B Microbial Pathogens in Coastal Waters

Bacterial diseases associated with polluted recreational waters and shellfish have been documented for over 100 years. Typhoid, for example, was first documented in association with recreational waters as early as 1888 (Craun 1986). Transmission of viral disease via recreational exposure to sewage contaminated waters was first documented as early as the 1950s, and is now well established (Stevenson 1953, Balarajan et al. 1991, Alexander et al. 1992, Fewtrell et al. 1992). Transmission of typhoid and cholera associated with the consumption of contaminated seafood has long been recognized, and by 1956 the risk of viral diseases, specifically hepatitis, was documented (Roos 1956). Disease occurs through two pathways of exposure: swimming in contaminated waters or eating contaminated fish or shellfish. Bathing in contaminated water can result in accidental swallowing or aspiration of infective pathogens. Ingestion of contaminated seafood can cause infection by pathogens or toxicity from toxins elaborated by microorganisms or algae. The effects of microbial infections can range from infection without overt disease to acute, self-limited respiratory, skin, gastrointestinal, and ear infections to extreme gastrointestinal and liver disorders and even to death.

MICROBIOLOGIC AGENTS ASSOCIATED WITH WASTEWATER

Over 100 different enteric pathogens may be found in sewage. These includes viruses, parasites, and bacteria, all of which may be associated with waterborne disease.



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Managing Wastewater in Coastal Urban Areas B Microbial Pathogens in Coastal Waters Bacterial diseases associated with polluted recreational waters and shellfish have been documented for over 100 years. Typhoid, for example, was first documented in association with recreational waters as early as 1888 (Craun 1986). Transmission of viral disease via recreational exposure to sewage contaminated waters was first documented as early as the 1950s, and is now well established (Stevenson 1953, Balarajan et al. 1991, Alexander et al. 1992, Fewtrell et al. 1992). Transmission of typhoid and cholera associated with the consumption of contaminated seafood has long been recognized, and by 1956 the risk of viral diseases, specifically hepatitis, was documented (Roos 1956). Disease occurs through two pathways of exposure: swimming in contaminated waters or eating contaminated fish or shellfish. Bathing in contaminated water can result in accidental swallowing or aspiration of infective pathogens. Ingestion of contaminated seafood can cause infection by pathogens or toxicity from toxins elaborated by microorganisms or algae. The effects of microbial infections can range from infection without overt disease to acute, self-limited respiratory, skin, gastrointestinal, and ear infections to extreme gastrointestinal and liver disorders and even to death. MICROBIOLOGIC AGENTS ASSOCIATED WITH WASTEWATER Over 100 different enteric pathogens may be found in sewage. These includes viruses, parasites, and bacteria, all of which may be associated with waterborne disease.

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Managing Wastewater in Coastal Urban Areas Viruses Enteric viruses are obligate human pathogens. That is, they replicate only when within the human host. Their structures may allow prolonged survival outside the human body, in the environment. There are over 120 enteric viruses that may be found in sewage. Table B.1 lists some of the better described viruses, including the enteroviruses (polio-, echo-, and coxasackieviruses), hepatitis A virus, rotavirus, and Norwalk virus, and the annual incidence of disease and case mortality rates for all sources of exposure (Bennett et al. 1987). Virus numbers reported in sewage vary greatly and reflect the variation in infection in the population excreting the agent, the season of the year (outbreaks of viral disease are often seasonal), and methods used for their recovery and detection. Table B. shows virus numbers that have been reported in sewage. Treatment reduces but does not eliminate viral contamination (Melnick and Gerba 1980, Rose and Gerba 1990, Asano et al. 1992). Over 100 outbreaks of hepatitis and viral gastroenteritis have been associated with the consumption of sewage contaminated shellfish in the United States (Richards 1985). The reported outbreaks have increased from less than 10 in the years 1966-1970 to more than 50 in the years 1981-1985. Although this apparent increase could be due to reporting artifacts, the number reported most certainly represents a great underestimate because of the long incubation period for hepatitis A and the difficulty in tracing the source. From 1983-1989, the incidence of hepatitis A increased 58 percent with 14.5 cases in 100,000 in the United States. An estimated 10 percent of these cases may be due to foodborne transmission, including shellfish (CDC 1990). Viral outbreaks due to recreational exposure to contaminated waters have been documented in the United States. Between the years 1986 and 1988, 41 percent of these were an undefined gastroenteritis and likely of a viral etiology (CDC 1990). Shigella and Giardia were also predominant causes of recreational outbreaks of disease. Viruses (entero- and rotaviruses) have been isolated from recreational waters in the absence of any discharge from a wastewater treatment plant (Rose et al. 1987). Parasites The parasites of primary public health concern for wastewater exposure are the protozoa and helminths. The helminths include roundworms (Ascaris), hookworms, tapeworms, and whipworms. These organisms are endemic in areas where there is inadequate hygiene and their transmission is generally associated with untreated sewage, untreated sludges, and night soil, with very little documentation of waterborne transmission.

