Drinking Water and Health, Volume 1 (1977) / Chapter Skim
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III MICROBIOLOGY OF DRINKING WATER
III MICROBIOLOGY OF DRINKING WATER
Pages 63-134
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From page 63... ...
Microbiological contaminants, such as fungi and algae, do not seem to be important causes of waterborne disease, although they are sometimes associated with undesirable tastes and odors. EPIDEMIOLOGY The average annual number of waterborne-disease outbreaks in the United States reported since 1938 is shown in Figure III-1 (Center for Disease Control, 1976b)
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From page 64... ...
Four typhoid fever outbreaks affected 222 people and involved semipublic and individual water systems. In 1974, 28 waterborne-disease outbreaks, comprising 8,413 cases, were reported to the Center for Disease Control (1976a)
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From page 65... ...
(1976) have drawn attention to the large number of waterborne disease outbreaks involving travelers.
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From page 66... ...
Seventeen of the 24 outbreaks and about 9070 of the cases reported to CDC were designated as "acute gastrointestinal illness." This category includes cases characterized by gastrointestinal symptoms for which no specific etiologic agent was identified. Cases resulting from water treatment deficiencies (2,695)
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From page 67... ...
Some enteric pathogens are highly virulent, causing infection when relatively few cells are administered (e.g., Shigellaflexneri and S dysenteriae)
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From page 68... ...
Infants and the aged may be particularly susceptible. Previous exposure to a given pathogen is important, in that coproantibodies may prevent infection with a strain that is generally present in the population, whereas a new serotype introduced into the water supply may present an increased hazard.
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From page 69... ...
However, enteric pathogens may survive much longer times in lake or river sediment than in free waters, and resuspension of such pathogen-loaded sediments at a later time may introduce a "slug" of bacteria into the waters that is not completely removed by treatment systems. Estimation of Disease Potential by Direct Quantitation of Bacterial Pathogens The detection of bacterial pathogens in water polluted with human or animal fecal matter is relatively easy when large numbers of organisms are present (American Public Health Association, 1975~.
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From page 70... ...
A recent review appeared in the fourteenth edition of Standard Methods (American Public Health Association, 1975~. There are serious limitations to the use of direct isolation of specific pathogenic bacteria for evaluating water quality.
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From page 71... ...
cold ferments lactose with the formation of acid and gas; Salmonella and Shigella do not ferment lactose. One source of confusion is the necessity to distinguish between E
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From page 72... ...
The "coliform group," as defined in Standard Methods (American Public Health Association, 1975) , comprises all "aerobic and facultative anaerobic, gram-negative, nonspore-forming, rod-shaped bacteria which ferment lactose with gas formation within 48 hr at 35 C." This is not a taxonomic grouping, but an operational one that is useful in water-supply and sewage-treatment practice.
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From page 73... ...
Little information exists on the survival of bacteria in finished water, and the data on other types of water are scattered and fragmentary. McFeters et al.
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From page 74... ...
In the final analysis, testing for coliform, while not perfect bacteriologically, is still the most reliable indicator of the possible presence of fecal contamination and therefore of the pathogens that may be present in water. OTHER INDICATOR ORGANISMS Because of certain limitations of the coliform group as general indicators of water quality, workers have continually searched for better indicator organisms.
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From page 75... ...
It would be undesirable and extremely risky to substitute any organism for the coliform group now, although research studies that compare other indicator organisms with coliforms are warranted. RAPID METHODS FOR COLIFORM COUNTS There is great need for a rapid method of coliform counts which could give results in a shorter time than the 18-24 h required by the membranefilter method.
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From page 76... ...
It seems unlikely that such a method could ever be made sensitive enough to detect single coliform cells in 100-ml water samples, so that it probably will never replace standard methods, but it might prove useful in process control in large water systems. The EPA at Cincinnati has also developed a 7-h fecal coliform test, employing a membrane filter technique (Reasoner and Geldreich, 1974~.
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From page 77... ...
Donald Maddox, Chief, Water Supply Systems Section, Region V, USEPA (personal communication to Walter Ginsburg) , the subject of sample frequency was again discussed by the Committee that revised the 1962 Drinking Water Standards, and no changes were made.
