From root@aspensys.com Wed Jun 21 09:09:44 1995 Date: Wed, 21 Jun 1995 12:23:43 +0500 MORBIDITY AND MORTALTIY WEEKLY REPORTS Part 2 of 5 ****************************************** Centers for Disease Control and Prevention June 16, 1995 Vol. 44, No. RR-6 BACKGROUND Cryptosporidium parvum has been recognized as a human pathogen since 1976. During 1976-1982, the disease was reported rarely and occurred predominantly in immunocompromised persons. In 1982, the number of reported cases began to increase as a result of the acquired immunodeficiency syndrome (AIDS) epidemic. Initially, the increase in incidence was limited to immunocompromised persons; however, outbreaks and sporadic infections in immunocompetent persons were identified with the aid of newly developed laboratory diagnostic techniques. Cryptosporidium is a protozoan parasite transmitted by ingestion of oocysts that have been excreted in the feces of infected humans or animals. The infection can be transmitted through person-to-person or animal-to-person contact, ingestion of fecally contaminated water or food, or contact with fecally contaminated environmental surfaces. Several municipal waterborne outbreaks of cryptosporidiosis (1-7), including the 1993 outbreak in Milwaukee, have focused attention and concern on the potential for waterborne transmission. Recent studies indicate that Cryptosporidium oocysts are present in 65%-97% of surface water (i.e., rivers, lakes, and streams) tested throughout the United States (8-10). Because Cryptosporidium is highly resistant to chemical disinfectants used to treat drinking water, physical removal of the parasite from water by filtration is an important component of the municipal water treatment process. However, many cities in the United States do not use filtration as part of their water treatment process, and no current method can guarantee complete removal of oocysts. The risk for transmission can be reduced by water filtration if the filters are properly operated and maintained. In the United States, all outbreaks of waterborne cryptosporidiosis detected from 1984 through 1993 occurred in communities where water utilities met state and federal standards for acceptable drinking water quality, and all surface water supplies implicated in those outbreaks had been filtered. These outbreaks indicate that utility compliance with Environmental Protection Agency (EPA) water treatment standards did not adequately protect against waterborne cryptosporidiosis. The EPA turbidity standards have been strengthened since the Milwaukee outbreak, and the finished (i.e., tap) water in Milwaukee at the time of the outbreak would not have met the new standards. Nevertheless, recent reports of Cryptosporidium oocysts in fully treated (i.e., disinfected and filtered) municipal water that was meeting these new standards indicate small numbers of oocysts breached water treatment filters in 27%-54% of the communities evaluated (11,12). The health risk associated with drinking filtered or unfiltered tap water contami-nated with small numbers of C. parvum oocysts is unknown. Although researchers have recovered small numbers of oocysts from drinking water, current laboratory methods cannot reliably determine if these oocysts are viable or are infectious to humans. Moreover, research has not determined whether a) the number of oocysts usually present in drinking water is sufficient to cause illness in humans, b) immunosuppressed persons are more susceptible to lower doses of oocysts than are immunocompetent persons, or c) strains of C. parvum vary in virulence and infectious dose. The results of a study that used a Cryptosporidium strain derived from calves suggested that the infectious dose of oocysts to healthy human volunteers is small (i.e., a median infectious dose could be as few as 132 oocysts) (13). Other reports based on mathematical modeling algorithms indicate that some persons could become infected with a dose as low as one oocyst (14). EPA has proposed a plan to collect data concerning a) the occurrence of several pathogens and chemicals in water and b) the ability of water treatment plants to remove these substances (15). The EPA Information Collection Rule (ICR) will require utilities in the United States that both obtain water from surface water sources and provide service to >=10,000 persons to test for Cryptosporidium oocysts in source water (and in some cases, finished water) for a period of 12-18 months (Appendix A). Almost all utilities are likely to detect oocysts in their surface source water on some occasions, and 24%-50% of utilities can expect to detect oocysts in their treated water (16). When low levels of oocysts are identified in treated water through testing required by the ICR, public health agencies and other local and state officials could be pressured to issue immediate boil-water advisories* or respond in other ways to the perceived public health threat, regardless of whether such measures are necessary. Local and state health departments and water utilities have expressed concern because current data are insufficient to determine the health risks associated with low-level oocyst contamination of fully treated drinking water. WORKSHOP OBJECTIVES The workshop was held to determine and address the public health concerns associated with waterborne cryptosporidiosis and to assess the potential public health, administrative, and economic implications of the ICR's Cryptosporidium testing component. Each of the more than 300 participants received background information regarding cryptosporidiosis and the ICR. The work groups had the following four specific objectives: - To identify surveillance systems and epidemiologic study designs for assessing the public health importance of low levels of Cryptosporidium oocysts or elevated turbidity in public drinking water. - To provide guidance for public health responses to the detection of Cryptosporidium oocysts in drinking water and to provide methods for notifying the public of potential risks for waterborne transmission. - To identify and examine options for preventing waterborne transmission of Cryptosporidium to immunocompromised persons who use public water supplies. - To evaluate and address a) water sampling methods for identifying Cryptosporidium oocysts, b) interpretation of data derived from these methods, c) the status of alternative methods of sampling, and d) laboratory research priorities. Work Group I. Surveillance Systems and Epidemiologic Study Designs Surveillance Systems Local public health officials should consider developing one or more surveillance systems to establish baseline data on the occurrence of cryptosporidiosis among residents of their community and, where possible, obtain sufficient epidemiologic data to identify potential sources of infection. These baseline indices will be helpful in assessing whether oocysts that are found in drinking water are associated with any increases in the number of Cryptosporidium infections in the community. Such surveillance should be considered by all communities whose water utility provides service to >=100,000 persons and whose water