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Managing Wastewater in Coastal Urban Areas TABLE B.1 Characteristics of Enteric Viruses (Bennett et al. 1987) Virus Group 1985 Reported Cases Mortality Rates (%) Levels in Sewage/L Diseases Enterovirus: Poliovirus 6,000,000 7 0.001 10 182-92,000 Paralysis Aseptic meningitis Coxasackievirus A       Herpangina Aseptic meningitis Respiratory illness B       Paralysis fever Pleurodynia Aseptic meningitis Pericarditis Myocarditis Congenial heart anomalies Nephritis Echovirus:       Respiratory infection Aseptic meningitis Diarrhea Pericarditis Myocarditis fever, rash Hepatitis A  Virus 48,000 0.6 5101 Infectious hepatitis Reovirus     1-1,247 Respiratory disease Gastroenteritis Adenovirus 10,000,000 0.01 100-100,000 Acute conjunctivitis Diarrhea Respiratory illness Eye infection Rotavirus 8,000,000 0.01 401 Infantile gastroenteritis Norwalk agent (probably a calcivirus) 6,000,000 0.0001   Gastroenteritis Astrovirus       Gastroenteritis Calcivirus       Gastroenteritis Snow Mt. Agent (probably a calcivirus)       Gastroenteritis Norwalk-like virus       Gastroenteritis Non-A, Non-B Hepatitis 50,000 0.4   Hepatitis

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Managing Wastewater in Coastal Urban Areas The pathogenic enteric protozoa Giardia lanmblia, Cryptosporidiumn, and Entamnoeba histolytica are listed in Table B.2. These enteric protozoa are important waterborne pathogens and are a cause of acute and chronic diarrhea. They replicate only within their host. The cyst or oocyst that is excreted in the feces is the infective form, able to survive in the environment and 10 to 1,000 times more resistant to water disinfection than the bacteria (Jarroll 1988, Korick et al. 1990). Filtration is a more effective means of removal. Ingestion of small numbers of cysts (between 1 and 10) are capable of initiating an infection (Rose et al. 1991a). Therefore, as for viruses, low levels are of greater public health concern than low levels of bacterial contamination. Entanioeha histolvtica infects only humans. Waterborne transmission is usually from raw sewage contamination of the water. Although only one TABLE B.2 Characterization of Pathogenic Protozoa in Relationship to Waterborne Diseases   Giardia Cryptosporidium Entamoeba Isospora Type of Protozoan Obligate enteric amoebae Obligate enteric coccidian Obligate enteric amoebae Obligate enteric coccidian Transmission Routes Fecal-oral by cysts Fecal-oral by oocysts Fecal-oral by cysts Fecal-oral by oocysts Reservoirs of Infection for Man Infected animals and man, Chronic human carriers Infected animals and man, Chronic human carriers Infected animals and man, Chronic human carriers Infected animals and man, Chronic human carriers Documented Waterborne Disease in the U.S. 106 outbreaks 1965-1988 >26,010 cases 3 outbreaks 1980-1988 > 13,1 17 cases 8 outbreaks1 1920-1988 1,495 cases None Type of Illness Acute (5-30d.) and chronic (months) infections of diarrhea Self-limiting diarrhea, Cholera-like 7-10 day Diarrhea, Liver abscesses, Mortality 0.026% Diarrhea Levels in Sewage 530-100,000/L 10-1,000/L 28-52/L Unknown 1 Only 1 since 1971.

