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v Health implications of Distribution System Deficiencies Although it is not the purpose of this report to review the optimum engi- neering design. construction, and operation of distribution systems, it is important to recognize that waterborne diseases may result from inade- quate attention to any of those areas. Outbreaks of acute disease associated with contaminated drinking water are reported to the Centers for Disease Control (CDC) by state health departments or to the Health Effects Research Laboratory of the U.S. Environmental Protection Agency (EPA) by state water supply agen- cies. These reports are made on a voluntary basis. The data are reviewed and summarized annually by representatives from CDC and EPA. In the majority of these reports, the etiologic agent is not identified. However, the clinical and epidemiological evidence suggests that most of these outbreaks are caused by infectious agents. In many investigations of outbreaks of unknown etiology, appropriate laboratory specimens are not collected; in others, sophisticated laboratory procedures required for identification of some potential etiologic agents are not performed. Well-documented cases of acute waterborne disease outbreaks in the United States have implicated bacteria, viruses, and protozoa. Some of the bacteria (e.g., Salnzo'`ella and Shigella) and the protozoa (e.g. Giar- dia lamblia and E''tanzoeba histolytica) can be identified by culture or mi- croscopic examination of stool specimens, respectively. Identification of some other pathogenic bacteria (e.g., Campylobacter fetus subspecies je- juni and Yersi''ia enterocolitica) requires the use of special media or incu- bation conditions that are not available in all laboratories. Identification of enterotoxigenic Escherichia cold and viral causes of acute gastroenteritis 137
138 DRINKING WATER AND HEALTH (e.g., Norwalk-like agents and rotaviruses) requires the use of very sophis- ticated laboratory methodology generally accessible only in a research lab- oratory. DEFINITIONS A waterborne disease outbreak is defined by CDC and EPA as an incident in which (1) two or more persons experience similar illness after consump- tion or external use of water intended for drinking and (2) epidemiological evidence implicates water as the source of illness. A single case of acute chemical poisoning constitutes an outbreak if laboratory studies indicate that the water is contaminated by the suspect chemical. With the excep- tion of acute chemical poisoning' data on single cases of acute disease that might be waterborne are rarely reported to CDC or EPA and are not tabu- lated. Municipal or community systems are public or investor-owned water supplies that serve large or small communities, subdivisions, or trailer parks with at least 15 service connections or 25 year-round residents. Semipublic (noncommunity) water systems are those in institutions, in- dustries, camps, parks, hotels, or service stations that may be used by the general public. Individual (private water) systems are those used by single or several residences or by persons such as backpackers who travel outside populated areas. These definitions correspond to those used in the Safe Drinking Water Act (PL 93-523~. ORIGINS OF WATERBORNE DISEASES Sources of the contamination responsible for the outbreak include un- treated surface water, untreated groundwater, treatment deficiencies (e.g., malfunction of a chlorinator), and deficiencies in the distribution system (e.g., cross-connections). Several well-known outbreaks have been caused by deficiencies in the distribution system. Examples include a large outbreak of amebiasis among guests at two Chicago hotels in 1933 (U.S. Treasury Department, Public Health Service, 1936) and infectious hepatitis in members of a college football team (Morse et al., 1972~. In both outbreaks, potable water was contaminated as a result of a defect in the distribution system. INTERPRETATION OF DATA One must be cognizant of the limitations of the data pertaining to these outbreaks in order to avoid inappropriate interpretation. Since some in
Health Implications of Distribution System Deficiencies 139 vestigations were incomplete or were conducted long after the outbreak, the waterborne transmission hypothesis could not always be proven al- though it was the most logical explanation. It is known that the reports of outbreaks received by the CDC and EPA represent only a fraction of those that occur. but the actual extent of these outbreaks is unknown. The likelihood of an outbreak coming to the atten- tion of health authorities varies considerably from one locale to another depending largely upon consumer awareness. physician interest, and dis- ease surveillance activities of state and local health and environmental agencies. The sequence of events leading to the reporting of an outbreak is summarized in Figure V-l, but this sequence can be interrupted at any stage. Large interstate outbreaks and outbreaks of serious illness are most likely to come to the attention of health authorities. On occasion, initial investigation of a few cases of illness has led to the identification of a large outbreak. For example, investigation of 10 culture-proven cases of Shi- gella infection in a Miami suburb in 1974 led to identification of 1,000 cases of waterborne illness (Weissman et al., 1976~. The number of reported outbreaks of different etiologies may depend REPORTING OF AN OUTBREAK I ngesti on Illness Physician Visit Diagnosis t Report to Health Department 1 I nvestigation i Report to Centers for Disease Control and/or U.S. Environmental Protection Agency FIGURE V-1 Sequence of events leading to the reporting of an outbreak.
