Subsequent investigations confirmed the link between STEC infection and cases of diarrhoea, haemorrhagic colitis, haemolytic uraemic syndrome and thrombotic thrombocytopenic purpura (12), and also revealed there are two main types of Shiga toxin, Stx1 and Stx2.
As a result, Stx2 is the variant most often associated with clinical cases of STEC and the progression of such cases to haemorrhagic colitis and haemolytic uraemic syndrome (21,27).
Most of the strains isolated from outbreaks of haemorrhagic colitis and haemolytic uraemic syndrome, and those infections with more severe symptoms, typically express both Stx and intimin along with carriage of pO157 (30, 31, 36), and are usually designated as the pathotype enterohaemorrhagic E.
The progression to haemorrhagic colitis and haemolytic uraemic syndrome is difficult to predict (19), but is especially frequent in children <10 years of age (35, 42), the immunocompromised and the elderly, with the highest rates associated with EHEC ([stx.sup.+], [eaeA.sup.+]) and particularly O157 serotypes (21, 35).
coli 0157:H7, the primary serovar associated with haemorrhagic colitis and haemolytic uraemic syndrome.
Alongside these media is Rhamnose MacConkey (VTEC 026) Agar, selective for verocytotoxin producing E.coli 026, a strain that is also associated with haemorrhagic colitis and haemolytic uraemic syndrome.