From root@aspensys.com Wed Jun 21 10:12:49 1995 Date: Wed, 21 Jun 1995 13:26:50 +0500 MORBIDITY AND MORTALITY WEEKLY REPORTS Part 4 of 5 ****************************************** Centers for Disease Control and Prevention June 16, 1995 Vol. 44, No. RR-6 All persons, especially immunocompromised persons, should avoid drinking water directly from lakes or rivers. Because water can be ingested unintentionally, immunocompromised persons should be advised that swimming in lakes, rivers, or public swimming pools also can place them at increased risk for infection. This work group suggested that immunocompromised persons can take the following specific measures to help reduce the risk for waterborne cryptosporidiosis: Boiling Water Before Use During waterborne outbreaks or other situations in which a community boil-water advisory is issued, immunocompromised persons should boil water for 1 minute to eliminate the risk for acquiring cryptosporidiosis. Using submicron, personal-use filters (i.e., home or office types of water filters) or high-quality bottled water also can reduce the risk for transmission. However, boiling water is the most certain method of killing Cryptosporidium oocysts. Using Water Filters Only microstraining filters capable of removing particles 1 mm in size should be used by immunocompromised persons and other persons who choose to use a personal-use filter (i.e., home or office water filters) to reduce the risk for transmission of Cryptosporidium. Filters in this category that provide the greatest certainty of Cryptosporidium removal include those that produce water by reverse osmosis, those labeled according to filter manufacturing industry standards as "Absolute" 1 mm filters, and those labeled as meeting American National Standards Institute (ANSI)/NSF (formerly the National Sanitation Foundation) International standard #53 for "Cyst Removal." ** The "Nominal" 1 mm filter rating is not standardized, and many filters in this category might not reliably remove oocysts. Filters that only employ ultraviolet light, activated carbon, or pentiodide-impregnated resins are not effective against Cryptosporidium. Not all filters advertised as effective against Giardia are effective against Cryptosporidium. Because bacterial overgrowth on filters can be an additional health risk (17) and oocysts are likely to concentrate on the outside of filter cartridges, persons should carefully follow the manufacturer's instructions for filter replacement and use. Immunocompromised patients should either have someone else change the used cartridges or use disposable gloves if they themselves change the cartridges. Using Bottled Water Many brands of bottled water adequately reduce the risk for cryptosporidiosis and, thus, provide a reasonable alternative to boiling tap water. However, labeling of bottled water is not standardized with regard to the manufacturing practices used to test for and remove or kill Cryptosporidium oocysts. The origin, microbial flora, and treatment of water before it is bottled vary considerably between bottled water companies and between brands of water produced by the same company. Label information on bottled water often does not provide the consumer with the information needed to identify the lowest-risk product. In general, bottled water obtained from underground sources (i.e., springs or wells) is less likely to be contaminated with Cryptosporidium oocysts than bottled municipal water derived from rivers or lakes. Water from underground sources is unlikely to contain oocysts if it is protected from possible contamination that results from intermittent mixing with surface water and it has been consistently free of coliform bacteria when tested. Because the water bottling industry neither uses a labeling standard for bottled water that reflects the degree of well or spring protection from contaminants nor lists results of coliform testing at the source, consumers might have to seek this information directly from company representatives. Persons who use bottled water as an alternative to tap water that has been boiled must carefully research and choose their supplier. The absence of coliform bacteria in municipal tap water, in tap water treated with submicron filters, or in finished bottled water does not guarantee that the water came from an uncontaminated source (i.e., water negative for Cryptosporidium oocysts) or that it has been treated adequately to remove oocysts. Treating water before bottling by distillation or reverse osmosis filtration, regardless of the source (e.g., well, spring, and municipal tap water), ensures removal of oocysts if they are present. Similarly, water that has been passaged through an "Absolute" 1 mm or smaller filter or through a filter labeled as meeting ANSI/NSF International standard #53 for "Cyst Removal" before bottling will provide almost the same level of oocyst removal. However, bottlers using "Nominal" 1 mm filters as the only Cryptosporidium treatment barrier might not reliably remove oocysts. Use of the word "Microfiltration" on the label does not ensure that filters are effective against Cryptosporidium. Although ozonation of water can kill Cryptosporidium oocysts