Zoonotic infections infections in livestock and the risk to public health

VTEC: How important is it?

S J O'Brien

Since it was first discovered to be a pathogen in the late 1970s, Vero cytoxoin-producing Escherichia coli (VTEC) have made their presence felt worldwide. Large outbreaks in the United States of America, central Scotland, Japan and, most recently, in Canada highlight the morbidity and mortality associated with this organism.

In the United Kingdom the predominant pathogen is VTEC O157 and 1,429 cases were confirmed by the PHLS Laboratory of Enteric Pathogens (LEP) and the Scottish E. coli O157 Reference Laboratory in 1999. The majority of cases are sporadic.

The features of VTEC O157 infection which make it so important are:-

the substantial morbidity and mortality associated with infection

Severe complications of VTEC O157 infection include haemolytic uraemic syndrome (HUS), which mainly affects children, and thrombotic thrombocytopoenic purpura (TTP), particularly in adults. Both these complications carry significant mortality. For children developing HUS who survive a substantial proportion suffer long term renal damage.

the fact that infection is not treatable

Therapeutic options are very limited. The mainstay of therapy includes correcting and maintaining fluid and electrolyte balance and monitoring patients for the development of HUS. A recent cohort study from the United States lends further evidence that antibiotic treatment might do more harm than good.

the range of modes of transmission and low infectious dose

Although VTEC O157 infection was first recognised as foodborne, evidence accumulated from outbreak investigations and from studies of sporadic cases demonstrates several modes of transmission from the animal reservoir (food-, water-, environment- and animal-to-person). Person-to-person transmission has also been demonstrated in outbreaks in households, nurseries, hospitals and nursing homes. Spread of infection by any of these means is facilitated by the fact that the infectious dose is, apparently, so small.

the enormous cost in social and economic terms

The economic consequences of VTEC O157 are considerable, the cost of a single (large) outbreak having been estimated at £171,848, with the cost over 30 years projected to be £11.9 million.

Given the seriousness of human VTEC infection, the lack of therapeutic options and the apparent lack of control measures for the animal reservoir, blocking transmission pathways is essential for reducing the morbidity and mortality from this serious disease.

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