here is cause for concern about cryptosporidiosis in Nevada because the majority of the State's population and visitors are served by surface water which is susceptible to contamination by Cryptosporidium oocysts. The public health impact of an outbreak of cryptosporidiosis in terms of severity of disease and size of population affected in Nevada could be significant.

Not all surface waters in Nevada have been tested for Cryptosporidium. However, national studies indicate that the majority of surface waters in the country contain the organism. There are 30 public water systems (PWS) in Nevada that serve surface water and another 3 PWSs that have spring sources which are under the direct influence of surface water. The Nevada Division of Health (DOH), Bureau of Health Protection Services (BHPS) has identified another 8 PWSs in Clark County that have springs which may also be under the direct influence of surface water. Some PWSs are at higher risk than others because of the quality of their source water and degree of treatment. Findings of Cryptosporidium oocysts in Lake Tahoe and an increase in the number of cases of cryptosporidiosis amongst AIDS patients in Clark County during the first quarter of 1994 have heightened this concern.

The DOH (now the Nevada Division of Environmental Protection - NDEP) has taken the lead role in developing a statewide action plan. The NDEP is now responsible for assuring that Nevada's PWSs provide safe drinking water including complying with United States Environmental Protection Agency (EPA). NDEP now oversees compliance by PWSs that utilize surface water in the rural counties and Clark County. The Washoe County Health District (WCHD) has an interlocal agreement with NDEP to oversee compliance by surface water systems in Washoe County.

Drinking water is not the only route of exposure to Cryptosporidium. Cryptosporidiosis can be transmitted person-to-person and animal-to-person, typically by the fecal-oral route in which a person can become ill by coming in contact with the stool of an infected person or animal. Transmission can also occur by eating raw or undercooked food contaminated with Cryptosporidium. Ingestion of recreational waters contaminated with Cryptosporidium can also cause infection. The practice of good personal hygiene should be reinforced by the health authorities. This will reduce the risk of disease among the general public. However, individuals with compromised immune systems are at a risk of serious illness and a special effort should be made to inform these individuals about possible exposure to cryptosporidiosis from all sources, including their drinking water.

These individuals include, but are not necessarily limited to persons with the HIV virus, persons undergoing chemotherapy, persons who have recently had organ transplants, and persons suffering from certain viral illnesses. Infants and the elderly may also be considered a sensitive subpopulation because of their increased susceptibility to infection. However, persons with AIDS are the primary notification target group because cryptosporidiosis is a life-threatening disease for them. To date, the Health Divison and now NDEP is taking the following measures in response to concerns regarding cryptosporidiosis:

  • At the request of the Clark County Health District (CCHD), staff conducted an on-site investigation of the Southern Nevada Water System in response to an increase in the number of cases of cryptosporidiosis in AIDS patients in Clark County from December 1993 to March 1994.
  • Staff has met with CCHD and water suppliers in Clark County on 3 occasions to discuss options for addressing the increase in cryptosporidiosis cases amongst AIDS patients in Clark County.
  • Staff has become knowledgeable on Cryptosporidium through literature and attending training, including the Centers for Disease Control and Intervention (CDC) workshop in September, 1994.
  • Staff conducted a workshop in Carson City on December 6, 1994 for surface water suppliers in Northern Nevada to educate them on current knowledge about Cryptosporidium in drinking water. Follow-up workshops were also held in Carson City on February 14, 1995 and at CCHD on February 15, 1995. These workshops were conducted to finalize the public education initiative.
  • Staff made a presentation at the Nevada AIDS Task Force meeting in January, 1995.


It is intended that the action plan be based on a coordinated effort between the health authorities, water suppliers, medical community, and community based organizations. The plan requires coordination between DOH and NDEP: The Bureau of Laboratory Services (BLS) may also need to be involved by analyzing water samples collected by the health authorities and assisting in assuring that proper quality assurance/quality control procedures are being followed by contract laboratories. It is anticipated that the CCHD and WCHD will participate in all or parts of the final plan.

