now suggests that such risks to humans may last for months after a storm.
Because global climate changes are expected to trigger heavier rains in some areas, "this particular health risk is something water managers need to anticipate," said Dr. Jonathan Patz, a professor at Johns Hopkins Bloomberg School of Public Health and lead investigator of the new study.
A variety of viruses, bacteria and parasites can make their way into drinking water and sicken people. In the 70 years that health officials have been tracking such events, the most famous outbreak in the United States occurred in Milwaukee in 1993, when more than 400,000 people were sickened by an outbreak of the parasite Cryptosporidium. By the time it ended, more than 100 people had died and 4,000 ended up in the hospital.
The liver-damaging hepatitis virus and the diarrhea-causing organism Giardia lamblia may lurk in the water supply, too. Even gastrointestinal complaints commonly caused by Escherichia coli can spring from water.
For the new study, researchers looked at 548 reports between 1948 and 1994 of water-borne illnesses that sickened at least two people per incident. They then compared the reports to rainfall in the regions at the time.
Heavy rainfall preceded more than half the outbreaks. Groundwater contamination popped up as long as three months after the flooding, but the lag time was much shorter for surface water contamination.
The findings are reported in the August 2001 issue of the American Journal of Public Health.
Flooding can cause epidemics in a variety of ways, Patz said. For one, contaminants like animal waste and leakage from septic tanks can be carried into saturated earth and enter the groundwater below. Rain can also wash contaminants into lakes and streams.
Heavy rain preceded the Milwaukee outbreak and may have sent human or animal waste into the city's water supply, Patz said.
Also, he added, water treatment systems can become overloaded and fail. "When you get heavy rainfall, you get cloudy water that can clog filtration plants," he said.
Another problem arises when cities or towns combine their sewage and storm-runoff disposal systems. Flooding can cause the systems to back up, sending sewage into the environment, Patz said.
About 900 communities in the United States still have systems that combine sewage and runoff, despite government attempts to make them upgrade.
The study points up the importance of modernizing water systems, Patz said, although the research didn't look at whether the old water systems posed a special risk.
On the whole, he added, the country's water systems are in good shape. "But there's still a risk [of disease] even today in the United States."
An expert in water-borne diseases questioned whether the findings of the Johns Hopkins study are anything new.
The dangers of flooding are "certainly well recognized," said Mark LeChevallier, director of research for American Waterworks Service Company, which runs water systems in 23 states.
But it's not clear whether rainfall could have anything to do with outbreaks three months later, he said. Although heavy rainfall can increase contamination of the water supply, it should also start to dilute it after a while, he added.
But, he noted, there's no doubt that water systems should not mix sewage and storm run-off.
"When there's a lot of rainwater coming in, it's not adequate to allow sewage to bypass the treatment plants," he said.
What To Do
If it rains heavily, you may want to check with your local water agency about possible contaminants, particularly if you live in a community that does not have a separate sewage disposal system.
If you do suspect there are germs in your water, boil it for five or 10 minutes. Adjust the time if you're at a high elevation. Here's a complete advisory on how to clean water from the Red Cross.
Learn about the deadly parasite Cryptosporidium from the U.S. Agricultural Research Service.
Learn about water safety from the National Environmental Education & Training Foundation.