in experimental conditions, research has not established the appropriate concentration and contact time that are effective against oocysts in bottled water. Municipal tap water that is bottled after treatment with charcoal to remove the chlorine taste or after short-term exposure to ultraviolet light offers no additional protection against Cryptosporidium. Determining Risk for Cryptosporidiosis in Nonoutbreak Settings The magnitude of risk for acquiring cryptosporidiosis from drinking water in a nonoutbreak setting is uncertain and can vary considerably by city depending on the quality of the water source used by utilities and on the quality of water treatment. Current data are inadequate to make a general recommendation that immunocom-promised persons in the United States boil or avoid drinking tap water in nonoutbreak settings. However, immunocompromised persons should be advised that the risk for waterborne transmission is possible and that they can choose to reduce their risk for waterborne cryptosporidiosis by using precautions similar to those recommended during outbreaks. Immunocompromised persons should consult their health-care provider before making such a decision. Immunocompromised persons and other persons who choose to use a personal-use filter or bottled water during an outbreak or nonoutbreak situation should be aware of the difficulties in selecting the appropriate product, the lack of enforceable standards related to oocyst destruction or removal, the cost, and the lifestyle changes that are necessary to consistently use these products for all water consumed. Preliminary data from outbreak investigations indicate that persons who did not consistently use bottled water or filters were as likely to become ill as those who did not use such products (CDC, unpublished data). In a nonoutbreak setting and during periods when finished water quality is within EPA standards, no single indicator of municipal water quality (e.g., minor fluctuations in turbidity, particle size counts, or discovery of low numbers of oocysts) is considered sufficient for issuing or rescinding a boil-water advisory for immunocompromised persons. (See discussion on boil-water advisories, Work Group II. Public Health Responses.) Work Group IV: Water Sampling Methods and Interpretation of Results The ICR and related immunofluorescence methods for detecting Cryptosporidium oocysts in source and finished drinking water are subject to limitations that affect the interpretation of the results. This work group assessed several of these limitations, including the following: Labor Required The ICR techniques are labor intensive and require a lengthy processing time; furthermore, their use requires expertise in microscopy and parasitology. Thus, the tests are costly and depend on the degree of quality control of the laboratory. Distinguishing Characteristics of Infectiousness The assays do not effectively differentiate viable (infectious) or viable (but noninfectious) oocysts from nonviable oocysts. Species Identification All isolates of C. parvum submitted thus far to participating laboratories for testing have yielded positive results using the ICR standard assay. However, oocysts of other species have also been detected with this assay, including Cryptosporidium wrairi (guinea pig), Cryptosporidium meleagridis (turkey), and an unnamed species that affects quail. Some isolates of Cryptosporidium muris (cattle) react to the reagent, whereas isolates of Cryptosporidium baileyi (chicken) do not react (18; CDC, unpublished data). If C. muris and C. baileyi isolates that do react with the reagent are present in a sample, they can be differentiated from C. parvum by oocyst morphology and size. Depending on microscopic image quality and analyst expertise, C. parvum oocysts might be difficult to distinguish from the larger C. baileyi oocysts. Although the assay reagents show adequate specificity for Cryptosporidium, nonspecific reactions or cross-reactions with algae or other particles have been observed. Although a positive result indicates the potential presence of Cryptosporidium oocysts, these oocysts might not be infectious to humans. For these reasons, Cryptosporidium testing results cannot be the only criterion considered when making public health decisions. Other measures that should be considered when assessing public health risk include treatment plant efficiency and water quality data, epidemiologic information, surveillance information, and previous occurrence data. Strain (i.e., virulence) differences between C. parvum isolates cannot be assessed by current identification methods. Recovery Efficiency The ICR methods have an erratic recovery efficiency; therefore, low levels of oocysts in water might not be recovered and the results of oocyst counts for the same specimen could vary. Recovery efficiency and sensitivity are influenced by the charac-teristics of the water sample (e.g., reduced by highly turbid source water or water with high algal content). Water-sample volume and level of analyst or laboratory expertise also affect recovery efficiency and sensitivity. Consequently, water contaminated with C. parvum could yield negative test