What is Cryptosporidium ?
Cryptosporidium (krip-toh-spo-rid-ee-um) is a microscopic, disease-causing parasite that lives and reproduces in the intestines of cattle, sheep, deer, beavers, dogs, cats, squirrels and other animals. It can also live in humans. Outside of a host, Cryptosporidium lives in a hard, protective shell called an oocyst. It can survive this way in the environment for several weeks.
The parasite was discovered in animals around the turn of the century, but no one knew it could make humans sick until the mid 1970’s. Not much was heard about Cryptosporidium until several outbreaks of waterborne illnesses occurred in the U.S. in the 1980’s. Cryptosporidium drew national attention in 1993 when an outbreak of waterborne disease in Milwaukee, Wisconsin sickened 400,000 people and killed over 100 people with weakened immune systems.
If swallowed, Cryptosporidium can cause an intestinal illness called cryptosporidiosis in animals and humans, for which there is currently no effective medication. Symptoms include diarrhea, cramps, headaches, nausea, vomiting and fever. For most people, symptoms take 2-12 days to appear and last 10-14 days, until a person’s immune system fights off the infection.
How can a person be exposed to Cryptosporidium?
Exposure to Cryptosporidium occurs through contact with feces or fecal contamination. Cryptosporidium contact has happened in daycare centers and hospitals; through contact with animals; through eating undercooked, contaminated food and drinking water contaminated with animal waste or sewage. Current data are not sufficient to determine how most people become infected. In the absence of a widespread outbreak of cryptosporidiosis as in Milwaukee, it can be difficult to trace the source of contamination.
What is the risk of waterborne Cryptosporidium infection?
According to the Centers for Disease Control, Cryptosporidium does not pose a serious health threat for the vast majority of Americans. For people with severely weakened immune systems, however, the risk of infection is higher. For them, cryptosporidiosis can last for months and can be fatal. Those with severely weakened immune systems include people with AIDS, people who are HIV-positive, cancer patients and organ transplant recipients on immunosuppressive drugs, malnourished children and those born with weak immunity. Cryptosporidium has been a contributing cause of death in some immunocompromised people.
While some people are more vulnerable to Cryptosporidium infection, not everyone who is exposed to the parasite gets sick. And not all strains of Cryptosporidium cause disease in humans. Further, scientists are uncertain how many oocysts must be ingested to cause infection. Many studies are underway to find answers to the health questions surrounding Cryptosporidium.
Is Cryptosporidium common in water?
Because many animals carry Cryptosporidium, it is common in both soil and untreated water. Lakes, rivers and streams can become contaminated by runoff which contains waste from infected animals Wildlife can also contaminate water. Research shows that Cryptosporidium can be found in 97% of surface water in the U.S. The amount of the parasite in water sources varies widely. Groundwater can, but is much less likely to, contain Cryptosporidium.
Because Cryptosporidium is small enough to pass through conventional water plant filters and it is resistant to chlorine disinfection, even a well-run water treatment system cannot ensure that drinking water is completely free of the parasite. Some research shows that very low levels of Cryptosporidium can be found in about half of the treated water supplies in the U.S. According to the American Water Works Association Research Foundation, Cryptosporidium, where found, exists in water systems at less than 1 oocyst per 1,000 gallons of treated water. Ongoing studies show it can take ingesting anywhere from 10 to 300 oocysts to cause infection. At the lowest dose, a person with a normal immune system would have to drink 10,000 gallons of water in a short period of time to swallow an infectious dose of Cryptosporidium. To further put the risk of infection in perspective, people generally drink less than 5 gallons of every 1000 gallons of treated water they use.
What about tests for Cryptosporidium?
Unfortunately, tests for Cryptosporidium are not conclusive. Unlike contaminants that dissolve in water, Cryptosporidium oocysts are individual objects. Looking for them in concentrated water samples under a microscope is like looking for a needle in a haystack of other particles. Finding Cryptosporidium does not tell whether the oocyst is alive or dead, infectious or not. Oocysts also look like some algae under the microscope. Failure to find Cryptosporidium in a test sample does not mean that none is present in the larger water supply. Further, the current tests for Cryptosporidium are costly and difficult; very few laboratories in the country are certified in Cryptosporidium testing and the difficulty in reproducing test results may lead the EPA to abandon certification.
The current tests are also time consuming and not very useful from a health perspective. By the time results are available for a sample of treated water (several days), that water has already been used by the community and is no longer in the pipes.
Why is Cryptosporidium more of a challenge to water providers than other harmful microbes?
Adding chlorine to drinking water kills most all harmful bacteria and viruses that may be in water. But unlike these other pathogens, Cryptosporidium is resistant to chlorine. Because Cryptosporidium is hard to kill and testing for it is not very helpful or conclusive, water suppliers must do everything they can to remove it from water before delivering the water to customers.
How is Cryptosporidium removed from water?
Cryptosporidium is removed by a water treatment plant’s particle removal process. Studies have shown that the treatment process removes more than 97% of Cryptosporidium oocysts. However, because oocysts are so small, it is not possible to guarantee that none pass through conventional filters, one of the final steps in water treatment.
