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Cryptosporidium

Overview
 
CAS Number:
Synonyms: C. parvum, Cryptosporidium parvum
Contaminant Type: Microbial

Cryptosporidium occurs in many forms. Some species of the contaminant include C.bailey, C.hominis, C.meleagridis, C. muris, C.parvum and C.serpentis. Cryptosporidium oocysts contaminate most drinking water sources with the potential to cause disease outbreaks. It is a concern because the oocysts are resistant to the common chlorine and chloramine water disinfectants. [600]

Cryptosporidium oocysts are ubiquitous in source waters in the US. Principally related to livestock, C. parvum oocysts from deposited fecal matter can be picked up by run off over soil surfaces and transported to surface waters. The oocysts can also be transported though soil to ground water. They can persist in waters for extended periods of time. They can survive freezing better than survive 25 C. They have low specific gravity (about 1.05 g/cc) and are buoyant so that oocysts not bound to particles tend to float to the top of a water column. However, they are likely bound to organics and particulate surfaces and suspended in surface waters. [599]

Although other species may infrequently infect humans, most all Cryptosporidium infections in humans are caused by C. parvum. Cryptosporidiosis required only low infective dose in humans. C. parvum oocysts are pathogens completing their life cycle in the digestive tract of the host. Four sporozoites are released from each oocyst and parasitize cells of digestive surfaces. Resulting symptoms are self limiting in healthy adults with diarrhea, dehydration, cramps and fever lasting less than two weeks. It is more severe in people with weakened immune systems and sometimes fatal in people with compromised immune systems. [599]

Cryptosporidium oocysts were regulated under the Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR or LT1) to require microbial inactivation to ensure that microbial protection was not jeopardized when systems modified treatment to comply with the Stage 1 Disinfectants and Disinfection Byproduct Rule. [598] It required a 2-log removal of Cryptosporidium [598] in filtered water systems.

The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR or LT2) required additional treatment of oocysts for higher risk systems. [600] Higher risk systems include unfiltered systems and filtered systems with higher levels of Cryptosporidium in their source waters. Systems must monitor their source waters to determine their treatment requirements. Filtered systems are classified into one of four treatment categories or bins. With relatively low occurrence, no additional treatment is required. With relatively higher Cryptosporidium levels from monitoring, systems must further reduce Cryptosporidium levels by 1 to 3 logs depending on the bin and the type of filtration. Impacted systems can select treatment options from a microbial tool box depending on their bin. Unfiltered systems must achieve 2 or 3 log inactivation depending on the results of their occurrence monitoring. Uncovered finished water reservoirs must be covered or have the effluent treated to inactivate 2 logs.

Measurement of Cryptosporidium oocyst infectivity is complicated by methodology. Methods include in vitro excystation, infection of cell lines, morphological examination by microscopy, uptake of dyes, and animal infectivity; only the latter assures the oocyst is alive and infective in the host. [599]

In the Information Collection Rule (ICR) the Cryptosporidium detection method had relatively low recovery and used relatively small sample volumes. Results from the ICR survey indicated: (1) 43 percent Cryptosporidium detections (with poorer methodology) in sources of filtered plants, (2) Cryptosporidium levels higher in flowing streams than in lakes and reservoirs, and (3) as expected because unfiltered systems must meet higher quality source water standards to avoid filtration, filtered systems had higher source levels (mean 0.068 oocysts/L) than unfiltered (mean 0.002 oocysts/L). [599]

In the ICR Supplemental Survey (ICRSS), which surveyed only filtered plants, the method had relatively high recovery and used relatively larger sample volumes. Results from the ICRSS indicated: 85 percent Cryptosporidium detections (with better methodology) in sources of filtered plants, with mean 0.006 oocysts/L level. [599]

Date of literature search: April 2007



598 USEPA; 2002; Final Long Term 1 Enhanced Surface Water Treatment Rule; Final Long Term 1 Enhanced Surface Water Treatment Rule; EPA 815-F-02-001. Office of Ground Water and Drinking Water, USEPA, Washington, DC.
599 USEPA; 2005; Occurrence and Exposure Assessment for the Final Long Term 2 Enhanced Surface Water Treatment Rule; Occurrence and Exposure Assessment for the Final Long Term 2 Enhanced Surface Water Treatment Rule; EPA-815-R-06-002. Office of Ground Water and Drinking Water, USEPA, Washington, DC.
600 USEPA; 2007; Long Term 2 Enhanced Surface Water Treatment Rule (LT2) Basic Information; http://www.epa.gov/safewater/disinfection/lt2/basicinformation.html; As posted on August 28, 2007. Office of Ground Water and Drinking Water, USEPA, Washington, DC.



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