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Managing Wastewater in Coastal Urban Areas waterborne outbreak has been documented since 1971 in the United States (Craun 1991), this organism is an important cause of morbidity worldwide. Giardia lamblia is the most common protozoan infection in the United States and is a major public health concern. Of an estimated 60,000 cases of illness due to Giardia (giardiasis) per year, it has been suggested that 60 percent of these are waterborne (Bennett et al. 1987). There has been an increase in the reported incidence of waterborne giardiasis since 1971 (Craun 1991). Because of animal reservoirs, the role sewage contamination has played in this increase has been impossible to determine. Giardia cysts have been detected in treated and untreated sewage at levels between 530 and 100,000/liter (Sykora et al. 1990). Cryptosporidium was first recognized as a waterborne agent in 1985 (D'Antonio et al. 1985). Cryptosporidiosis is a serious and potentially fatal infection in the immunocompromised (infants less than six months of age, the elderly, and those with disease states that impair the immune system) and may be more prevalent in children under one year of age. In the United States, Cryptosporidiunz appears to account for between 0. 1 and 1.9 percent of the incidences of acute diarrhea (CDC 1990). Yet sporadic outbreaks associated with drinking water have occurred in which 13,000 people became ill (Hayes et al. 1989) as have outbreaks from recreational exposure to water in lakes (Gallagher et al. 1989). Occurrence in treated wastewater effluents has been documented and the levels appear to be slightly less than Giardia (Rose et al. 1988). Bacteria Enteric bacterial pathogens remain an important cause of disease in the United States (Table B.3). Classical waterborne bacterial diseases such as dysentery, typhoid, and cholera, while still very important worldwide, have dramatically decreased in the United States since the 1920s (Craun 1991). However, Campylobacter, non-typhoid Salmonella, and pathogenic Escherichia coli have been estimated to cause 3 million waterborne illnesses per year (Bennett et al. 1987). Foodborne cases represent a much greater percentage. The specific role of polluted coastal waters in the acquisition of these infections has been difficult to determine. While the previous bacteria all have nonmarine animal reservoirs, the noncholera Vibrio sp. may be found naturally in the marine environment and contributes to a portion of the 50,000 cases of seafood-associated gastroenteritis annually reported in the United States. No animal reservoirs have been identified for Shigella; therefore humans appear to be the only source. This agent was responsible for the majority (52 percent) of recreational waterborne outbreaks between 1981 and 1987 in lakes and rivers for a total of 428 cases of shigella gastroenteritis

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Managing Wastewater in Coastal Urban Areas TABLE B.3 Characterization of Enteric Bacterial Pathogens (Feachem et al. 1983, Bennett et al. 1987) Bacteria Reported Cases in the U.S. Percent Waterborne Mortality Rates (%) Levels in Sewage/100ml Campylobacter 8,400,000 15 0.1 NR1 Pathogenic E. coli 2,000,000 75 0.2 NR Salmonella 10,000,000 3 0.1 2.3 - 8,000 S. typhi 600 10 6 NR Shigella 666,667 10 0.2 1 - 1,000 Vibrio cholera 25 NR I NR Vibro non-cholera 50,000 10 4 10 - 10,000 Yersinia 5,025 35 0.05 NR 1 NR = Not reported. (shigellosis). The source of the contamination was never fully described in these outbreaks. Like the enteric viruses, the overuse of recreational sites may lead to the contamination, degradation of water quality, and disease outbreaks (CDC 1990). Recreational outbreaks in marine waters have not been as well documented. Intestinal bacteria have been used for more than 100 years as indicators of the presence of feces in water and overall microbial water quality. These indicator bacteria live in the intestinal tract of humans and other warm-blooded animals without causing disease. They are naturally excreted in feces in large numbers (109 to 1010 per gram of feces). Commonly measured are total coliforms and a subset of this group, the fecal coliforms, which are considered to be more predictive of fecal contamination. Generally greater than 90 percent of the coliforms found in feces of warm blooded animals are a specific fecal coliform Escherichia coli (E. coli). In addition to the coliform bacteria, fecal streptococci and enterococci have been used to monitor water quality and are also natural flora of the intestines of animals, including humans. The use of bacterial indicators is discussed in Chapter 4. Animal and Wildlife Sources Domesticated animals and wildlife may excrete pathogenic microorganisms that are infectious to humans. Agricultural runoff, stormwaters, and direct input from animals leads to the contamination of waterways, which eventually discharge to coastal areas. There is no evidence at this time that animal enteric viruses infect humans. Two of the enteric protozoa carried by animals, Giardia and Cryptosporidium,