There are several important issues regarding the public health impact of Cryptosporidium in drinking water supplies. These issues have caused EPA to delay promulgation of the ICR and have hampered an effective public health response to date. These issues include:

  • The recovery efficiency of the current test methods for Cryptosporidium in environmental water samples is variable according to the quality of the water being tested. Only 5 to 50 percent of the organisms actually present in the sample are detected.
  • >Current test methods cannot differentiate infectious (viable) oocysts from non-infectious oocysts. It cannot be said with certainty that all oocysts found in a sample are capable of causing disease. Some may have been sufficiently damaged during the water treatment process to make them non-infective.
  • There is no known definitive infective dose-response relationship. Also, we do not understand the relationship between Cryptosporidium found in drinking water and cryptosporidiosis. Even in some outbreaks, the correlation between the concentration of Cryptosporidium in the implicated water and human illness has been poor. A recent New England Journal of Medicine article indicated that healthy adults can become infected by a low dose of Cryptosporidium parvum oocysts. The median infective dose was 132 oocysts.
  • The effectiveness of surface water treatment (i.e., filtration and/or disinfection), as required by current state and federal regulations in removing/inactivating Cryptosporidium is not fully known.


The Cryptosporidium Action Plan consists of the following elements: (1) Public Education, (2) Surveillance and Monitoring, (3) Water Treatment Optimization and Water System Improvements, and (4) Training of DOH and NDEP Staff on Cryptosporidium. This action plan is based on a variety of information sources, including the "Draft Work Group Reports" from the CDC Conference in September, 1994, and American Water Works Association (AWWA) guidance. Also, valuable experience was gained assisting the CCHD during their cryptosporidiosis investigation earlier this year. Most of the elements presented can be implemented with existing resources and expertise available within NDEP.


The NDEP, together with the more than 30 surface water suppliers in Nevada, have agreed that educating the public, including the immunocompromised, regarding issues on Cryptosporidium in water supplies is a positive public health response. Based upon the DOH's experience in Clark County and observation of the national news media, educating the public is a critical element of the public health response to Cryptosporidium. It is appropriate to educate the public that we may not necessarily have all the answers but with current knowledge, are doing all we can to prevent problems. Public education will be an on-going program and may be repeated annually or bi-annually as determined by the DOH and NDEP.

The initial public education information on Cryptosporidium and cryptosporidiosis was produced by the PWS, unless the PWS choose to have NDEP prepare the educational material on their behalf. The public education information is general in nature and contains at a minimum the following information; definition of Cryptosporidium, health effects, transmission, sensitive subpopulations, alternative water supplies, and water system information to include information on treatment practices, compliance with regulations, and monitoring.

The public education material also contains a list of phone numbers including the water system phone number, local county health department phone number, and NDEP phone number. Before distribution, the public education information was reviewed by the DOH and the respective county health departments. The initial public education initiative was coordinated to take place on or around National Drinking Water Week (May 7-13). A more comprehensive document, What is Currently Known About Cryptosporidium, was prepared by the DOH and distributed to the water systems. This document aided water systems, especially the smaller water systems, in answering any questions from their customers. This document was also distributed to individuals that desired more comprehensive information on Cryptosporidium.

The public education material should have reached every customer in Nevada receiving surface water or ground water under the influence of surface water as their drinking water source. Therefore, it is expected that all of the high risk subgroups received the material. The public education material mailed out by the PWSs contained suggestions for alternative water supplies for immunocompromised individuals, along with the State Health Officer's recommendation that severely immunocompromised individuals boil water used for drinking. Also, the CCHD and the WCHD have been working with the local AIDS groups and physicians to further educate them regarding Cryptosporidium.

The DOH also notified the Nevada Child and Family Services Division and the Nevada Bureau of Licensure and Certification regarding this issue. These state agencies permit day care facilities and elder care facilities within the state.

