The crude police-style body outline daubed on the road behind the harbour is accompanied by a piece of scrawled, ungrammatical advice. "Should of worn a condom," the graffiti reads.

St Ives, one of England's most beautiful seaside resorts, is struggling with the disturbing realisation that it has a major HIV outbreak in its midst. While graffiti can quickly be covered up, the Cornish community's anxiety is less easily concealed.

On Monday, the first results of the HIV tests, undertaken after health officials announced they had uncovered up to 10 cases in the town, will be known.

With the source of the biggest heterosexual outbreak in Britain for 10 years still a mystery, the tests could provide a break-through in establishing his or her identity. So far more than 200 people have called the dedicated helpline to arrange tests.

In such a small community - St Ives' population is 6,000 - rumours are rife. "That's the name that's being spread around," confided one shopkeeper to a customer, before swiftly adding: "But it's not fair to gossip."

Martin Page, who moved to St Ives 30 years ago, said the impact on the lives of people in the town could not be underestimated. "The chances are that whoever is involved will not want to stay here," he said. "Some people will be having HIV tests done in Plymouth because they do not even want people to know. People have not changed their behaviour here since the late Seventies and the place has always had a bohemian atmosphere."

St Ives has attracted a thriving artistic community for decades as well as a more traditional holiday crowd. But it retains its sense of identity as a community.

Sonia Pacey, sales assistant at the Wind and Sea Surfing Centre, said that the scare was frightening because St Ives is such a small place. "I have heard rumours that it is one man, and, if it was that person, everybody would be very annoyed," she said.

Jonny Dex, 26, manager of the Iso Bar, St Ives' only nightclub, said: "Because St Ives has a small population, there are likely to be more people who have shared the same sexual partners."

More than 70 people in Cornwall are being treated for HIV and Aids. In 2004, there were 49 new cases in Devon and Cornwall combined. An Ipsos MORI poll, commissioned by the National Aids helpline last year, found that, nationwide, people were less aware of how HIV was transmitted than five years ago. More than one in five people now claim HIV cannot be caught through heterosexual sex - twice as many as five years ago.

Dr David Miles, director of public health for the West of Cornwall Primary Care Trust, said that the announcement that people who had had unprotected sex in St Ives should be tested for HIV was prompted by a growing number of people testing positive for HIV. He said: "We had become aware of a number of cases in the last month and knew we could not trace all contacts. The best way to deal with the problem was to let everyone know at the same time. We think that people have been at risk for the last eight years up until the present time, and there are some links between the cases."

In the Sheaf of Wheat pub, friends Scott Rowe and Kerry Trevorrorw, both 18, were discussing the scare. Ms Trevorrorw said: "People think the Pill protects them from sexually transmitted infections, and it doesn't. And they think that they are protected because it is such a small town." Mr Rowe said: "I know I have been safe where possible but I am going to get tested. If there's the risk there, I would rather address it and have peace of mind."

Rose Hitchens, 17, a sales assistant at Just Toys on Lifeboat Hill, has just returned to St Ives from Swaziland, where she worked with HIV orphans, to find the same virus in everyone's minds. She said: "Having just seen the scale of the HIV problem in Africa, it is a shock to find the issue on my doorstep here in St Ives. People have become a bit complacent but this is a worldwide issue no one can ignore."

Virus facts

* A total of 58,000 people in the UK are HIV positive, but a third of infections are believed to be undiagnosed, according to the National Aids Trust.

* In 2005, 6,727 people were diagnosed with HIV in the UK. Of these, 53 per cent (3,550) acquired the virus through heterosexual contact, 30 per cent (2,039) through sex between men, and 1.6 per cent (106) through injecting drugs.

* More than 40 million people are living with HIV across the world. Sixty per cent of all HIV cases are in sub-Saharan Africa. There were almost five million cases of HIV diagnosed worldwide in 2005 and more than three million deaths from Aids in 2005.