A government health body issued the advice yesterday after it was revealed that eight of the 90,000 people who attended the festival last month had contracted the bug which killed 22 elderly people in an outbreak in Scotland last year.
The National Health Laboratories, investigating the Glastonbury outbreak, said yesterday that the eight were recovering well but the youngest victim, a two-year-old, remains in hospital with kidney problems.
A spokeswoman said that given the length of time since the festival they did not expect to see any further cases. E. coli symptoms take between three and seven days to appear and the festival finished three weeks ago.
The blame for the outbreak was being placed either on cow dung getting mixed with the mud that covered the festival and most of those attending it, or an unhygienic food stall.
Glastonbury's organisers said yesterday that the cows that graze the festival site would be tested for E. coli next week, but the source of the outbreak might never be found.
"It is an incredibly complicated investigation," said Professor Hugh Pennington, who led the inquiry into the Scottish outbreak. "Glastonbury is the only common factor, but did they get it from the environment or did they all eat at the same hamburger stall?"
Allison Lyon, spokeswoman for the National Health Laboratories, admitted that many of those who attended the festival may not have been able to distinguish E. coli from the normal after-effects of three days of hedonism at Glastonbury.
"It's a basic public health message," she said. "Good hygiene is paramount and you have to wash your hands when there's mud."
Sean Dunne of Mendip District Council, which grants the licence for the festival, said the outbreak was probably due to extraordinarily wet weather.
"Torrential rain caused the whole ground to liquefy," he said. "And people wouldn't normally frolic in cow dung."