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Managing Wastewater in Coastal Urban Areas may be pathogens of concern in nonpoint sources. Giardia is found in 90 percent to 100 percent of the muskrat populations and is prevalent in beavers (Erlandsen et al. 1988). Cryptosporidium parvum is found widely distributed in mammals, and zoonotic (animal to human) transmission has been well documented (Current 1987). Infections in cattle along with rainfalls, which washed the oocyst (the environmentally resistant and infectious form of the organism) into the water supply, were hypothesized as contributing to a large outbreak in the United Kingdom, resulting in 55,000 illnesses (Smith and Rose 1990). Cattle and sheep may represent a large reservoir for human infections. Both Cryptosporidium and Giardia can be found at prevalences of 68 percent and 29 percent, respectively, in polluted waters (waters receiving sewage and agricultural discharges) and 39 percent and 7 percent, respectively, in pristine waters (Rose et al. 1991b). In one watershed, animals were the major source of the contamination rather than sewage discharges (Rose et al. 1988). These studies suggest that domestic sewage discharges are a larger source of Giardia, while animals may be the major source of Cryptosporidium (Rose et al. 1991b). Among the bacteria, Salmonella, Yersinia, and Campylobacter are associated with animal reservoirs. Salmonellae are common in poultry (chickens, turkeys, ducks) and in gulls, pigeons, and doves but have been identified in other wild birds much less frequently (Feachem et al. 1983). Between 15 and 50 percent of domestic animals and 10 percent of mice and rats may be infected. Wild mammals do not appear to be a major source for human infections. Both wild and domestic animals may serve as reservoirs for Yersinia enterocolitica. The organism has been identified in foxes and beavers as well as cattle, sheep, and pigs. Campylobacter has been found in a wide variety of animals. Domestic animals (cattle, sheep, and pigs) and birds (poultry and caged birds) have been documented as sources of infections in humans. Animals may also contribute significant numbers of indicator bacteria (total coliforms, fecal streptococci, and enterococci) to waters (Crane et al. 1983). Gannon and Busse (1989) suggested that animals were the source of the elevated indicator bacterial levels in storm water. An epidemiological study of recreational waters has suggested that the indicator bacteria arising from agricultural inputs are not associated with human bacterial and viral infections (Calderon et al. 1991). Toxins in Shellfish and Fish Several illnesses are associated with the consumption of shellfish and fish as a result of toxic algal blooms (NRC 1991), including neurotoxic shellfish poisoning, paralytic shellfish poisoning, and scromboid poisoning (Table B.4).

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Managing Wastewater in Coastal Urban Areas TABLE B.4 Illnesses Associated with Consumption of Seafood and Associated with Toxic Algal Blooms (Adapted from NRC 1991) Toxins Source Epidemiology Symptoms Neurotoxic Shellfish Poisoning Red tide ''gymnodinium" accumulation in shellfish 53 cases reported 1973-88 Numbness, gastrointestinal effects, dizziness, muscle aches Paralytic Shellfish Poisoning Dinoflagellates accumulate in shellfish 137 cases reported 1978-85 Neurologic symptoms. paralysis, death Ciguatera Poisoning Reef algae gambiordiscus toxins in tropical reef fish 791 cases reported 1978-87 Gastrointestinal symptoms, neurological symptoms Scromboid Poisoning Histive production by bacterial contaminants during storage 757 cases reported 1978-87 Vomiting, diarrhea, headaches, palpitation The blooms of red tide, dinoflagellates, and reef algae are seasonal and in some cases geographically restricted. There has been some suggestion that nutrient additions to marine waters may affect size of blooms, frequency, and seasonality of occurrence (see Appendix A). Scromboid is believed to be due to improper handling of shellfish after harvest and no association with polluted marine waters has been suggested. OCCURRENCE OF PATHOGENS IN COASTAL WATERS In the United States, rarely are monitoring programs designed to determine level of pathogenic agents in marine waters. The bacteriological indicator system has been used primarily to determine the microbial quality of estuaries and recreational waters. No information is available on the occurrence of enteric protozoa in marine waters. Specialized studies have been directed at specific pathogenic bacteria, but the greatest amount of information on the occurrence of pathogens in marine waters has been reported for the enteric viruses. There may be several reasons for this. Viruses have