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From page 78... ...
national standards for bacteriological water quality were established in 1914 (Public Health Reports, 1914~. These standards were specifically applicable to water used on interstate carriers, but were adopted quite early (formally or informally)
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From page 79... ...
Coliform organisms should not be detectable in 100 ml of any two consecutive samples." In nonpiped systems, the coliform count should not exceed 10/100 ml. The European Standards are comparable to the International standards, but do not distinguish-in terms of quality between disinfected and undisinfected water.
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From page 80... ...
Because it is not feasible to assay for bacterial pathogens directly in water, it is important to consider the utility of the coliform test in ensuring the bacteriologic safety of drinking water. A direct approach to assessing the significance of the coliform count would be to obtain e-idence of a correlation between numbers of coliforms and numbers of pathogenic bacteria (e.g., salmonellae or shigellae)
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From page 81... ...
typhosa and coliforms are members of the same group of bacteria and are likely to show similar tolerance and sensitivities to environmental influences. From the data in Figure III-2 and from recorded waterborne outbreaks of typhoid fever, Kehr and Butterfield estimated a minimal infecting dose of S
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From page 82... ...
Assuming equal destruction of typhoid bacteria and coliforms during treatment, if the finished water contained one coliform/100 ml (a reasonable possibili
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From page 83... ...
added much weight to the rationale of establishing a coliform standard for drinking-water sources. His analyses showed that if raw water has fewer than 1,000 coliforms/100 ml, then it would be very likely that the salmonellae in finished water would be below infective levels.
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From page 84... ...
Bacteriological testing or the imposed use of bacteriological standards are adjuncts, not replacements for good-quality raw water, proper water treatment, and integrity of the distribution system. The present coliform standards appear adequate to protect public health when: raw water is obtained from a protected source, is appropriately treated, and is distributed in a contaminationfree system.
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From page 85... ...
Even though water treatment is adequate and chlorine disinfection is provided, quality could deteriorate in the distribution system as a result of growth of organisms other than detectable conforms. Finished water containing flee, or unfiltered turbid waters, may carry organisms past the disinfection treatment, or the organisms may be protected by association with larger forms of life, such as nematodes (Chang et al., 19601.
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From page 86... ...
Rather, the use of a standard plate count limitation will: 1. Provide a method of monitoring for changes in the bacteriological quality of finished water in storage reservoirs and distribution systems.
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From page 87... ...
Epidemiological studies of water quality and health, with application of more sensitive methods for detecting pathogens in drinking water and better reporting of outbreaks of waterborne disease.
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From page 88... ...
Only viruses that can withstand such conditions will remain infectious and thus able to implant further down the digestive tract. The most important human enteric viruses are the enteroviruses (i.e., acid-stable picornaviruses)
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From page 89... ...
Nevertheless, transmission of enteric viruses by water had already been surmised by the time cell cultures became available. History of the Enteric Viruses The first reported epidemic of poliomyelitis in the United States occurred in New England (Putnam and Taylor, 1893~.
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From page 90... ...
suggested that the incidence of waterborne infectious hepatitis is grossly underreported, but estimated that less than 1% of the cases of this disease result from transmission by water. Viruses that are still unidentified may also be responsible for waterborne disease, since there are many episodes of waterborne gastroenteritis and diarrhea of unknown etiology.
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From page 91... ...
Viruses transmitted by a fecaloral cycle can always be transferred directly from person to person, but this requires close contact. Several of the enteric viruses are known to be transmitted by water, but only some of the time.
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From page 92... ...
In water polluted with human feces, the shellfish accumulate enteric viruses (Liu et al., 1967; Metcalf and Stiles, 1965; and Mitchell et al., 1966) , including the hepatitis virus.
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From page 93... ...
There have been two outbreaks of gastroenteritis in the United States (one of which led to hepatitis) in which enteric viruses were recovered from the drinking water.
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From page 94... ...
According to an EPA study of 155 cities that use surface-water supplies, 1 of every 30 gal that enter water-treatment plants has already passed through the wastewater system of a community that is upstream (Culp et al., 1973~. With the increasing use of renovated water, there is a need for methods that can detect the enteric viruses that might occur in raw or finished water.
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From page 95... ...
methods in combination were recommended for isolation of as many enteric viruses as possible (Hatch and Marchetti, 1975~.