results. Level of Technical Expertise Required The level of laboratory expertise is particularly critical. EPA has sponsored a preliminary assessment of commercial laboratory proficiency using the immunofluorescence method for low turbidity waters that has been proposed by the American Society for Testing and Materials (ASTM) (19). This assessment has demonstrated substantial laboratory-to-laboratory variability in the identification and reporting of C. parvum oocysts and G. lamblia cysts from experimentally contaminated (i.e., "spiked") test samples. C. parvum oocyst recovery efficiencies ranged from 1.3% through 5.5% (average: 2.8 %). False-negative (55%) and false-positive (18%) results also were reported. However, not all laboratories uniformly applied the ASTM assay during this assessment (i.e., several laboratories had modified this assay). Use of Standardized Techniques Studies that evaluated tap or raw water sediments spiked with C. parvum oocysts have reported oocyst recoveries of 42.0%-89.9% (10,20). Efforts to compare the re-sults of these and other studies have been complicated by the use of slightly different methodologies. Nevertheless, reported recovery efficiencies for spiked samples varied fivefold to fiftyfold, and the results from raw source water or finished drinking water samples will probably be as variable. The decision to implement the Cryptosporidium-specific portion of the ICR will be made partially on the basis of the results of a planned performance evaluation trial with the ICR method. Need for Alternative Methodologies Alternative methods or modifications to existing methods have been reported or are being developed. None of these alternatives currently supplant or improve the current ASTM or ICR methods, and research needs to continue on the development of alternative methodologies. Such methodologies are needed to better meet public health objectives for assessing the health significance of oocysts in drinking water, and they should enable water treatment operators to test and react to the presence of oocysts in source or finished water within hours. WORK GROUP CONCLUSIONS These work group conclusions are the summarized suggestions from the proceedings of each work group, as presented by the work group leaders at the concluding plenary session of the workshop, and they were drafted with multiple opportunities for open input from all participants. The workshop formalized the awareness that current knowledge of Cryptosporidium, particularly waterborne cryptosporidiosis, is minimal. This level of knowledge does not provide a scientifically sound basis for many essential decisions regarding the public health risks associated with the infection. This report provides, on the basis of available information, potential strategies for managing cryptosporidiosis. Moreover, these discussions assist with focusing researchers on possible ways to attain the information needed to better understand the risk factors associated with waterborne cryptosporidiosis, thereby enhancing the eventual development of effective prevention strategies. Surveillance Systems and Epidemiologic Study Designs Local, state, and national public health agencies should cooperatively initiate and develop surveillance and epidemiologic investigations to assess the public health significance of low levels of Cryptosporidium oocysts in public drinking water. Public Health Responses Discovering Cryptosporidium oocysts in low levels in finished water should not be the only reason for issuing a boil-water advisory. Additional support for such an advisory should include other data indicating that the water quality is unacceptable. A task force should be created to develop general guidelines for implementing and lifting boil-water advisories and to assist local agencies in deciding when boil-water advisories are necessary. A coordinated local-to-national effort should be made before implementation of the ICR to provide information concerning Cryptosporidium and drinking water to public health officials, water utility officials, health-care providers, immunosuppressed populations, and the general public. Such information should include appropriate prevention strategies. Cryptosporidiosis in Immunocompromised Persons A coalition or task force should be established that will place high priority on educating immunocompromised persons about cryptosporidiosis because of the increased risk for severe disease if they become infected. This group should provide information to immunocompromised persons that explains how to reduce the risk for cryptosporidiosis, regardless of the source of transmission, and about specific meas-ures they can take to further reduce the risk for waterborne transmission. Water Sampling Methods and Interpretation of Results Current methods are limited with regard to detecting oocysts in source and finished drinking water. These technical limitations restrict the ability of public health officials to practically interpret data on the occurrence and public health importance of Cryptosporidium in drinking water. Research should be accelerated to develop alternative, dependable methods for detecting Cryptosporidium in drinking water.