E. coli is a leading cause of food poisoning
Stomach bugs picked up during foreign travel may be prevented by wearing a patch impregnated by toxins produced by the E. coli bacterium.
US research published in the Lancet medical journal found the patch was 75% effective against diarrhoea attacks caused by E. coli among volunteers.
Patch-wearers who did fall ill recovered far more quickly, it said.
A UK travel medicine specialist stressed only 40% of diarrhoea cases were caused by E. coli.
Stomach upsets are commonplace among people travelling to certain parts of the world, and the symptoms - vomiting, diarrhoea and stomach cramps, can often leave people incapacitated or weak for days.
The study authors, who work a biotech company IOMAI in Maryland, estimated that they affect up to 27 million travellers each year.
Their patch contains the poisons produced by E.coli, with the idea that this primes the immune system to cope better when confronted with the real thing.
Their study involved 178 people who were given either a placebo 'dummy' patch, or one containing the toxin, then sent off to continue their journey through Mexico or Guatemala.
A fifth of those with the "dummy" patches developed moderate diarrhoea, four times more than in the treated group. The difference was even more pronounced in cases of severe diarrhoea.
Even when someone with an E.coli patch fell ill, they got better quicker - half a day compared with two days on average.
They wrote: "This study suggests that transcutaneous immunisation with LT in a patch could protect travellers against this common, debilitating ailment."
Dr Richard Dawood, who runs a specialist travel health clinic in London, said the effects of the patch were similar to those produced by a vaccination against cholera, which, as a side effect, offers some protection against E. coli.
He said: "E.coli causes an estimated 40% of all travellers' diarrhoea, so this does not offer complete protection.
"However, if you are travelling abroad for commercial reasons, or with the military, it may be worthwhile paying for this sort of treatment.
"If you've paid several thousand pounds to take your family on holiday abroad, every day lost is worth hundreds of pounds, so it could be an advantage here, too."