supply is derived from surface water. Although communities with populations of 10,000-99,999 persons will be required by the ICR to monitor their source water for Cryptosporidium, they will not be required to monitor their finished water. Nevertheless, those communities in which the water treatment process does not include filtration or in which the treated water quality indicates filtra-tion does not adequately remove oocysts should also consider surveillance for cryptosporidiosis. No single surveillance strategy can be recommended or would be feasible for all locations; therefore, communities should select a method that meets local needs and is most compatible with existing disease surveillance systems or ongoing special studies. Neither increased incidence of diarrhea nor Cryptosporidium infection in a community establishes water as the cause of infection. Any increased occurrence of either diarrhea or laboratory-confirmed Cryptosporidium infection detected by surveillance requires further epidemiologic investigation to identify the source(s) of infection. This work group suggested the following seven approaches to surveillance, which are presented hierarchically by increasing order of the perceived effort and cost. Make cryptosporidiosis reportable to CDC. Each state or city should report cryptosporidiosis cases to CDCIs National Notifiable Disease Surveillance System. This measure was supported and approved by the Council of State and Territorial Epidemiologists (CSTE) in January 1995. Although such action might not improve diagnosis or reporting of cryptosporidiosis by physicians, it provides legal authority for collecting needed information. This type of surveillance is most likely to reflect the occurrence of cryptosporidiosis in immunocompromised populations because health-care providers are more likely to request that such patients who have diarrhea be tested for Cryptosporidium. Monitor sales of antidiarrheal medications. Local pharmacies often have computerized data bases containing the number of medications sold daily. The development of an information exchange between local pharmacists and state or local public health officials is a cost-effective and timely way to detect increases in diarrheal illness in some communities. In addition, these data bases can provide historical data that can serve as an indicator of baseline sales rates for antidiarrheal medication. Monitor logs maintained by Health Maintenance Organizations (HMOs) and hospitals for complaints of diarrheal illness. HMOs and hospitals have computerized systems for logging telephone calls regarding patient illnesses. Information entered promptly into a computerized data base can effectively monitor both complaints of diarrhea and severity of gastrointestinal disease in a community. These data are particularly useful if the local medical-care facility records zip code numbers for persons who are ill, because waterborne illness associated with inadequate water treatment affects persons residing throughout the water distribution area. Monitor incidence of diarrhea in nursing homes. During outbreak investigations, data from nursing homes have implicated drinking water as the source of community infection. Diarrheal illness rates in residents of nursing homes that use municipal drinking water can be compared with illness rates in residents of other nursing homes in the same community that use a different water source (e.g., well water). Because nursing staff usually record the frequency and characteristics of bowel movements for each resident, such data also can be used for other surveillance purposes. Substantial efforts by the local or state health department might be needed to review and extract the relevant data from patient records, which could differ in format by nursing home. If this measure is employed, health departments also should establish a baseline for the population comprising nursing home residents, which usually experiences more gastrointestinal problems than the general population. Monitor laboratory data for Cryptosporidium. Most laboratories do not look for Cryptosporidium in stool specimens submitted for routine parasitologic examination. To obtain this information, health-care providers usually must request specifically that stool specimens be examined for Cryptosporidium. Because health-care providers who treat patients who have AIDS are more likely to suspect cryptosporidiosis as a diagnosis in such patients who have diarrhea, they are more likely than other health-care providers to request specific testing for Cryptosporidium. Thus, current laboratory-based surveillance for cryptosporidiosis would more likely detect an increased number of Cryptosporidium infections in patients who have AIDS than in immunocompetent patients in the general population. To more accurately determine the occurrence of Cryptosporidium infection in the general population, health-care providers must be aware of the public health importance of obtaining data on the occurrence of cryptosporidiosis, and they should be encouraged to submit stool specimens for persons who have symptoms compatible with the disease and to request Cryptosporidium testing. In addition, the cost of the additional laboratory testing for cryptosporidiosis in immunocompetent patients presents an obstacle, especially because specific therapy will not necessarily be implemented as a result of a confirmed diagnosis. Some HMOs and laboratories might be able to provide computerized reports of all Cryptosporidium diagnoses. However, substantial delays might occur between the completion of the test and the entry of data into a computer. Monitor tap water in selected cities. Intensive surveillance in a sample of six to 10 cities known to have Cryptosporidium oocysts in their finished water can provide a method for assessing how often a temporally related increase in diarrheal illness or Cryptosporidium diagnosis occurs during the first week or first 2 weeks after oocysts are found in drinking water. Health departments and public officials in other cities can use information derived from analysis of the data generated at these sites as a basis for local decision making and for educating the public about the public health risks associated with similar levels of oocyst contamination of their water supplies. Health officials in cities participating in this intensive surveillance would need to implement thorough surveillance techniques for recording diarrheal illness and laboratory-confirmed Cryptosporidium diagnoses, and they should monitor finished water for Cryptosporidium oocysts more frequently than required by the ICR. In addition to identifying small outbreaks, these studies could be used to compare the effectiveness of different surveillance methods (including those described previously) and to identify cases of cryptosporidiosis for possible inclusion in epidemiologic studies that could further define the risks for waterborne cryptosporidiosis. A detailed plan for developing intensive surveillance and funding for such activities should be developed by representatives from CDC, EPA, CSTE, and water utilities.