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Managing Wastewater in Coastal Urban Areas long been recognized as a major cause of shellfish associated disease. It has also been determined that the indicator concept is inadequate for determining viral water quality. Methods were developed for the recovery and detection of viruses and studies implemented as a result of the European Economic Community recognizing a need for virological monitoring. Past and ongoing studies continue to evaluate virus contamination of the marine environment in the United States. Bacteria With a better appreciation of the limitations of the indicator system, new methods are being used to detect the presence of bacterial pathogens in coastal waters. In a study in Spain, Salmonella was detected in 32 percent of 256 samples collected from 21 bathing beaches along the north coast (Perales and Audicana 1989). Similarly, 16 sites in New York Harbor, the Hudson and East rivers offshore in the Hudson River plume, Chester River, and the upper Chesapeake Bay were sampled for the presence of Salmonella (Knight et al. 1990). Salmonellae were detected at 75 percent of the sites and in 50 percent of these samples, cultivation techniques failed to isolate the organism. Previous work has demonstrated that non-cultivatable organisms can remain infectious (Colwell et al. 1985, Grimes and Colwell 1986). DePaola et al. (1990) investigated the occurrence of Vibrio parahaemolyticus in shellfish growing waters in Washington, California, Texas, Louisiana, Alabama, Florida, South Carolina, Virginia, and Rhode Island. They found no correlation of V. parahaemolyticus with fecal coliforms. Average densities were 3, 11, and 2.1 x 103/100 g of oyster in samples from the Atlantic, Gulf, and Pacific coasts, respectively. Concentrations were 100 times greater in oysters than in the water. Temperature appeared to be a significant factor in the seasonal and geographical distribution of this organism. Newly recognized bacterial pathogens have also been studied in coastal estuarine waters. Listeria monocytogenes has been associated with foodborne gastroenteritis. This organism was detected in 62 percent of the samples in the Humboldt-Arcata Bay in California. The organism was found in 17 percent of the sediment samples and was not detected in oysters. It was suggested that domestic animals, such as horses and cattle, were responsible for the contamination (Colburn et al. 1990). Enteric Viruses During the 1960s, several studies were published reporting the occurrence of enteroviruses in marine waters and shellfish (Metcalf and Stiles 1968, Bendinelli and Ruschi 1969). The next two decades brought with them improvements in the methods for the recovery and detection of enteric

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Managing Wastewater in Coastal Urban Areas viruses, which were applied to surveys primarily in the Gulf and Atlantic coastal areas. These advances made it possible to study the significance of viral contamination of marine waters, and currently the scientific consensus supports several conclusions. Enteric viruses persist significantly longer when compared with the bacterial indicators; There is no qualitative or statistical association between the enteric viruses and the bacterial indicators, and Enteric viruses have been isolated from both waters and shellfish within current bacterial standards for water quality. Table B.5 gives a summary of some of the more recent studies on the occurrence of viruses in shellfish and their overlying waters in areas opened and closed for harvesting based on the bacteriological indicators. In areas open to harvesting, viruses were recovered from 4 percent to up to 50 percent of the samples and levels ranged from 0.2 to 31 plaque forming units (PFU) per 100 grams of shellfish and 2.9 to 46 PFU/100 liters of water. Two locations were selected for study in Mississippi (Ellender et al. 1980). The waters of the Pass Christian reef were approved for shellfish harvesting. The Graveline Bayou was closed to harvesting due to influences by rainfall, tidal flushing, wastewater treatment plant discharges, and septic tanks. The year-long study demonstrated no significant correlations of the viruses with bacterial indicators, temperatures (4-32°C), or salinities (which would reflect fresh water inputs due to rain). Within the Texas Gulf coast, sewage outfalls may have been responsible for the contamination of the estuaries (Goyal et al. 1979). While rainfall was associated with increases in bacterial counts, it was not associated with viral contamination. Along the Atlantic coast, Wait et al. (1983) investigated viral and bacterial pathogens as well as the coliform indicators. Viruses were isolated without any correlation with the indicator system. Researchers investigating the Oyster River system in New Hampshire (A.B. Margolian, University of New Hampshire, personal communication, 1992) recently speculated that wastewater treatment plant discharges and septic tank leachate to rivers, which then flow into estuaries, are responsible for the viral contamination of the water as opposed to a sewage outfall. Although fewer studies have been directed toward recreational areas, there is evidence that sewage outfalls can impact bathing beaches. Along the shoreline of South Wales, viruses were isolated from 35 to 50 percent of the bathing beaches at levels averaging 21 PFU/100 liters. Wastewater treatment plant discharges from a short outfall were the most probable source of the contamination, as no other source of human enteric viruses could be