Three alternatives currently available to be certain that no Cryptosporidium remain in drinking water are (1) boil the water, (2) pass it through a filter with pores smaller than Cryptosporidium, or (3) put it through a process called reverse osmosis. Using any of these methods on a large scale is not reasonable or affordable for water suppliers. So suppliers must rely on a “multiple barrier” approach of watershed protection and optimized particle removal with careful water quality monitoring. (See the last question for additional measures that individuals may wish to take.)
How does the Roanoke Rapids Sanitary District reduce customers’ risk of contacting waterborne Cryptosporidium?
It has always been our policy to be proactive and do whatever is possible to ensure the safety of the community’s water. The District supports a strong program of multiple barriers to prevent water contamination from Cryptosporidium and other pollutants.
· Watershed Protection
Our first line of defense is watershed protection – keeping contaminants out of the water supply.
The natural dynamics of the Roanoke Rapids Lake itself provides a barrier to Cryptosporidium. Reservoirs carry less suspended runoff than rivers and give contaminants such as Cryptosporidium time to settle out or die. The additional barriers provided by the upstream lakes – Kerr and Gaston provide additional protection for the District’s water source.
Protective programs enacted by county government should provide important elements in drinking water protection: low density development requirements and assistance to farmers in properly managing runoff and animal waste.
· Optimized Water Treatment & Monitoring
The next major barrier to Cryptosporidium is the water treatment process. The vast majority of solid particles are removed from water through the induced clumping of particles and the sinking and removal of these clumps, in which Cryptosporidium oocysts are trapped.
Next, the water flows through multi-layer filters which remove most of the remaining particles. District operators backwash these filters to cleanse them of trapped particles. The Cryptosporidium outbreak in Milwaukee was caused in part by inadequate filter washing and in part by use of less effective clumping chemicals. This summer, the District completed a complete renovation of its filter system including all chemical feed equipment.
A crucial part of the water treatment process is careful water quality monitoring. The District has devices called turbidity monitors which are connected to each water filter and measure the cloudiness of the water and tells how well the filters are working. Low turbidity means that few particles remain in the water. The District maintains turbidity levels below the required standards.
In the event of unusually high turbidity readings, the District would issue a “boil water” alert to the community. High turbidity means that many particles are passing through the filters. Milwaukee’s Plant had high turbidity readings for several days prior to the outbreak of cryptosporidiosis. High turbidity does not necessarily indicate that Cryptosporidium is in the water, but it does mean the risk is higher.
What regulations exist for Cryptosporidium?
Because of the uncertainty surrounding the parasite, there are currently no federal regulations for Cryptosporidium. Efforts are underway by the EPA, Centers for Disease Control, and the American Water Works Association to resolve the uncertainties and enable EPA to set specific safety standards. If reliable, reproducible data on Cryptosporidium cannot be compiled, the EPA may not be able to set specific standards for the parasite and may set additional treatment performance standards instead.
What steps can individuals take to further reduce the risk of contacting waterborne Cryptosporidium?
Contact with Cryptosporidium can occur in a variety of ways, including contaminated water. Persons most at risk of contracting cryptosporidiosis are those with severely weakened immune systems.
On June 15, 1995, the U.S. Environmental Protection Agency and the Centers for Disease Control issued a joint statement entitled “Guidance for People with Severely Weakened Immune Systems.” In this statement, immunocompromised people are urged to talk to their health care provider about what extra precautions they may wish to take to minimize their risk of waterborne Cryptosporidium infection.
· Boiling Drinking Water
In the statement, EPA and CDC note: “Although data are not sufficient for [us] to recommend that all severely immunocompromised persons take extra precautions with regard to their drinking water, individuals who wish to take extra measures to avoid waterborne cryptosporidiosis can bring their drinking water to a rolling boil for one minute. Boiling water is the most effective approach for killing Cryptosporidium.”
· Water Filters
An alternative to boiling is using a point-of-use filter (for personal use at the end of a tap or under the sink). The only filters that remove Cryptosporidium are (1) those that use reverse osmosis, (2) those labeled “Absolute” one micron filters or (3) those labeled certified by NSF International under Standard 53 for “Cyst Removal.” Water treated with one of these filters will be free of organisms smaller than Cryptosporidium, but may not be free of organisms smaller than Cryptosporidium that could pose a health hazard for severely immunocompromised people. Filter users must follow the manufacturer’s instructions for use and replacement.
· Bottled Water
Another alternative to boiling is using some bottled waters. The source of a bottled water, the types of microorganisms in it, and the treatment of the water before bottling vary widely among bottled water companies and brands by the same company. One can not assume that all bottled water is free from Cryptosporidium. Those from protected wells or springs are less likely to be contaminated than bottled water containing municipal drinking water from less protected sources like lakes and rivers. Distilled bottled water or water treated with reverse osmosis before bottling assures that Cryptosporidium and other contaminates are removed.
The Roanoke Rapids Sanitary District cannot endorse the use of any particular product. For filter information, you can contact NSF at 1-800-NSF-8010 or write National Sanitation Foundation, 3475 Plymouth Road, P. O. Box 130140, Ann Arbor, MI 48113-0140.