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Monitoring for Cryptosporidium & Giardia

Cryptosporidium and Giardia are protozoa which cause the intestinal illnesses cryptosporidiosis and giardiasis, respectively. These diseases are transmitted by eating contaminated food, drinking contaminated water, swallowing contaminated water while swimming or bathing, having contact with animal or human feces, and certain sexual practices. According to the USEPA and the Centers for Disease Control and Prevention (CDC), it is unclear how most cases of cryptosporidiosis in the United States are contracted. Symptoms of infection include nausea, diarrhea, and abdominal cramps. Individuals who think they may have cryptosporidiosis or giardiasis should contact their health care providers.

Some people may be at greater risk from cryptosporidiosis and giardiasis than the general population. Immuno-compromised people, such as individuals undergoing chemotherapy; those who’ve undergone organ transplants or dialysis; and those with HIV/AIDS or other immune system disorders, can be at increased risk. These people should seek advice from their health care providers about taking steps to limit their exposure to the protozoa that cause infection. One of these steps includes boiling tap water for one minute. Other steps and guidelines on appropriate means to lessen the risk of infection by Cryptosporidium and other microbial contaminants via drinking water are available from the EPA’s Safe Drinking Water Hotline (800) 426-4791 and from CDC’s Cryptosporidiosis Fact Sheet.

For additional information, see the New York City Department of Health on-line fact sheets for giardiasis and cryptosporidiosis, EPA Office of Groundwater and Drinking Water, the Center for Disease Control, and NSF International for information on water filter certification. New York City’s Waterborne Disease Risk Assessment Program documents and tracks rates of giardiasis and cryptosporidiosis, along with demographic and risk factor information on case patients.

Cryptosporidium and Giardia Monitoring Program

The City began monitoring for the protozoa Cryptosporidium and Giardia in 1992 as part of its comprehensive watershed monitoring program. Today, over 1,000 routine samples are analyzed each year from nearly 100 sites. Samples are collected weekly from the Catskill and Delaware effluents of Kensico Reservoir and the effluent from New Croton Reservoir, prior chlorine disinfection. These sites are designated as New York City’s source water and are representative of the water distributed in the City. On occasion, DEP may collect protozoan samples at a higher frequency, such as during or after a heavy rainfall. This enhanced sampling is performed when a potential water quality event begins, and ends when the event is resolved.

Giardia cyst

Giardia cyst

Currently, DEP uses the USEPA approved Method 1623HV to analyze 50-Liter samples. Methods to sample and analyze Cryptosporidium and Giardia have changed and improved since 1992. Prior to switching methods, DEP conducted validation studies to demonstrate that the new method recommended by USEPA increased recoveries. Since recoveries from one method to the next were improved, results from the different methods may not be comparable. Additionally, the volume sampled has changed. Today’s method provides more frequent and slightly higher identification of Giardia and, to a lesser extent, of Cryptosporidium, but there is no indication of changes in water quality. These differences reflect improved recoveries. For reference, the ASTM D-19 P229 was first used in 1992, replaced for source water monitoring with USEPA ICR method in 1999, and with USEPA Method 1623HV (50-Liter volume) in October 2001.

Cryptosporidium oocyst


DEP’s Pathogen Laboratory was approved by USEPA to perform the USEPA ICR method, and more recently has also been approved to perform Method 1623 under the Laboratory Quality Assurance Evaluation Program for Analysis of Cryptosporidium in preparation of the Long-Term 2 Enhanced Surface Water Treatment Rule.

DEP works constantly to improve its monitoring and analytical methods, but there are deficiencies with the current water testing process. The method is not intended to determine whether Cryptosporidium and Giardia found in water samples are dead, alive or infectious. DEP is working with CDC to develop and use new analytical methods to identify the genotype of Cryptosporidium recovered from environmental samples. Genotyping provides information regarding the potential source of the oocysts. Results indicate that stormwater samples largely contain Cryptosporidium from wildlife sources. These results are important, because oocysts from non-human sources are unlikely to infect humans. Currently, there are no numerical drinking water standards for Cryptosporidium and Giardia. USEPA has proposed new regulations known as the Long-Term 2 Enhanced Surface Water Treatment Rule. Monitoring results with Method 1623HV indicate that New York City’s source waters are well below the treatment threshold required in the proposed regulations.

Evaluation of Water Quality Standards in Watershed Streams Using the Protocols of the DEC/DEP MOU, Addendum E

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