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WASHINGTON (AP) – A heavy rainfall in upstate New York washed bacteria from a cattle barn into the water supply at a county fair, causing a death and more than 100 illnesses two years ago. Now, researchers have discovered that such events are more common than people had thought.

Scientists at Johns Hopkins University in Baltimore reported Tuesday that more than half of all waterborne disease outbreaks in the United States during the last half-century followed a period of heavy rainfall.

Some 51 percent of the outbreaks were preceded by a rainstorm ranking in the top 10 percent of storms for the area during that period. And 68 percent of the outbreaks followed storms ranked in the top 20 percent, they said in a paper in the American Journal of Public Health.

While heavy rains and subsequent runoff have been assumed to be a factor in the transport of bacteria, the study is the first quantitative analysis of the relationship, the team said.

“We were quite struck by the strong relationship between rainfall and subsequent waterborne disease outbreaks,” said Dr. Jonathan Patz, who led the research team.

Mary Fran Myers, co-director of the Natural Hazards Center at the University of Colorado, said she had not seen any similar studies.

Patz said there are two messages in the report: “One is that our current water facilities do need to be improved, and even today when we have heavy rainfall there is a public health risk.”

“There are 950 communities still in the United States that have antiquated (sewer) systems, so that when you have heavy rainfall, the storm water, which is handled in the same system as sewage, you get overflows and you get contamination,” he said in a telephone interview.

“The significance of the association between precipitation and disease is amplified when you consider the effects of global climate change, which predict an increase in precipitation in parts of the United States,” added Patz, assistant professor of environmental health sciences.

The researchers at the Johns Hopkins Bloomberg School of Public Health studied 548 outbreaks of waterborne disease between 1948 and 1994 as reported by the Environmental Protection Agency and Centers for Disease Control and Prevention.

The most common type of outbreak was acute gastrointestinal disease.

That was the case in the 1999 outbreak at the Washington County fair in upstate New York, where dozens of people were hospitalized after contacting E. coli bacteria in contaminated drinking water.

The scientists compared the places and dates of the outbreaks with rainfall records for the nation’s various watersheds collected by the National Climate Data Center.

There were 133 disease outbreaks originating from surface water such as lakes and rivers, and the team found that they followed strong storms that occurred the month of the outbreak or the month before.

There was a longer lead time, up to three months, for outbreaks involving ground water such as wells or aquifers. Those sources accounted for 197 outbreaks.

In the remaining 218 outbreaks, it was not known if the water came from a ground or surface reservoir.


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