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Managing Wastewater in Coastal Urban Areas TABLE B.5 Enteric Virus Isolations from Shellfish Harvesting Areas     Open Shellfish Beds1 Closed Shellfish Beds1 Area State or Location Water (%)2 PFU3 Shellfish Water Shellfish Gulf Michigan (Ellander et al. 1980) ND4 (9%) 1.95 ND4 (34%) 1.02   Texas (Goyal et al. 1979) (50%) 2.9 - 185 (20%) 19 (63%) 4.8 - 11 (40%) 47 - 94 Atlantic North Carolina (Wait et al. 1983)           Central ND (25%) 0.2 ND (37%) 1.85   Southern ND (12%) 6.0 ND (37%) 0.35   New Port River Estuary System (Carrick et al. 1991)     1.276 0.436   New Jersey (4.3%) 46 (40%) 8.0 (43%) 36 (28%) 4.3   New York (Vaughn et al. 1980) (12%) 9.2 (25%) 31.0 (0%) (37%) 9.5 1 Based on bacteriological indicators standards. 2 Percent of samples positive for viruses. 3 PFU/100 liters water/100 grams shellfish. 4 Not determined. 5 Ranges. 6 Two of 11 stations positive for viruses were within total and fecal coliform standards for microbial contamination.

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Managing Wastewater in Coastal Urban Areas TABLE B.8 Probability Models Used for Microorganisms (Haas 1983) single-hit exponential model p = 1 - exp(-rN) beta-distributed ''infectivity probability" model p = I - [I + (N/ß)]-a p = probability of infection (risk) N = exposure a, ß, r = parameters characterized by dose response curves interactions are constant, then the probability of an infection resulting from ingestion of a single exposure containing an average number of organisms may be given by an exponential model. An alternative model that has a better fit with experimental data is the beta-distributed model (Table B.8) (Furumoto and Mickey 1967a and 1967b; Haas 1983). Using these models, dose response curves were plotted for a number of pathogens for a number of studies using the maximum likelihood method (Regli et al. 1992). The Rotavirus and Poliovirus 3 were found to be more infective than the Echovirus 12 and Poliovirus 1 (Figure B.3). This may have been due to the use of nonvirulent strains. The probability of infection from exposure to one viral unit ranged from 2.8 x 10-1 to 7.2 x 10-5. The development of clinical illness (symptoms) depends on numerous FIGURE B.3 Dose response relationships for various enteric viruses (Regli et al. 1992).

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Managing Wastewater in Coastal Urban Areas factors, including the immune status of the host, age of the host, virulence of the microorganisms and type, strain of microorganism, and route of infection. Clinical illness may also be influenced by the dose (Haas 1983, Graham et al. 1978). For hepatitis A virus, the percentage of individuals with clinically observed illness is low for children (usually < 5 percent) but increases greatly with age (Evans 1982). The frequency of clinical hepatitis A virus in adults is estimated at 75 percent. However, during waterborne outbreaks, it has been observed as high as 97 percent (Lednar et al. 1985). In contrast, the frequency of clinical symptoms for rotavirus is greatest in childhood (Gerba et al. 1985) and lowest in adulthood. The observed illness rates for various enteroviruses may range from 1 percent for poliovirus to more than 75 percent for some of the coxsackie B viruses (Cherry 1981) (Table B.9). Case fatality rates are also affected by many of the same factors that determine the likelihood of the development of clinical illness. The risk of mortality for hepatitis A virus has been estimated at 0.6 percent (CDC 1985). Mortality from other enterovirus infections in North America and Europe has been reported to range from < 0.1 to 1.8 percent (Assaad and Borecka 1977). Case fatality rates for selected enteroviruses are summarized in Table B.9. The values for enteroviruses probably only represent hospitalized cases. For some pathogens, the risk of infection may be low but the consequences of infection may be more drastic. Therefore, infectivity and case fatality rates can be added to the model to further estimate disease and death. The ultimate aim of developing standards, treatment approaches, and intervention strategies is to provide an acceptable degree of protection for the susceptible population. A risk assessment model targeting infection can be used to emphasize the initial step in the chain of events that leads to the mortality associated with waterborne or foodborne pathogens. Since infec- TABLE B.9 Morbidity and Mortality Rates Associated with Various Viral Pathogens (Assaad and Borecka 1977, Cherry 1981, Evans 1982, CDC 1985, Gerba et al. 1985, Lednar et al. 1985.) Microorganism Morbidity Rates (%) Mortality Rates (%) Poliovirus 1 1 0.01 Rotavirus 56 0.01 Hepatitis A virus (in children) 5 not known Hepatitis A virus (in adults) 75 0.6

