Climate Change May Impact Waterborne Diseases

"Cryptosporidiosis is one of many waterborne diseases whose prevalence could increase with increased precipitation and flooding triggered by climate change," says Dr. Patricia L. Kocagil, postdoctoral associate in agricultural economics.

According to the Centers for Disease Control in Atlanta, Cryptosporidium parvum, a protozoan parasite, was first recognized in 1976 as producing illness in humans. Causing a diarrheal disease that lasts for one to two weeks in healthy individuals, Cryptosporidium can be fatal among immunocompromised persons.

The researchers, who include Kocagil; Dr. Ann Fisher, senior scientist; and Dr. James Shortle, professor of agricultural economics, are looking at Lancaster County, Pa., to evaluate and assess the problems and costs associated with Cryptosporidiosis outbreaks and the increased risks with global warming.

"So far, there is no medication to cure Crypto, tests for the organism are not routinely done on water supplies, and current detection technology is not always reliable," says Kocagil.

Evaluating what is known about this disease, the researchers told attendees at the spring meeting of the American Geophysical Union Meeting today (May 26) that the cost to society of a current outbreak is about $211 per person. This includes the actual costs of medical care, such as the costs of medication, hospitalization and physicians' services, as well as the cost of time lost from work and leisure activities. Added to that is the cost of trying to avert an outbreak with "boil water" edicts and purchasing or hauling water.

"But this is for an outbreak today, under current circumstances," says Kocagil. "Things could change as climate changes."

Even today, an outbreak can be costly in both dollars and human suffering. In 1993, during an outbreak in Milwaukee, Wisconsin, 400,000 people became ill.

One problem assessing the impact of this disease in an altered climate regime is the prevalence of very tiny Cryptosporidium oocysts -- the protozoan equivalent of a fertilized chicken egg. Reservoirs for Cryptosporidium exist in livestock, such as cattle and dairy cows and wildlife such as deer. Runoff from agricultural areas can release the Cryptosporidium oocysts into the drinking water supply.

Another problem is that the standard purification approach for drinking water in the United States, chlorination, has little effect on the organism. Filtration can remove the oocysts, but because of their small size, filters must be properly monitored and managed. The U.S. Environmental Protection Agency is currently proposing expanding water treatment requirements to safeguard water supplies from Cryptosporidium.

"We are looking at a situation where there is no known medical cure, where water treatment must be closely monitored because standard purification methods do not work, where testing of water is not routinely carried out and where routine screening for the disease only takes place in previously immunocompromised individuals," says Kocagil. "What happens now if global warming increases the frequency of a 100-year flood to every 50 years?"

The researchers have estimated that doubling of the frequency of 100 year floods could add up to $70 to the per person cost under certain conditions.

"Part of the problem is that we do not know how prevalent this disease is now," says Kocagil. "Many people do not go to the doctor with diarrheal diseases that clear up on their own."

It was only in 1982, when the number of cases among HIV-infected people began to rise that outbreaks among immunocompetent people were reported.

What level of oocyst in the water is acceptable? Should all drinking water sources be tested? Should tests for Cryptosporidium become routine in diarrheal outbreaks? When should a "boil water" directive be issued and when should one be rescinded?

"There are gaps in scientific understanding and available data for assessing the magnitude of drinking water health threats today," says Kocagil. "This makes it very difficult to assess the drinking water problems under a global warming scenario."