WQ-23
Cryptosporidium (crip-toe-spor-ID-ee-um) is a protozoan, a single-celled parasite that lives in the intestines of animals and people. This microscopic pathogen causes a disease called cryptosporidiosis (crip-toe-spor-id-ee-Osis).
The dormant (inactive) form of Cryptosporidium, called an oocyst (O-o-sist), is excreted in the feces (stool) of infected humans and animals. The tough-walled oocysts survive under a wide range of environmental conditions.
The most common symptom of the disease is watery diarrhea. There may also be abdominal cramps, nausea, low-grade fever, dehydration, and weight loss. Symptoms usually develop 4 to 6 days after infection but may appear any time from 2 to 10 days after infection.
People with healthy immune systems are usually ill with cryptosporidiosis for several days but rarely more than two weeks. Some infected individuals may not even get sick. Some people with cryptosporidiosis seem to recover, then get worse again. Those who are infected may shed oocysts in their stools for months, even after they no longer appear to be ill.
Cryptosporidiosis may cause complications for those with illnesses or conditions such as diabetes, alcoholism, or pregnancy. The effects of prolonged diarrhea and dehydration can be dangerous, especially for the very young, the elderly, and the frail. Cryptosporidiosis is most severe and long-lasting in immunocompromised individuals (those whose immune systems are weak), such as people infected with HIV (the virus that causes AIDS), cancer patients on chemotherapy, transplant patients, or others taking medications that suppress the immune system. This disease can be life-threatening for the immunocompromised.
Cryptosporidiosis cannot be diagnosed by symptoms alone. Watery diarrhea is a symptom of many intestinal diseases caused by bacteria, viruses, or parasites. If Cryptosporidium is the suspected cause of an intestinal illness, the doctor should request a specific diagnostic test.
There is currently no drug that can cure cryptosporidiosis. People with competent immune systems will recover on their own and appear to develop some immunity to sub-sequent infections. Antidiarrheal medicines may ease some of the symptoms. Anyone with diarrhea should drink plenty of fluids to prevent dehydration.
You can get infected with Cryptosporidium when you put anything in your mouth that has been in contact with feces from an infected animal or person. When large numbers of people get cryptosporidiosis, the source of infection can sometimes be tracked down, but it is impossible to determine the origin of many individual cases of this disease. Your hands may be contaminated with Cryptosporidium through person-to-person contact, perhaps while changing a child's diaper, caring for someone with diarrhea, or engaging in any activity that involves touching areas of the body contaminated with feces. Cryptosporidiosis can be easily spread among people in close social groups such as families, day care centers, and nursing homes. People who work with animals, especially young animals or animals with diarrhea, have a greater chance of exposure to the parasite. You may pick up oocysts while handling a litter box, soil, or any object contaminatedwith even a small amount of feces.
You can also get cryptosporidiosis by drinking water or eating food that has been contaminated with oocysts. Drinking untreated surface water (such as streams, rivers, and lakes) or swallowing a small amount of water when swimming, even in a chlorinated pool, can causecryptosporidiosis. The parasite may also be spread in uncooked foods, beverages, or ice prepared with contaminated water. Unwashed fresh fruits or vegetables may carry oocysts if manure was used or animals grazed where the crop was grown.
People who are infected (or whose hands become contaminated) with Cryptosporidium can spread the disease to other people or pets if they are not careful about their hygiene. Frequent handwashing is the single most important thing people can do to avoid spreading cryptosporidiosis and other illnesses. It is especially important to wash thoroughly before preparing food, as well as after using the toilet.
Oocysts are not killed by typical household disinfectants,including bleach, but are killed at temperatures greater than 160o F (hotter than most domestic hot tap water). Thorough drying in a clothes dryer will kill oocytes by desiccating them.
Cryptosporidiosis has long been a veterinary problem, predominantly in young farm animals such as calves. Cryptosporidium was first recognized as a cause of human disease in 1976 but was rarely reported in humans until 1982. The number of detected cases began to rise rapidly along with the AIDS epidemic and the development of methods to identify the parasite in stool samples. The earliest cases of human cryptosporidiosis were diagnosed in animal handlers. An outbreak at a day care center was first documented in 1983.
In 1987, 13,000 people in Carrollton, Georgia, became ill with cryptosporidiosis. This was the first report of its spread through a municipal water system that met all state and federal drinking water standards. In the spring of 1993 in Milwaukee, Wisconsin, municipal drinking water, again within standards, was contaminated with Cryptosporidium. An estimated 400,000 people became ill, and the disease contributed to the deaths of some AIDS patients. These outbreaks focused attention on the risk of waterborne cryptosporidiosis and the possible need for stricter drinking water standards.
We do not know exactly how many cases of cryptosporidiosis actually occur. Many people do not seek medical attention or are not tested for this parasite and so Cryptosporidium often goes undetected as the cause of an intestinal illness. Health professionals in some states are on the lookout for cases of cryptosporidiosis through surveillance programs at hospitals, clinics, and labs. The Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, keep track of many diseasecausing organisms and sendout warnings and advice on controlling outbreaks to every health department in the United States.
Oocysts are present in most surface bodies of water (e.g.,lakes, rivers) across the United States, many of which supply public drinking water. Oocysts are more prevalent in surface waters when heavy rains increase runoff of wild and domestic animal wastes from the land or when sewage treatment plants are overloaded or break down. Only laboratories with specialized capabilities can detect the presence of Cryptosporidium oocysts in water.
Unfortunately, current sampling and detection methods are unreliable. It is difficult to recover oocysts trapped on the material used to filter water samples. Looking at asample under a microscope, it is not easy to determine whether an oocyst is alive or whether it is the species Cryptosporidium parvum that can infect humans.