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Managing Wastewater in Coastal Urban Areas tion is the primary event that leads to disease, by preventing infection one prevents any range of morbidities and mortalities associated with the pathogen. Secondary spread of enteric infections range from 30 to 70 percent. Thus three to seven of ten individuals who came into contact with the first infected person may also become infected. Prevention of initial infections will also prevent the rippling effect of secondary spread. Exposure Assessment One can use these models once exposure has been determined. For example, viral contamination of recreational waters at levels between 0.1 to 100 PFU/100 liters may be associated with risks of infection from 2 x 10-7 to 5.4 x 10-2 depending on the type of virus and assuming ingestion of 100 ml during each swimming event. Limited studies have been undertaken to evaluate virus contamination in shellfish. Viruses were found in 9 to 40 percent of the shellfish in waters open to harvesting and in 13 to 40 percent of the shellfish in areas closed due to coliform levels in the water. The concentrations of enteroviruses ranged from 10 to 200 virus plaque-forming units per 100 grams of shellfish. Table B.10 shows the results of four studies on virus contamination of shellfish in waters open to harvesting, based on the bacterial indicator. Studies have determined that for an average meal, 6 to 12 shellfish ranging in weight between 10 and 20 grams each may be consumed (M.D. Sobsey, University of North Carolina, personal communication, 1992). These values were used to determine virus levels in a risk assessment model to evaluate potential health impacts of consuming raw shellfish. Application of a Virus Risk Model to Characterize Risks from Consuming Shellfish It is well known that infectious hepatitis and viral gastroenteritis are caused by consumption of raw or, in some cases, cooked clams and oysters. The number of documented viral outbreaks seems to be on the increase in the United States (DeLeon and Gerba 1990). Using the data presented in Table B.10 and the Echo-12 virus probability model, the individual risk was determined for consumption of raw shellfish (Table B.10). The percentage of samples contaminated with viruses ranged from 9 percent (Mississippi oysters) to 40 percent (New York clams). The levels of viruses ranged from 0.3 to 200 viruses/100 grams. In the model, one exposure was used, representing a single serving of six shellfish (60 grams). Risks ranged from 3.5 x 10-2 to 2.2 x 10-4, and on average there is a 1/100 chance of infection when consuming raw shellfish. The risk calculations are shown below:

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Managing Wastewater in Coastal Urban Areas TABLE B.10 Risk of Infection for a Single Serving of Shellfish from Samples of Viral-Contaminated Shellfish Based on Infectivity of Echovirus (Goyal et al. 1979, Ellender et al. 1980, Vaughn et al. 1980, Wait et al. 1983.) Study Site Shellfish Total Samples Collected Total Samples Positive (levels)1 Average Viruses (PFU/100g) Individual2 Risk Mississippi Oysters 22 2(0.3) 0.18 2.2 x 10-4       (3.6)     New York Clams 5 2(10) 8.0 9.4 x 10-3       (30)     New York Oysters 8 2(48) 31.0 3.5 x 10-2       (200)     North Carolina Clams 13 3(0.8) 3.8 4.5 x 10-3       (48)     Texas Oysters 10 2(17) 7.6 9.0 x 10-3       (59)     Total/Averages   58 11 10.0 1.2 x 10-2 1 Levels are PFU/100 grams. 2 Consuming 60 grams.

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Managing Wastewater in Coastal Urban Areas where, P = the probability of infection, N = exposure as measured in PFU/60 grams. Morbidity and mortality risks can be estimated from probabilities of infection and will vary depending on the virus. Figure B.4 compares infection, illness, and death risks for rotavirus and hepatitis A virus (HAV). (The Echo-12 virus model was used in the absence of a model for HAV.) The morbidity rates used were 56 percent for rotavirus and 75 percent for HAV as shown in Table B.9. The mortality rates used were those shown on Table B.1. Exposure was set for a small serving (60 g) of shellfish with contamination ranging from 0.1 to 100 viruses per serving. These exposures correspond to virus concentration levels ranging from 0.17 to 177 viruses per 100 grams and are within the ranges detected in surveys of shellfish from waters open to harvesting in the United States (see Table B.10). The risk of infection is more than 10 times greater for rotavirus than HAV if one assumes HAV infectivity is similar to Echo-12; however, mortality is much more significant for HAV infections. For even a single serving of shellfish that is greatly contaminated with viruses, the risk of death is very high at between 1.7 x 10-3 to 7.8 x 10-3. The risk of becoming infected with the exposure to even one virus was estimated at between 10-1 to 10-2. SUMMARY OF SHELLFISH AND RECREATIONAL MICROBIOLOGIC RISKS Acceptable recreational risks based on indicator bacterial levels and epidemiological studies have suggested an acceptable risk level of 8 x 10-3 (Cabelli et al. 1983). This risk would correspond to between 1 rotavirus and 100 echoviruses per 100 milliliters. However, these same concentrations in the water column can lead to concentrations 100 to 900 times as large in underlying sediments underlying and shellfish. This concentration would increase virus levels to between 0.1 and 100 viruses per 60 grams (representing a single meal of 6 oysters for example) accordingly (Figure B.4). Therefore, protective levels for bathing water may be inadequate to protect against food-borne infections.

