Microbial hazards considered for this study

Escherichia coli (E. coli)

Escherichia coli is a normal inhabitant of the gastrointestinal tract of humans and other

warm-blooded animals and is often considered a harmless organism. It is a member of the total coliform group but is considered as the most specific indicator of faecal pollution and is therefore used as a standard to indicate the presence of faecal contamination of environmental and food samples [22, 75]. The presence of E. coli is also likely to indicate the presence of other disease causing organisms such as pathogenic bacteria, viruses and protozoans though it is a poor indicator for viruses and protozoans that can survive much longer than the bacteria indicator [75]. However, several strains are pathogenic and can cause gastroenteritis; among these are enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), enteroaggregative

E. coli (EAEC), enteroinvasive E. coli (EIEC), and enterohemorrhagic E. coli (EHEC) [22].

These strains are grouped by their mechanisms of pathogenesis and are spread by the faecal- oral route of transmission. Pathogenic E. coli are known to cause several diarrhoea related diseases including traveller’s diarrhoea especially in persons from industrialised countries, chronic childhood diarrhoea and infant diarrhoea. While some of these diarrhoea related diseases can be mild and last up to a period of 5 days, others can also be very severe and prolonged or persistent lasting more than 14 days and with a case fatality rate as high as 50% [22]. EAEC in particular is associated with persistent diarrhoea and is a major cause of illness and death in children. Some victims can also develop haemolytic-uremic syndrome (HUS), which can result in renal failure and haemolytic anaemia or can result in permanent loss of kidney. Most outbreaks of pathogenic E. coli have been associated with food such as raw beef and chicken, undercooked or raw hamburger, unpasteurized milk and fruit juices, and vegetables contaminated with cow dung. Waterborne outbreaks occur through nondisinfected groundwater and recreational waters. For example studies have shown that E. coli O157:H7 is commonly found in domestic sewage at levels from 10 to 100 CFU/100 ml and in wastewater from slaughter-houses from 100 to 1000 CFU/100 ml [22].

33 Norovirus

Noroviruses belong to the family of Calicividae and is one of two genera (the other being

Sapoviruses) that is known to infect humans [22]. They are also nonenveloped viruses with a

diameter of approximately 26 to 35 nm and a positive-sense ssRNA genome [76]. Although there are several genotypes of noroviruses, the genotypes GI (NV-GI) and GII (NV-GII) are the most common types identified to cause illness [22]. Noroviruses are major causes of both food and water borne disease and can infect both children and adults. NoVs are the leading cause of food-borne outbreaks of acute gastroenteritis and the most common cause of sporadic infectious gastroenteritis affecting people of all age group [77, 78]. NoV food-borne outbreaks often result from the consumption of shellfish, fresh produce and ready to-eat food contaminated by infected, but possibly asymptomatic, food handlers [79, 80]. Age is a significant factor associated with norovirus infections and related deaths. For example, a review of norovirus infections resulting in 158 associated deaths in 12 countries showed that for age related data, 61% of the deaths were found in those above 65 years of age with 22% and 17% occurring in age groups less than 2 years of age and between 49 and 65, respectively. Norovirus usually produce a mild and brief illness, lasting between one and two days. The disease is characterized by nausea and abdominal cramps, followed commonly by vomiting in children and diarrhoea in adults [22]. Mortality does occur but usually only in immunocompromised individuals or the elderly [81]. The virus is often transmitted by ingestion of food or water contaminated with faecal matter, or by direct or indirect contact and also via aerosol [22]. Norovirus can also be spread by contaminated surfaces or formites (inanimate objects) such as toilet flush handles and doorknobs and are especially common in environments such as schools, hotels, summer camps and hospital emergency rooms [22, 82]). Through epidemiological studies, public toilets have also been shown to be responsible for outbreaks of pathogens including norovirus [22]. The transmission of noroviruses is enhanced by its low infectious dose – fewer than 10 particles could cause infection [57], high resistance to disinfection [83] and long term stability and survival in the environment [82, 84]. NoV is also resistant to many industrial food preservation methods and can survive chilling, freezing, acidification, reduced water activity and modified atmosphere packaging [85]. Additionally, there are reported outbreaks of NoVs in sewage polluted drinking water due to NoVs high resistance to wastewater treatment and high persistence in aquatic environment [86, 87].

34 Adenovirus

Adenoviruses are double-stranded DNA (dsDNA) icosahedral viruses approximately 70 nm in diameter and belong to the Adenoviridae family of viruses [76]. Adenoviruses cause a wide variety of illnesses in humans from eye infections to diarrhoea. There are about 57 known types of adenoviruses that infect man, with most of these human illnesses associated only with one-third of adenovirus types [22]. Adenovirus types 31, 40, 41, and 52 are known to cause gastroenteritis. The enteric adenoviruses 40 and 41 have also been recognized as the second most important etiological agents of viral gastroenteritis in children [88, 89]. These viruses are also transmitted through the oral-faecal route. Adenoviruses have also been found to have enhanced survival in water, large concentrations in untreated sewage or sewage polluted waters and high resistance to UV light disinfection [22, 90, 91]. Although norovirus was the key virus considered in the health risk assessment for this PhD research, some information on the presence and concentrations of adenovirus in various environmental and food samples (e.g. irrigation water, soil and raw lettuce) that were collected in this study have been included at appropriate sections in this thesis. The objective was to provide researchers and other stakeholders with this information especially for those who are interested and likely to do further research on adenovirus in this research area.