140 DRINKING WATER AND HEALTH upon the interest of a particular health department or individual. In addi- tion, a few outbreaks involving very large numbers of persons may vastly alter the relative proportion of cases attributed to various etiologic agents. For these reasons, the existing data should not be used as the basis for drawing firm conclusions about the true incidence of waterborne disease outbreaks or about the relative incidence of waterborne diseases of various etiologies. Nevertheless, these data can be useful in determining the caus- ative agents and water system deficiencies that most frequently result in outbreaks. More intensive surveillance and prompter reporting of suspected out- breaks to public health authorities are needed so that more timely and thorough epidemiological investigations can be conducted. By utilizing re- cent advances in diagnostic laboratory techniques, such investigations will increase knowledge of waterborne pathogens, identify factors responsible for the outbreaks, and provide a better estimate of the true magnitude of this route of disease transmission. OUTBREAKS From 1971 through 1978, 224 outbreaks of waterborne diseases were re- ported. Of these, 33 (lS<Xo), involving 10,010 cases, were attributed to de- ficiencies in distribution systems. Features of these 33 outbreaks are sum- marized in Tables V-1 and V-2. Municipal systems were responsible for a total of 68 outbreaks and 33,473 cases, of which 26 outbreaks and 9,298 cases were attributed to distribution system deficiencies (Table V-3. Thus, municipal systems accounted for 78C7o (26 of 33) of the outbreaks and 93% (9,298 of 10,010) of the cases associated with system defi- ciencies. In contrast, defects in semipublic and individual systems were re- sponsible for less than 5% of the outbreaks and cases (Table Van. The most frequently identified deficiencies were indirect cross-connections, which permitted wastewater or toxic chemicals to gain access to the water system by back-siphonage through hoses or through defects in water pipes during periods of low pressure. These defects accounted for 13 (demo) of the outbreaks involving municipal systems (Table V-41. Direct cross-con- nections between sewerage or wastewater systems and municipal potable water systems accounted for 5 (19%~. The etiology of outbreaks involving defects in municipal distribution systems differed from that of municipal outbreaks attributed to other sources (Table V-51. Outbreaks of chemical etiology were much more likely to be associated with such system defects; 10 (38C7o) of the 26 out- breaks resulting from distribution system deficiencies were caused by a chemical, while only two of the 42 (Woo) outbreaks due to other defi
Health Implications of Distribution System Deficiencies 141 ciencies had a chemical etiology. In contrast, no outbreaks of giardiasis were caused by distribution system deficiencies. The 33 outbreaks attributed to deficiencies in all systems were reported by 23 different states. Pennsylvania reported the most (5 outbreaks or into); however, during this period Pennsylvania also reported 44 (into) of the 191 outbreaks caused by other deficiencies. This observation is con- sistent with the fact that Pennsylvania reports the largest number of out- breaks each year. reflecting that state's great interest in outbreaks of waterborne disease. The number of outbreaks due to distribution system deficiencies by year is depicted in Figure V-2. The number of outbreaks involving municipal systems has remained fairly constant, while the semipublic system out- breaks were only reported in 1976-1978. Sewickley, Pennsylvania During the last 10 days of August 1975, an outbreak of diarrhea! illness occurred in residents of Sewickley. A community survey indicated that ap- proximately 60% of the people who obtained their water from the Sewick- ley municipal system had been ill. The illness occurred much more fre- quently in persons using water from this system than in those using well water or water from another, nearby municipal system. Examination of the water system revealed that no free residual chlorine was detectable at several points in the distribution system on at least one of the days on which transmission occurred. The most likely source of the water contamination was an open holding reservoir, since the fence re- stricting access to it had been broken by falling trees the previous winter. Several soda bottles and golf balls were found in that reservoir, but no specific source of human excrete was identified. Despite extensive bacte- rial and viral laboratory studies, no specific etiologic agent was identified. A heavy growth of algae had been observed where contamination was thought to have occurred in the reservoir, but it is not known if the algae played any role in causing the disease (Lippy and Erb, 1976~. Control measures included covering the reservoir and maintaining adequate chlo- rination of the system. Suffolk County, New York During the last week of March 1976, approximately 37% of the people who attended one of four functions at a large catering establishment de- veloped a diarrhea! illness caused by Saln~o,~ella typhinzurium. Although foodborne transmission was initially suspected, epidemiological investiga- tion suggested that the illness was transmitted by contaminated drinking
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146 DRINKING WATER AND HEALTH TABLE V-3 Proportion of Reported Waterborne Outbreaks and Cases Due to Deficiencies in Distribution System by Type of System, 1971-1978a System Outbreaks Cases Municipal 26/68 (memo) 9,298/33,473 (28%) Semipublic 6/129 (Woo) 710/14,470(55'o) Individual 1/27 (4% ) 2/249 ( 1 To ) TOTAL 33/224 ( 15870 ) 10,010/48,192 (21 (Jo ) a From Center for Disease Control. 1978. water. Further investigation indicated that municipal water used to cool a refrigerator compressor was discharged through a pipe submerged in a clogged sink filled with wastewater containing Salmonella typhimurium. The resulting indirect cross-connection resulted in back-siphonage during a period of high demand caused by the operation of on-site pumps to pres- surize the irrigation system for a nearby golf course. Control measures in- cluded removing the discharge pipe from the sink (Center for Disease Control, 1976~. Chattanooga, Tennessee On March 24, 1976, residents of a three-street area in Chattanooga com- plained that their water turned white and smelled of insecticide. Epidemi- ological investigation identified 13 ill individuals. Extremely high concen TABLE V-4 Nature of Distribution System Deficiency in Reported Outbreaks Involving Municipal Systems, 1971 -1978a Deficiency No. Percentb Indirect cross-connections Direct cross-connections Contamination during construction Leaching of copper from pipes Contamination of open reservoir Unknown TOTAL 13 s 3 1 1 1 26 10 so 9 2 2 4 a From Center for Disease Control, 1978. bNumbers are rounded off. Thus, total is not exactly LOOM.
