Guidelines for Canadian Drinking Water Quality: Supporting Documentation - Enteric Viruses

Health Effects

Effects in Humans

While the symptoms most commonly associated with enteric viral infections are gastroenteritis and/or diarrhoea, some enteric viruses are also responsible for respiratory symptoms, central nervous system infections (aseptic meningitis, poliomyelitis), hepatic infections and muscular syndromes (fibromyalgia, myocarditis) and have been implicated in some forms of diabetes and chronic fatigue syndrome (Payment 1993; Fields et al. 1996; Murray 1999; Chin 2000).

Noroviruses

Norovirus outbreaks affect infants, children and adults. Health effects associated with norovirus infections tend to be mild and are self-limiting, typically lasting 24-48 hours. Symptoms include nausea, vomiting, diarrhoea, abdominal pain and fever. The infectious dose is unknown but presumed to be low. The incubation period is 24-48 hours (Kapikian et al. 1996; Chin 2000). Many of the cases of norovirus gastroenteritis have been associated with groups of people living in a close environment, such as schools, recreational camps, institutions and cruise ships.

Hepatitis Viruses

There are five types of hepatitis virus; however, only two types (HAV and HEV) appear to be transmitted via the faecal-oral route and have been associated with waterborne transmission. HAV infections, commonly known as infectious hepatitis, can cause liver damage leading to death. The infectious dose is unknown but is estimated to be 10-100 virus particles. The incubation period of HAV infection is between 10 and 50 days, with an average of approximately 28-30 days. The incubation period is inversely related to dose: the greater the dose, the shorter the incubation period. Symptoms include fever, malaise (fatigue), anorexia, nausea and abdominal discomfort, followed within a few days by jaundice. The illness is usually self-limiting, but mortality can reach 2% in adults over 40 years of age. The virus is excreted in the faeces of infected persons for 1-2 weeks before the development of hepatitis and is spread via the faecal-oral route (Hollinger and Tricehurst 1996; Chin 2000).

The disease caused by HEV is called hepatitis E, or enterically transmitted non-A non-B hepatitis. Hepatitis E infection is clinically indistinguishable from hepatitis A infection. Symptoms include malaise, anorexia, abdominal pain, arthralgia and fever. The infectious dose is not known. The incubation period for hepatitis E varies from 2 to 9 weeks. Hepatitis E infection is usually mild and resolves in 2 weeks, leaving no sequelae. The fatality rate is 0.1-1%, except in pregnant women, for whom the fatality rate can approach 20%. The illness is most often reported in young to middle-aged adults (15-40 years old).

Rotaviruses

Rotavirus gastroenteritis can result in mild diarrhoea lasting for less than 24 hours or in more severe gastroenteritis that can be fatal. Vomiting can occur for up to 48 hours prior to the onset of gastroenteritis. The incubation period is about 19 hours to 2 days. The illness generally lasts between 5 and 8 days. The infective dose is presumed to be 10-100 infectious viral particles (Graham et al. 1987).

Group A rotavirus is endemic worldwide and is the most common and widespread group. Infections are referred to as infantile diarrhoea, winter diarrhoea, acute non-bacterial infectious gastroenteritis and acute viral gastroenteritis. Children 6 months to 2 years of age, premature infants, the elderly and the immunocompromised are particularly prone to more severe symptoms caused by infection with group A rotavirus. It is the leading cause of severe diarrhoea among infants and children and accounts for about half of the cases requiring hospitalization. In the United States, approximately 3.5 million cases occur each year (Glass et al. 1996). In temperate areas, it occurs primarily in the winter; in the tropics, it occurs throughout the year (Moe and Shirley 1982; Nakajima et al. 2001). Outbreaks caused by Group B rotavirus, also called adult diarrhoea rotavirus, have also been reported in the elderly and adults, although infection in the latter is very uncommon and usually subclinical. Group C rotavirus has been associated with rare and sporadic cases of diarrhoea in children in many countries. However, the first outbreaks were reported from Japan and England (Caul et al. 1990; Hamano et al. 1999).

