Escherichia coli O157 was first identified as a human pathogen in 1982
. One of several Shiga toxin-producing serotypes known to cause human
illness, the organism probably evolved through horizontal acquisition
of genes for Shiga toxins and other virulence factors. E coli O157 is
found regularly in the faeces of healthy cattle, and is transmitted to
humans through contaminated food, water, and direct contact with infe
cted people or animals. Human infection is associated with a wide rang
e of clinical illness, including asymptomatic shedding, non-bloody dia
rrhoea, haemorrhagic colitis, haemolytic uraemic syndrome, and death.
Since laboratory practices vary, physicians need to know whether labor
atories in their area routinely test for E coli O157 in stool specimen
s. Treatment with antimicrobial agents remains controversial: some stu
dies suggest that treatment may precipitate haemolytic uraemic syndrom
e, and other studies suggest no effect or even a protective effect. Ph
ysicians can help to prevent E coli O157 infections by counselling pat
ients about the hazards of consuming undercooked ground meat or unpast
eurised milk products and juices, and about the importance of handwash
ing to prevent the spread of diarrhoeal illness, and by informing publ
ic health authorities when they see unusual numbers of cases of bloody
diarrhoea or haemolytic uraemic syndrome.