Cornish health officials are asking for anyone who believes they may be at risk after a number of HIV cases were diagnosed to come forward for testing.
Modern drugs can slow down the effects of the virus
It follows news on Friday that a number of people have tested positive for the virus in St Ives.
A helpline (0845 850 9850) is operating for those worried they may be infected.
Dr David Miles, the director of public health, said the people affected were heterosexual men and women with an age range of between 20 and mid-50s.
The special telephone hotline has been set up by the West of Cornwall Primary Care Trust for people who are worried they may have the virus.
Additional testing facilities are also being set up in the area.
Dr Miles said it was a matter of concern that the trust has been unable to trace the sexual partners of fewer than 10 people.
"We've not been able to trace contacts and people's recollections may not be accurate," he said.
"We hope there aren't any more people who've contracted HIV in the West Cornwall area, however we think it's quite possible there may be."
He said there were "some links to a person" but patient confidentiality meant details could not be disclosed.
The PCT said the cases, some of which are recent and others which go back eight years, came to light within the past month.
Dr Miles said he could not be more specific about the exact number of cases or how they were detected, again because of confidentiality.
Kernow Positive Support, a group set up to help people who have HIV, said the PCT press conference and related media coverage was a mixed blessing.
A spokesperson said it was good because it highlighted the risks to everyone, but it could also scare people unduly.
The Terrence Higgins Trust said the most important thing was for people not to panic.
Spokeswoman Sally Wright told BBC News: "I think it's great the trust have set up the helpline and extra testing facilities.
"It's always a concern, but I'd urge people not to panic. They should call either the emergency helpline, or they could contact us.
"Even if they've had unprotected sex, the odds of contracting HIV are still very low."
Local MP Andrew George said people should be reminded that threat of HIV Aids has never gone away.
Mr George told BBC News: "I think it's important that people are given a timely reminder, particularly vulnerable groups who are at risk, that they need to take precautions."
Teresa Timms from Cornwall Tourism believes the incident is unlikely to deter holidaymakers coming to the area.
She said: "St Ives is one of the most popular and beautiful resorts in Cornwall, so we don't think people will stay away.
"But we hope it acts as a reminder that unprotected sex is not a good idea."
The HIV virus damages the immune system which is the body's defence against disease.
There is no cure, but modern drugs can now slow down the effects of the virus.