The DOH issued a state-wide press release during the week of May 1 regarding this issue. The US EPA and the national Centers for Disease Control and Intervention issued guidance for people with severely weakened immune systems in July, 1995.


Water System Monitoring — There is currently no federal requirement for PWSs to monitor for Cryptosporidium. The DOH and now the NDEP is requiring several surface water systems to routinely monitor for Cryptosporidium in their source and/or treated water since 1990. These include 8 Lake Tahoe systems seeking waivers to filtration. The two largest PWSs in Nevada, Sierra Pacific and the Southern Nevada Water System (SNWS) have also been monitoring for Cryptosporidium. The DOH required increased monitoring at both the SNWS and within the distribution system of the Las Vegas Valley Water District in response to the outbreak of cryptosporidiosis in Clark County in the first quarter of 1994. At least 4 other PWSs, the City of Henderson, Carson City, National Park Service Lake Mead, and Laughlin will be required to begin monitoring for Cryptosporidium if/when the ICR is finally promulgated.

Due to the unreliability of testing and analytical procedures, it is not recommended that public water systems other than those which are already testing or will be required to test do so on a routine basis. Testing may be required on a case by case basis if deemed necessary by NDEP.

Reporting — The results of all Cryptosporidium tests are reported to the BHPS and WCHD (for Washoe County surface water systems) by the PWS along with the monthly monitoring results required by the Nevada Surface Water Treatment Rule (SWTR). Any test indicating a positive result (either presumptive or confirmed) for Cryptosporidium in raw or treated water shall be reported to the BHPS or WCHD by the PWS as soon as possible, but not later than 24 hours after the results are received. Every effort shall be made to have the samples analyzed so that any positive results can be reported during the work week.

BHPS and WCHD assure that surface water systems comply with the minimum requirements of existing monitoring and reporting requirements, i.e., NAC 445, SWTR and Total Coliform Rule. PWSs are encouraged to expedite these reporting requirements where applicable.

Disease Surveillance — Cryptosporidiosis is a reportable disease in Nevada and is tracked by the BDC&I, and the CCHD and WCHD. Communications between the epidemiologist and drinking water program staff is critical. In the DOH the epidemiologist and the drinking water program staff are located within the BDC&I and BHPS respectively. In the CCHD and WCHD they are located within the Community Health and Environmental Health Divisions.

Communications must flow both ways. The epidemiologist would report cryptosporidiosis cases to drinking water staff and drinking water staff would report the findings of Cryptosporidium in PWSs, water quality problems/violations, and water treatment disruptions/violations to the epidemiologist. This shared information would be used to prevent or abate a waterborne outbreak.

It is also recommended that informal communications be established with the medical community and local pharmacies. Medical practitioners would be encouraged to report high incidence of diarrheal diseases even if persons had not been clinically diagnosed with cryptosporidiosis. This was done in Clark County and provided an early warning that there might be a more widespread infection in the community. Pharmacy reports of increased sales of anti-diarrheal medications might also be a mechanism for detecting an increase in diarrheal diseases in some Nevada communities. This surveillance mechanism would probably be more effective in small communities where there are only a handful of pharmacies. However, it might be possible to establish this surveillance mechanism for larger metropolitan areas as well.


The DOH and now NDEP and WCHD (by interlocal agreement for Washoe County surface water systems) are responsible for assuring that surface water systems are in compliance with EPA and State Board of Health requirements. The DOH, BHPS has placed a priority on implementing the Surface Water Treatment Rule (SWTR) to assure that all surface water systems have treatment, personnel, and monitoring in place pursuant to current SWTR requirements. Overall, Nevada's compliance with the SWTR is very good. Even though some surface water treatment systems have not yet been installed, they are moving forward with necessary treatment considering long design and construction times, and cost. These systems include Sierra Pacific which serves Reno/Sparks, Storey County (Virginia City) and 11 PWS at Lake Tahoe. The DOH and WCHD are working closely with these PWSs and expect that all will be in compliance with the SWTR by June 1996. One possible exception may be Jarbidge in Elko County.