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Managing Wastewater in Coastal Urban Areas FIGURE B.4 Risks of infection, disease, and mortality for contaminated shellfish (Rose and Sobsey undated). Risk assessment may be used to evaluate potential health impacts of food or water contaminated with pathogens. However, it is important to be cautious in interpreting monitoring data; most methods do not recover more than 40 percent of the organisms present; and therefore the exposure may be underestimated. Past surveys may not be useful for prediction of future contamination due to the variation in concentrations of microbial pathogens and the differences in die-off rates in the environment. Several factors will influence the significance of wastewater inputs associated with risks from microbial pathogens. The level of infection in the human and animal populations producing the wastes will influence the initial concentrations. It is likely that large cosmopolitan cities with larger immigrant populations have a greater concentration and variety of pathogens present in their sewage. Cities such as Los Angeles, San Francisco, Miami, and New York may fall into this category. Coastal water temperatures will influence the survival of the pathogens and the potential for regrowth of the coliforms. The warmer waters in the Gulf and off the southern Atlantic states may enhance the inactivation rates for pathogens while enhancing the potential for inputs of coliforms that have grown in fresh water environments. There is no doubt that the cooler temperatures of the waters off the west coast and northeast coast will maintain pathogen viability for a longer period of time. Of greatest concern are combined sewer overflows which carry untreated wastes, and short outfalls, which have the potential for contributing

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Managing Wastewater in Coastal Urban Areas to microbial contaminants that can be transported back to shore. Wastewater treatment plants that achieve secondary treatment remain a threat to recreational areas and shellfish harvesting areas by direct discharge through short outfalls or through discharge to freshwaters, which then flow into the marine environment. Enteric viruses remain the primary concern for any wastewaters carrying human sewage (Asano et al. 1992). Secondary treatment and disinfection, operated and monitored for the 200 fecal coliform per 100 ml standard, do not guarantee the removal of such pathogens to levels that are safe for discharges close to shellfish beds or bathing areas. See Appendix D for discussion of wastewater treatment options, disinfection procedures, and combined sewer overflow controls. Despite requirements that shellfish harvesting waters must meet established bacterial indicator standards and sanitary survey criteria, disease outbreaks due to consumption of contaminated shellfish continue to occur in the United States. For example, a recent outbreak of hepatitis A virus associated with shellfish consumption affected several southern states. The virus was detected in shellfish harvested from waters approved for harvesting (Desenclos et al. 1991). There is no doubt that such outbreaks should be prevented. Better detection methods and risk assessment methods are needed in order to provide adequate protection of consumers from disease transmitted through the nation's seafood. Disease transmission through exposure to recreational waters has been demonstrated, however, the associated risks are not as well documented as those for seafood consumption. The development of better detection techniques, additional epidemiological information, and improved risk assessment methodologies will allow for more certain determinations of the risks associated with recreational exposure to contaminated waters and the development of better recreational water protection strategies. REFERENCES Alexander, L.M., A. Heaven, A. Tennant, and R. Morris. 1992. Symptomatology of children in contact with sea water contaminated with sewage. J. Epid. Commun. Hlth. 46:340-344. Asano, T., L.Y.C. Leong, M.G. Rigby, and R.H. Sakaji. 1992. Evaluation of the California wastewater reclamation criteria using enteric virus monitoring data. Water Science and Technology 26(7-8):1513-1524. Assaad, F., and I. Borecka. 1977. Nine-year study on WHO virus reports on fatal virus infections. Bulletin of the World Health Organization 55:445-453. Balarajan, R., V.S. Raleigh, P. Yuen, D. Wheeler, D. Machin, and R. Cartwright. 1991. Health risks associated with bathing in sea water Brit. Med. J. 303:1444-1445. Bendinelli, M. and A. Ruschi. 1969. Isolation of human enterovirus from mussels. Appl. Microbiol. 18:531-532. Bennett, J.V., S.D. Homberg, M.F. Rogers and S.L. Solomon. 1987. Infectious and parasitic diseases. Am. J. Preventative Med. 55:102-114.

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