Health Implications of Distribution System Deficiencies 147 TABLE V-S Etiology of Reported Outbreaks Due to Deficiencies in Municipal Distribution System or to Other Deficiencies, 1971-1978a Outbreaks Due to Deficiencies in Outbreaks Due to Distribution System Other Deficiencies Etiology No. Percent No. Percent Unknown Chemical Bacterial diarrhea (Shigella sonnet Salmonella typhimurium) 0 2 3 so 386 8 7 40 5h 2 9 21 Hepatitis 1 4 4 1O Giardia lamblia O oc 10 24C TOTAL 26 100 42 100 a From Center for Disease Control, 1978. bF~sher's tw~tailed exact test, p = 0.00067. c Fisher's tw~tailed exact test, p = 0.01. "rations of chlordane were identified in the water of and soil surrounding a house in which chlordane had been used on March 24 to exterminate ter- mites. The exact mode in which the municipal water supply in this three- street area was contaminated was not identified. However, the most likely explanation is that back-siphonage of chlordane occurred when the con- centrated chlordane solution was diluted with water from a hose. This could have taken place during a period of low pressure resulting from the breakage of several nearby water mains the previous week by a building contractor. Control measures included replacement of all street pipes in the affected area and flushing of pipes to each house (Center for Disease Control, 1976~. Los Lunas, New Mexico On the morning of November 17, 1978, 34 students at an elementary school developed an acute gastrointestinal illness. Epidemiological inves- tigation indicated that the illness was related to contaminated drinking water from the semipublic supply at the school. Examination of the water system indicated a faulty electrical relay switch in the circuit from the pressure gauge for the storage tanks to the well pump and the fluoridator pump. This malfunction permitted the fluoridator to pump concentrated sodium fluoride solution into the storage tanks without simultaneously
148 DRINKING WATER AND HEALTH 2 1 o 5 4 A 6 3 Lot cr m o 1 CC o UJ o LL m 2 7 6 5 4 3 2 1 o Individual 1 1 1 1 1 1 Semipublic O ~ I I I I ~ Municipal ~~ ~: In GAL 1 1 11 I I T ~ I I I Municioal 1 971 1 972 1 973 1 974 1 975 1 976 1977 1 978 YEAR FIGURE V-2 Reported waterborne outbreaks due to deficien- cies in distribution systems, by type of system and year, 1971- 1978.
