Auburn, Jan. 24---A specter is haunting the nation’s drinking water supply: the specter of Cryptosporidium.

Cryptosporidium parvum is a small, crude and potentially deadly pathogen. Scientists have known about it since 1907 but were not aware of its effects on humans until 1976. Nine years later in 1987, cryptosporidium sickened more than 13,000 people in Carrolton, Ga. Scientists traced the outbreak back to the municipal water supply – surprising, considering that the water met all state and federal safety standards.

The most memorable case occurred 6 years later in Milwaukee, when an outbreak sickened an estimated 400,000 people, contributed to the deaths of more than 50 AIDS and chemotherapy patients and resulted in the loss of more than $37 million in lost wages and productivity. Like the Carrolton outbreak, the problem was traced to the local drinking water supply.

Cryptosporidium is like few other waterborne pathogens, which explains why it can survive rigorous disinfection and why scientists are so worried about it.

"Cryptosporidium parvum is extremely troublesome for a number of reasons," says Dr. Jim Hairston, an Alabama Cooperative Extension System water quality scientist and Auburn University professor of agronomy and soils.

"It can exist outside its host in a tough egg-type structure called an oocyst, which can cause infection once it’s been ingested by humans and host species," he adds.

Equally disturbing, Hairston says, is the fact that scientists are not sure how long these oocysts can survive under a wide range of environmental conditions.

"They are very resistant to the most common detergents and disinfectants," he says, adding that even commonly recommended sanitary procedures will not always prevent their spread.

Oocysts, for example, are not killed by many common household disinfectants, including bleach. In fact, they can survive for up to two hours in common household bleach at room temperature.

Even chlorination, the method most commonly used by water treatment plants to cleanse water of potentially harmful pathogens, will not kill the oocysts. That is why public water utilities throughout the nation are developing new techniques to ensure drinking water is safeguarded from this pathogen.

Physical removal of particles has traditionally been an important step in treating drinking water. Following the Cryptosporidium outbreak in Milwaukee, water-treatment authorities throughout the nation stepped up efforts to improve their micro-filtration system to reduce risk of oocysts turning up in the drinking water supply.

Ozone and ultra-violent light are also effective against Cryptosporidium oocysts, though these techniques are very expensive and cannot safeguard the water against additional exposure that may occur as the water moves beyond the treatment facility and further along the distribution chain.

Currently, no drug is available to treat Cryptosporidiosis, the disease that can occur when the oocysts are ingested. The good news is that Cryptosporidiosis poses no threat to healthy people, other than a few days of diarrhea, nausea and cramping.

People with compromised immune systems are a different matter. The effects of prolonged diarrhea and dehydration can be dangerous and, in some cases, even deadly.

The elderly as well as AIDS and chemotherapy patients need to be especially aware of the risks associated with Cryptosporidiosis.

The risk of waterborne Cryptosporidiosis from public drinking water varies depending on the quality of the source water and the type of water treatment.

People with compromised immune systems should consult their local health authorities to determine the risk in their area.

In areas where chance of a Crytosporidium outbreak is relatively high, AIDS patients and others with weakened immune systems should consider disinfecting their water by bringing it to a rolling boil for at least one minute. The pathogen also can be removed with point-of-use filters, although only filters with an absolute (not minimum) pore size of one micron or smaller will ensure removal.