The number of oocysts detected in raw (untreated) water varies with location, sampling time, and laboratory methods. Water treatment plants remove most but not always all oocysts from municipal drinking water. It is not known exactly how many oocysts are sufficient to cause cryptosporidiosis, but the low numbers of oocysts sometimes present in drinking water are not considered cause for alarm in the general public.
Multiple barriers are needed to protect our water sup-plies from Cryptosporidium. Water treatment methods alone cannot solve the problem; watershed protectionand monitoring of water quality are critical.
Cryptosporidium oocysts have tough walls that can withstand many environmental stresses and are resistant to the chemical disinfectants such as chlorine that are traditionally used in municipal drinking water systems and swimming pools. Physical removal of particles, including oocysts, fromwater by filtration is an important step in the municipal water treatment process. Typically, water pumped from rivers or lakes into a treatment plant is mixed with coagulants that help settle out particles suspended in the water. If sand filtration is used, even more particles are removed. Finally, the clarified water is disinfected and piped to customers. Filtration is the only conventional method now used in the United States for controlling Cryptosporidium.
Ozone is a strong disinfectant that kills protozoa if sufficient doses and contact times are used, but ozone leaves no residual for killing microorganisms in the distribution system, as does chlorine. The high costs of new filtration or ozone treatment plants have to be weighed against the benefits of additional treatment. Even well operated water treatment plants cannot ensure that drinking water will be completely free of Cryptosporidium oocysts.
Watershed protection is another barrier to Cryptosporidiumin drinking water. Land use controls such as septic system regulations and best management practices to control runoff can help keep human and animal wastes out of the water. Water treatment and monitoring regulations Under the Surface Water Treatment Rule of 1989, public water systems are required to filter surface water sources unless water quality and disinfection requirements are met and a watershed control program is maintained. This rule, however, did not address Cryptosporidium. The U.S. Environmental Protection Agency (EPA) has set standards for turbidity (cloudiness) and coliform bacteria (which indicate that pathogens are probably present) in drinking water. Frequent monitoring is required so officials will have an early warning of potential problems and can take steps to protect public health. Unfortunately, there are no water quality indicators that can reliably predict the occurrence of cryptosporidiosis. More accurate and rapid assays for oocysts will make it possible to notify residents promptly if their water supply is contaminated with Cryptosporidium and thus avert outbreaks.
Efforts are under way to answer questions about the occurrence, detection, and treatment of Cryptosporidium in water so that the EPA and states can set specific standards for this parasite in the future. The collaborative efforts of water utilities, government agencies, healthcare providers, and individuals are needed to prevent outbreaks of cryptosporidiosis.
Properly drilled and maintained wells that tap into groundwater are unlikely to contain pathogens because of the natural filtration that takes place as water percolates down through the soil. But contaminants may flow into groundwater aquifers that lie beneath coarse soils or fractured bedrock. Very shallow or poorly constructed wells and springs can be contaminated with surface water runoff that carries disease-causing microbes. It is important that the well be protected from surface contamination by an intact well casing, proper seals, and a cap above ground.
The risk of waterborne cryptosporidiosis from public drinking water varies depending on the quality of the source water and type of water treatment. HIV-infected persons should follow the guidelines issued by the CDC and talk with their health care providers about safe drinking water. When routine testing of public drinking water indicates potential danger, the health department or water utility will issue a "boil water" notice.
There are three measures you may wish to take to ensure that your drinking water is safe: boil your water to kill the pathogen, remove oocysts from your water with certain types of filters, or drink certain types of bottled water. Boiling water is the best method of killing Cryptosporidium and other waterborne pathogens; water should be brought to a rolling boil for at least one minute. It should be stored in the refrigerator in a clean bottle or pitcher with a lid. To prevent recontamination, be careful not to touch the inside of the water bottle or lid.
Water can be filtered to remove Cryptosporidium oocysts and the cysts of another protozoan parasite, Giardia lamblia. Point-of-use filters may be used to treat the water for drinking or preparing foods. They may be either attached to a faucet or have a pour-through design. Only filters with an "absolute" (not "nominal") pore size of one micron (1 u) or smaller will remove all the oocysts(viruses, however, can pass through a 1 u filter). The pores of reverse osmosis (RO) membranes are too small for oocysts to pass through. NSF International, an independent, nonprofit testing agency, publishes lists of filters and RO units certified for "cyst reduction." Follow the manufacturer's instructions that are supplied withwater treatment equipment to prevent clogging and ensure proper filtration. The filter cartridge(s) and membrane will need to be replaced periodically. Improper maintenance can actually increase health risks.
Under current standards, bottled water is not necessarily any safer than tap water. Bottled water from deep wells (groundwater sources) has a very low likelihood of containing oocysts, but bottled water from a surface water source has the same risk of containing oocysts as tap water from that source unless it is treated before bottling.
Read the label on bottled water for information about the water source and treatment. Water can be distilled or pasteurized to kill all pathogens before bottling. Procedures for using ozone to inactivate oocysts in bottled water have not yet been established. Oocysts can be removed by reverse osmosis or a filter with an absolute one-micron rating. Other microfiltration or ion-exchangemethods or treatment with chlorine, carbon dioxide, or ultraviolet light cannot promise crypto-free water.
The heat of pasteurization will kill all pathogens in dairy products. Bottled and canned bubbly drinks such as sodas and beer are usually heated or filtered enough to kill or remove Cryptosporidium.
You can minimize the chances of getting infected with Cryptosporidium (and numerous other pathogens) by always practicing good hygiene, especially after possible exposure to sources of infection. People with compromised immune systems must consistently take precautions to avoid exposure to Cryptosporidium.
The information in this fact sheet is not intended as medical advice for individual problems.
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This publication was originally produced by Media Services at Cornell
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