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From page 96... ...
as laboratory strains. RECOVERY PROCEDURES FOR VIRUS IN FINISHED WATER There are extensive reviews of methods for recovering waterborne viruses (Hill et al., 1971; Sobsey, 1976~.
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From page 97... ...
Although there is no universal method for concentrating all enteric viruses from water, some methods are quite effective for some of the enteric viruses in some types of water. Flowthrough-filter adsorption-elusion systems and ultrafiltration methods with anisotropic, polymeric membranes in tangential-flow systems are the best for recovery of small quantities of enterovirus in large volumes of treated or finished water.
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From page 98... ...
98 a~ 43 o an · _ ._ so o o _ ~ Cal V, .~ o .~ At: a' so ,4 ._ V, ._ s~ o 2 .
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From page 99... ...
99 c: ~ ~ ~ C ~ ~ ~ l~ ~` 0\ _ ~ ~ ~ ~ ~ , 3 eC - C~ O C-~ - c~ D V~ U~ ~ ~ ~ ~ ~ ~ ~ ~ 1 1 - ~ o r~ 0 r~ ~ oo ~ ~ ~ ~ r~ X ~ 1O - 1 1 o X ~ ', _ _ \o V)
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From page 100... ...
The success of the laboratory trials has led to inclusion of flowthrough procedures in the fourteenth edition of Standard Methods for the Examination of floater and Wastewater (1975) as a tentative method for finished water.
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From page 101... ...
Both the flowthrough method of virus collection and larger-volume coliform tests may have a future as standard methods for discretionary, intensive testing of finished water; neither should be regarded as a routine monitoring method for on-line quality control. Health Effects of Viruses in Drinking Water Large numbers of enteric viruses are present in some human feces and, therefore, in wastewater.
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From page 102... ...
Poliovirus infection by the oral route had to be studied during development of the "live-virus" poliomyelitis vaccines. Sabin found that nonhuman primates could not be substituted for man in such investigations, because of species differences in the relative susceptibility of the intestines to poliovirus infection.
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From page 103... ...
The available data on polioviruses have important limitations; unfortunately, far less information seems to be available concerning infectivity, by the oral route, of other intestinal viruses. The dose of coxsackievirus B5 that would infect 50% of newborn mice to which it was
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From page 104... ...
There is no valid basis for establishing a no-effect concentration for viral contamination of finished drinking water. Virus Removal in Water Treatment When viral disease occurs in association with a drinking-water supply, one first has to consider the possibility that cross-contamination or backsiphonage may have admitted waste water into the distribution system.
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From page 105... ...
indicate that 30 PFU/liter constitutes a "reasonable virus load in moderately polluted water." One would hope to remove or inactivate all viruses before the treated drinking water were considered "finished." Berg (1973) has offered to resolve this difficulty by requiring that reclaimed and other potable water be disinfected so as to destroy at least 12 logarithmic units of a reference virus at 5°C and that the finished water be tested frequently to ensure that there is not more than 1 PFU in a 100-gal (379-liter)
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From page 106... ...
Four recent, extensive studies indicated that virus removal from 90% to well above 99% can be achieved by coagulation and settling under carefully controlled conditions (Foliguet and Doncoeur, 1975; Manwaring et al., 1971; Schaub and Sagik, 1975; and Thorup et al., 1970~. Either aluminum sulfate or ferric chloride proved a good primary floccueant for virus removal.
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From page 107... ...
DISINFECTION If all of the treatments described above were applied sequentially to raw water, one could expect a total of 6 logarithmic units of virus removal or destruction, without recourse to chemical disinfection. However, chemical disinfection seems to be more reliable than the other treatments.
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From page 108... ...
(1971) emphasized differences in resistance among the groups of enteric viruses (as well as the importance of clumping of virus particles)
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From page 109... ...
When the water contains nitrogenous substances, chlorine should be added to the "breakpoint," beyond which any further added chlorine will be free to inactivate viruses (Kruse et al., 1971~. Chlorine dioxide (Cl02)
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From page 110... ...
If the presence of virus in finished water results from undertreatment of virus-contaminated raw water, treatment should be intensified (to include coagulation, settling, filtration, and chemical disinfection, such as breakpoint chlorination, if these are not already being done) , and efforts should be made to alleviate the contamination of raw water.
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From page 111... ...