Enteroviruses

The main route of infection for enteroviruses is oral, and their incubation period ranges from 2 to 35 days, with a median of 7 to 14 days. Enteroviruses can survive transit through the stomach and infect the lower intestinal tract. Viraemia (i.e., passage in the bloodstream) is frequent, and passage to various target organs results in a range of symptoms. The most serious complications include poliomyelitis and meningitis. Other complications include myalgia, Guillain-Barré syndrome, hepatitis, febrile illnesses and conjunctivitis. Enteroviruses are endemic worldwide, but few water-related outbreaks have been reported. Enteroviruses remain a significant public health concern in developing countries. The large number of serotypes, the usually benign nature of the infections and the fact that they are highly transmissible in a community by personal contact probably explain why so little is known of their transmission by the water route (Field et al. 1968; Lenaway et al. 1989; Ikeda et al. 1993; Kee et al. 1994; Melnick 1996; Jaykus 2000; Lees 2000; Amvrosieva et al. 2001).

Other Enteric Viruses

Human adenoviruses can cause both respiratory and gastrointestinal illnesses. Adenoviral gastroenteritis occurs mainly among young children. The incubation period ranges from 1 to 3 days. Symptoms include diarrhoea and vomiting. Adenoviruses can be transmitted by direct contact, via the faecal-oral route or through recreational water; drinking water has not been reported as a route of transmission.

Astrovirus infection usually results in symptoms very similar to those observed for rotavirus infection and affects mainly young children. The incubation period ranges from 1 to 4 days. Astroviruses are transmitted via the faecal-oral route, through recreational water or food; drinking water has not been reported as a route of transmission.

Parvovirus infection usually results in a mild flu-like illness, sometimes accompanied by a rash ("fifth disease"). Complications, including anaemia and joint pain, can occur among pregnant women and the immunocompromised. The incubation period ranges from 4 to 14 days. The role of parvoviruses in human gastroenteritis is uncertain. There is limited evidence of parvovirus transmission through food (shellfish) and recreational water; drinking water has not been reported as a route of transmission.

Outbreaks

Waterborne enteric viruses are a common cause of outbreaks worldwide, and some of the viral agents responsible for these outbreaks have only recently been identified (Craun 1986, 1992; Fields et al. 1996; Payment and Hunter 2001). The true prevalence of viral waterborne outbreaks is unknown.

In the United States, between 1980 and 1994 (1984 data missing), 28 outbreaks and 11 195 confirmed cases of waterborne viral illness were reported. Of these, 9038 cases were attributed to noroviruses, and 396 cases were attributable to HAV. An outbreak among adults arising from rotavirus contamination of a municipal water supply was reported (Hopkins et al. 1984). HAV outbreaks have occurred in day care centres and institutions due to a breakdown in hygienic conditions or contamination of food or water (MMWR 1980-1994; Gerba et al. 1985; Hollinger and Tricehurst 1996; AWWA 1999b; Chin 2000). During these periods, many outbreaks of unknown etiology were also reported. It is likely that enteric viruses were responsible for a significant portion of these outbreaks (MMWR 1980-1994; Craun 1986, 1992).

In Canada, between 1974 and 1995, there were 21 reported outbreaks and 1358 confirmed cases of waterborne illness caused by enteric viruses. Eleven of these outbreaks were attributed to HAV, eight were attributed to noroviruses, one to rotavirus and one to a virus of unknown etiology (Health Canada 1974-1995). Of the 11 reported outbreaks attributed to waterborne HAV, four were due to contamination of public drinking water supplies and seven were due to contamination of private water supplies (Health Canada 1974-1995). All eight of the reported waterborne outbreaks of norovirus infections in Canada occurred in public water supplies (Health Canada 1974-1995). The rotavirus outbreak arose from contamination of a public drinking water supply.

Major waterborne epidemics of HEV have occurred worldwide, but none has been reported in North America, although there is no evidence of immunity against this agent in the North American population (Purcell 1996; Chin 2000). The astroviruses, adenoviruses and parvoviruses are enteric viruses that have been implicated in recreational water and foodborne (seafood) outbreaks. Drinking water-associated outbreaks have not been reported, but the development of new detection methods could change this (Martone et al. 1980; Turner et al. 1987; Hedberg and Osterholm 1993; Gray et al. 1997; Kukkula et al. 1997, 1999; Lees 2000).