Doctors are advising football fans who went to the World Cup in South Africa to check their HIV status if they had unprotected sex on their trip.
Up to 25,000 England fans recently returned from South Africa, where about six million people have HIV.
More than two-thirds of heterosexual men and a quarter of women with HIV have contracted it abroad.
An awareness campaign is urging those who may have put themselves at risk to visit their local sexual health clinic.
The campaign - 'Beer Goggle Johnny's Guide to Sexual Health' - has been launched by Birmingham's Heartlands Hospital, but is backed by national organisations.
Dr Steve Taylor, sexual health and HIV consultant at Heartlands Hospital, said nearly one in five young adults living in South Africa were infected with the virus, and in some areas it could be as high as one in three.
"During the festivities if holiday makers had unprotected sex it is more important than ever to get themselves checked out on their return," he said.
"Although the public are more aware of the dangers of unsafe sex these days, we are not seeing people putting this into practice, which is worrying.
"It's while on holiday, as people relax, soak in the sun and consume alcohol, the chance of having unprotected sex is increased.
"We want holiday makers to take precautions, pack condoms in their suitcase and attend sexual health screenings on their return if they are unsure."
He added: "The only way we can help prevent widespread infection of STIs (sexually transmitted infections) in this country is through early testing, and treating infections before they can spread - and when they are easier to treat.
"Even HIV, for so long a virus to dread, can be managed very effectively if detected in its early stages."
The Beer Goggle Johnny campaign began as a local initiative, but the national roll-out is being backed by organisations including the Terrence Higgins Trust and the British Association for Sexual Health and HIV (BASHH).
As well as a website promoting the Beer Goggle Johnny campaign Heartlands are offering to customise posters for clinics around the UK using the same characters and information alongside local information about clinics and advice.
Peter Greenhouse of BASHH said it strongly supported the "amusing and engaging" campaign.
"There's always a sharp increase in STI cases after the summer holidays," he said.
"With 25,000 football supporters returning from South Africa, and many more about to go away for the summer, it's a great move to get a check-up when you return and to use condoms when you're away.
"People are most likely to infect others with HIV just after they've been infected themselves, just after they come home - so Beer Goggles Johnny could be a lifesaver."