Escherichia coli O157 Infection in Man

Escherichia coli O157

E. coli is a bacterium, many strains of which live harmlessly in the gastro-intestine of both animals and humans (Anon., 1997d). E. coli O157 is a recently emerged pathogen in an evolutionary scale, with its first report as a cause of human illness in the United States in 1982 (Riley et al., 1983; Anon., 2001c). The main evolutionary tool of E. coli O157 is its enhanced ability to acquire useful foreign DNA (Whittam et al., 1998). It has been hypothesised that E. coli O157 evolved from an enteropathogenic E. coli ancestor that acquired virulent factors (e.g. genes encoding for shiga toxin production) from other organisms, both E. coli and non-E. coli species culminating in the zoonotic pathogen that exists (Law, 2000).

E. coli O157 Human Infection

E. coli O157 is a member of a group of zoonotic pathogens, verotoxigenic E. coli (VTEC) which were first detected in the US in 1982 (Riley et al., 1983). Non- O157 VTECs, for example E. coli O26, E. coli O111 and E. coli O113 have also been isolated from clinical cases worldwide (Anon., 1998d; Beutin et al., 1998; Keskimaki et al., 1998; Reilly, 1998; Anon., 2000a; Brooks et al., 2004). VTEC O157 has been detected worldwide including the United States and associated with several large and high profile outbreaks (Marsh et al., 1992; Kohli et al., 1994; Watanabe et al., 1999; Cowden et al., 2001).

In New York the annual incidence rate for E. coli O157 per 100,000 population has ranged from 1.6 in 1995 to 8.5 in 1999 (Chang et al., 2004). In 2006 a total of VTEC O157 (590), VTEC non-O157 (209) were recorded in 10 States by Foodnet in the US (Anon, 2007). VTEC O157 is the most commonly reported VTEC in Ireland, accounting for 96% of the recorded VTEC infections in man in Ireland since 2001 (Foley and McKeown, 2002a; Garvey et al., 2003).

The clinical manifestations of VTEC O157 infection in man includes freedom from symptoms; non-bloody diarrhoea; haemorrhagic colitis; haemolytic uraemic syndrome (HUS); thrombotic thrombocytopaenic purpura (TTP) (Swerdlow and Griffin, 1997; Todd and Dundas, 2001). The non-bloody diarrhoea can remain mild or become severe. However, in some cases the non-bloody diarrhoea may become haemorrhagic on the second or third day from the onset of diarrhoea (Mead and Griffin, 1998). The symptoms of haemorrhagic colitis include severe abdominal haemorrhage followed by bloody diarrhoea, oedema, erosion or haemorrhage of the mucosal lining of the colon. It has been estimated that 1% of haemorrhagic colitis cases die without progressing to HUS (Anon., 1999c).

In sporadic cases three to seven percent of cases progress to HUS. However, in outbreaks the percentage of cases progressing to HUS may increase to 20% or more (Mead and Griffin, 1998). In New York the annual incidence rate for diarrhea-associated HUS per 100,000 population has ranged from 0.1 in 1995 to 0.2 in 1999 (Anon, 2007). HUS is typically diagnosed six days after the onset of diarrhoea. Of the patients that develop HUS approximately three to five percent die, five percent develop chronic renal failure, strokes and other major sequelae, 30% develop proteinuria and other major sequelae and 60% resolve (Mead and Griffin, 1998).

TTP is a further potential complication of haemorrhagic colitis, which mainly affects adults rather than children. TTP is a serious illness involving haemorrhage due to a clotting deficiency. The clinical syndrome is predominantly neurological (Anon., 1999c). A significant facet of this disease is that vulnerable sectors of society, namely children and the elderly, are most at risk of developing severe VTEC O157 disease (Mead and Griffin, 1998; Duffy et al., 2000; Todd and Dundas, 2001).

Sources of E. coli O157 human infection

The first reported outbreak of VTEC O157 infection in man was linked to eating undercooked beef burgers in Oregon in 1982 (Riley et al., 1983). Since then, a proportion of VTEC O157 outbreaks have involved either hamburgers or ground (minced) beef products (Todd, 2000). For example 48 of 80 VTEC O157 outbreaks in the USA during 1998 and 1999 reported by the Centers for Disease Control and Prevention (CDC) were associated with food, and beef and beef products accounted for 21 of these food associated VTEC O157 outbreaks (Anon., 1999d; Anon., 2000b). In 2007 there were several large multi-State outbreaks of E. coli O157. Fresh spinach and beef were the sources of the E. coli O157 infection in the large outbreaks. In the September outbreak VTEC O157 was isolated from Topp's brand frozen ground beef patties. This lead the USDA to recall 21.7 million pounds of beef. Over the course of the outbreak 33 people were hospitalized and two patients developed HUS (Anon., 2007a). Studies of sporadic cases of VTEC O157 illness in the USA have identified ground beef as the substantial source of human exposure to the pathogen (MacDonald et al., 1988; Le Saux et al., 1993; Mead et al., 1997; Slutsker et al., 1998).

Many other foodborne sources of VTEC O157 infection have also been identified over the past 20 years. Foods such as cheese, milk and sprouts have also been associated with outbreaks worldwide (Chapman et al., 1993; Anon., 1998c; Durch et al., 1999; Breuer et al., 2001). In 2000 a large Canadian outbreak, in which 2,300 people became ill and seven people died was associated with E. coli O157 contamination of the water supply (Hrudey et al., 2003). Contamination of a water supply was associated with a local herd of cattle shedding E. coli O157 in their faeces. An increasingly reported and important source of infection for man is direct and indirect contact with ruminants (cattle, sheep, goats and deer) (Smith et al., 2001b; Warshawsky et al., 2002; Woodward et al., 2002; Payne et al., 2003).

Other species have also been implicated as a source of VTEC O157 infection. A report published in 2002 described a case in which rabbits were implicated in contaminating a children’s playground (Bailey et al., 2002). Following investigation, it was found that rabbits and humans along with cattle from a neighboring herd all shed an indistinguishable VTEC O157 strain. In conclusion, there are a large variety of potential sources of VTEC O157 infection for man. Ruminants and in particular cattle are an important potential source of infection to man via direct and indirect contact and animal products such as ground beef.

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