Health Implications of Distribution System Deficiencies 149 pumping an appropriate amount of water into the tanks. In addition, a toilet in the bathroom near a hallway drinking fountain continued to run following flushing. The continual flow of water into this building caused by this toilet defect accounted for the concentration of fluoride (275 ma/ liter) in the school's water being higher than that in the water in an adja- cent building (93.5 mg/liter). Control measures included repair of the electrical relay switch and the toilet (Center for Disease Control, 1978~. Pierce County, Washington During the first week of May 1978, approximately 70~o of the students and teachers at a rural elementary school developed an acute gastrointes- tinal illness. Epidemiological investigation suggested that the illness had been acquired by drinking water from the semipublic supply at the school. Serologic studies indicated that the outbreak was caused by a Norwalk- like agent. Further investigation revealed that a pipe had been installed to deliver overflow from the air outlet of a pressure tank to a nearby floor drain. On the day when transmission occurred, turbid foul-smelling water was noted on the floor around the drain. The overflow was caused by a jammed baffle at the point of entry of the drain line into the school septic tank. Control measures included removal of the cross connection and repair of the jammed baffle (Center for Disease Control, 1978~. HEALTH EFFECTS OF CHEMICAL CONTAMINANTS IN DISTRIBUTION SYSTEMS Chemical contaminants that may be introduced into drinking water from the distribution system are listed in Table V-6. The adverse health effects of most of these agents have been reviewed in previous publications of the Safe Drinking Water Committee. For the convenience of the reader of this volume, references are provided to the appropriate Drinking Water and Health volume for each of the agents listed in the table. SUMMARY AND CONCLUSIONS Deficiencies in distribution systems were responsible for 15~o of water- borne disease outbreaks reported from 1971 through 1978. Municipal water systems were more likely than semipublic or individual water systems to be associated with outbreaks related to distribution sys- tem deficiencies; 38~o of the outbreaks and 28~o of the cases involving
150 DRINKING WATER AND HEALTH TABLE V-6 Health Effects of Chemical Contaminants Associated with the Distribution System Contaminant Source References to Discussions of Health Effects in the Drinking Water clued Health Series of ReportsU Lead Zinc C. orroslon 1 :309-31 1 1 :258-260 3:270-271 4:179-183 Corrosion and 1:299-302 1 :315-316 corrosion inhibitors Cadmium Corrosion Iron Copper Nickel Chromium Manganese Phosphates Vinyl chloride Asbestos Inorganic hydrated silicates Polynuclear aro matic hydro carbons and re lated substances Tetrachlorethylene Pipe or tank Corrosion, . . deposition, and resus Corrosion C. orroslon 1 :238-240 3:92-96 3:271 4:1 70- 1 74 3:309-312 pension Corrosion 1 :252-253 1 :308-309 3:312-315 1: 287-288 1 :34S-350 1: 242-246 1 :306-307 3:364-369 Deposition and 1:266-270 resuspension 1:31 1-312 3:334-337 3:277-278 Corrosion inhibitors Plastic pipe Asbestos cement pipe Asbestos cement pipe Pipe or tank ,. . mung 1: 783-787 1: 160- 1 68 1:189 4:255-264 1: 769-780 lining 3: 134-142 a References are cited as volume and page number(s), from this (volume 4) and the first three volumes of Dri,~kir7g Water arid Health (National Academy of Sciences, 1977, 1980a,b), e.g., 1:309-311 refers to pages 309-311 in the first volume (Na- tional Academy of Sciences. 1977).
Health Implications of Distribution System Deficiencies 151 municipal systems were caused by such defects. However, these data must be interpreted with caution since reporting of outbreaks is certainly not complete. That municipal systems were most frequently involved probably reflects both the fact that they have more complex distribution systems re- sulting in greater potential for cross-connections and the fact that out- breaks involving municipal systems are most likely to be recognized and reported. The most common defects were indirect cross-connections, which permitted wastewater or toxic chemicals to gain access to the water system by back-siphonage through hoses or defects in water pipes during periods of low pressure. Less frequent defects included direct cross-con- nections, contamination of the system during construction, leaching of copper from pipes, and contamination of an open reservoir. Outbreaks of chemical etiology involving municipal water systems were especially likely to be caused by distribution system deficiencies. RECOMMENDATIONS · Intensify surveillance, investigation, and reporting of outbreaks of waterborne diseases at the local, state, and federal levels. · Maintain adequate pressure in distribution systems so that back-si- phonage cannot occur. · Develop public education programs that focus on the prevention of indirect cross-connections. · Maintain a chlorine residual throughout the system. REFERENCES Center for Disease Control. 1976. Water Related Disease Outbreaks-Annual Summary. Center for Disease Control, Atlanta, Ga. Center for Disease Control. 1978. Water Related Disease Outbreaks-Annual Summary. Center for Disease Control. Atlanta, Ga. Lippy, E.C., and J. Erb. 1976. Gastrointestinal illness at Seuickley, Pa. J. Am. Water Works Assoc. 68:606-610. Morse, L.J., J.A. Bryan, J.P. Hurley, J.F. Murphy, T.F. O'Brien, and W.E.C. Wacker. 1972. The Holy Cross College football team hepatitis outbreak. J. Am. Med. Assoc. 219: 706-708. Weissman, J.B., G.F. Craun, D.N. Lawrence, R.A. Pollard, M.S. Saslau, and E.J. Ganga rosa. 1976. An epidemic of gastroenteritis traced to a contaminated public hater supply. Am. J. Epidemiol. 103:391-398. U.S. Treasury Department, Public Health Service. 1936. Epidemic Amebic Dysentery. The Chicago Outbreak of 1933. National Institute of Health Bulletin No. 166. U.S. Govern ment Printing Office, Washington, D.C. 187 pp.