The results of virological tests on contaminated water are unlikely to be known before human illness occurs. Microbiological indicators may have a limited correlation with viral contamination, but they and chlorination afford more protection to public health than does any available alternative approach to routine monitoring of finished water.
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From page 112... ...
The intestinal helminths will be considered, especially in terms of the characteristics that make then susceptible to elimination from sewage effluents and that also make them unlikely to be found in raw or finished water. Protozoa Parasitic protozoa replicate in the human host, and may be responsible for severe disease.
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From page 113... ...
The well-studied South Bend outbreak in 1953, in which there were at least 750 infections and 30 clinical cases, with 4 fatalities, was due to sewage contamination of a private water supply to a factory (LeMaistre et al., 1956~. One outbreak involved a public system and accounted for 25 cases (Craun and McCabe, 1973~.
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From page 114... ...
Information on this and other Ciardia outbreaks is reported in Foodborne and Waterborne Disease Outbreaks, Annual Summary 1974, Center for Disease Control (1976a)
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From page 115... ...
It is the only one of the cestodes infecting humans that has a direct life cycle; i.e., the egg serves as the infecting agent by the oral route. The larva and adult develop from the egg.
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From page 116... ...
However, they are reported to produce a gummy substance, small quantities of which confer an unpleasant taste to finished water. Besides having this characteristic, the nematodes may pose a problem in that they are resistant to chlorine; free residual chlorine at 2.5-3.0 ppm failed to immobilize them in 120 m (Chang et al., l961~.
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From page 117... ...
It is also important to emphasize the danger of faulty distribution systems, even when relatively high residual-chlorine concentrations are maintained; cross-connection control is essential. Conclusions The principal pathogenic parasites that may escape our sanitary barriers in public water supplies are the protozoa Entamoeba histolytica and Giardia lamblia.
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From page 118... ...
SUMMARY MICROBIOLOGY OF DRINKING WATER The incidence of enteric disease in the United States has been reduced by elective water treatment systems, but in 1974 the Center for Disease Control reported 28 waterborne disease outbreaks and 8,413 cases. In 1975 there were 24 outbreaks and 10,879 cases.
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From page 119... ...
Good engineering and public health practices emphasize the need for using raw water of the highest possible quality. Bacteriological testing, or the imposition of bacteriological standards, are adjuncts to, not substitutes for, good~uality raw water, proper water treatment, and integrity of the distribution system.
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From page 120... ...
are the best indicators available today for routine use in determining the probable levels of viruses in drinking water. The best available water treatment technology, if diligently applied, should provide a high degree of assurance that viruses injurious to human health are absent from finished drinking water.
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From page 121... ...
that can be present in raw water will be controlled in public water supplies by well-regulated flocculation, filtration, and disinfection. Testing One of the greatest deficiencies of customary methods for evaluating the bacteriological quality of water is that results from tests are unknown until after the sampled water has already entered the distribution system and been used.
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From page 122... ...
1943. Influence of pH and temyrature on the survival of coliforms and enteric pathogens when exposed to free chlorine.
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From page 123... ...
1960. Survival and protection against chlorination of human enteric pathogens in free-living nematodes isolated from water supplies.
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From page 124... ...
1976. Waterborne Disease Outbreaks in the U.S.
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From page 125... ...
1968. The significance of numbers ofcoliform bacteria es an indicator of enteric pathogens.
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From page 126... ...
Virus and Water Quality: Occurrence and Control. Proceedings of the Thirteenth Water Quality Conference, vol.
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From page 127... ...
1958. The effect of chlorine in water on enteric viruses.
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From page 128... ...
1971. Relative resistance of twenty human enteric viruses to free chlorine in Potomac water.
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From page 129... ...
1965. The accumulation of enteric viruses by the oyster, Crassostrea virginica.
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From page 130... ...
1967. Minimal infective doses of viruses for man by the oral route.
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From page 131... ...
Proc. AWWA Water Quality Technology Conference, Dallas, Texas, pp.
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From page 132... ...
159-169. Proceedings of the Thirteenth Water Quality Conference, University of Illinois Bulletin, Urbana.
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From page 133... ...
1943. Relative resistance of coliform organisms and certain enteric pathogens to excess lime treatment.
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From page 134... ...
1972. The coliform count as a measure of water quality In R
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