The EPA, the AWWA, and other national water works organizations have stressed the goal of continually optimizing surface water treatment plant operations in a manner designed to produce the lowest possible effluent turbidity (< 0.1 NTU). This goal, along with stringent watershed protection, are the best available methods for reducing the risk of passing Cryptosporidium oocysts into the distribution system. The DOH believes that surface water systems which strive to reach these optimization goals will greatly minimize the risk of exposure to pathogens such as Cryptosporidium in the drinking water delivered to their customers.

The EPA and AWWA are stressing the importance of optimizing filtration on a 24 hour per day basis. The DOH is also stressing the importance of optimized treatment and is encouraging PWSs to meet water quality goals, including turbidity, instead of just complying with the minimum requirements.

The following management and operational guidelines should be followed to achieve optimized treatment:

  • Endorsing the idea that a properly designed and operated plant will be able to consistently produce an effluent turbidity of 0.1 NTU. This includes optimization of all plant unit processes to maximize turbidity removal.
  • Monitoring all plant unit processes closely and responding immediately to any indication of a unit process faltering. The proper operation of all unit processes, including pretreatment processes, is critical to achieving turbidity goals.
  • Operating unit processes at hydraulic loading rates that will enable optimization goals to be met.
  • Establishing procedures for optimizing coagulation, flocculation, and sedimentation unit processes. This includes adjusting coagulant dosages when raw water conditions change. It is important to use jar testing or particle counting to determine proper pretreatment chemical dose.
  • Expanding monitoring of plant operations including continuous turbidity monitoring of individual filters. The DOH strongly recommends the use of particle counters to aid in optimizing the filtration process. This includes use for determining when to backwash a filter, the length of filter-to-waste period, and overall effluent water quality. Particle counters are also valuable when used to track individual filter performance.
  • Calibrating monitoring equipment frequently, including turbidimeters, particle counters, streaming current detectors, and other water treatment monitoring equipment.
  • Establishing procedures for optimizing filter operations to avoid turbidity spikes after service interruptions. This can be achieved by filter-to-waste, by bringing filters on-line slowly, or by the proper use of filter aid chemicals during the backwash process. Turbidity levels or particle count levels should be established for determining when to bring a filter back into service.
  • Operating filters to avoid sudden increases in flow through a filter which could cause particulate breakthrough.
  • Optimizing the performance of backwash recovery systems. Backwash water can contain high levels of pathogens which were concentrated during filtration. Treatment of reclaimed backwash water should be considered to reduce the turbidity. Recycling of backwash water should not be practiced if it interferes with the optimization of the treatment process.

The ability of a plant to provide optimized treatment under all conditions and at all times is dependent upon the reliability of the system equipment, availability of backup equipment, and alarm systems provided. All plants should be capable of timely replacement or repair of failing equipment.

Important activities that are currently not being done are Comprehensive Performance Evaluations (CPEs). Essentially, a CPE is a detailed and comprehensive approach for optimizing treatment plant performance with existing treatment processes, emphasizing non-structural improvements. The EPA, along with other national organizations, has developed a voluntary water treatment optimization program aimed at encouraging US surface water suppliers to survey their facilities, treatment processes, operating and maintenance procedures, and management oversight practices to identify areas that will enhance the system's potential to prevent the entry of pathogens, such as Cryptosporidium, into the treated water, and to voluntarily implement those actions that are appropriate for the system. Systems involved in this program will be asked to have CPEs performed by a third party on the treatment plant. The DOH supports this program and strongly encourages all eligible surface water suppliers in Nevada to participate in the program.

More information — Safe Drinking Water - Guidance for people with severely weakened immune systems US EPA external link

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