A lover's betrayal cannot be much more shocking and damaging than inflicting a terminal disease on a partner.

Alex, 31, thought he was in a loving, trusting relationship until a routine medical check-up for a new job revealed he was HIV positive.

He had recently broken up with his partner but had believed the pair had shared all their secrets.

He said: "He told me he was clean and I knew I was so we did not take any protection. It was an incredible setback.

"I knew all about the warnings and thought it was safe but it shows you have got to be 100 per cent careful."

He is one of hundreds of people in Brighton and Hove receiving treatment for HIV - a figure rising each year.

More people than ever are becoming infected - and more are dying.

There are fears limited medical breakthroughs have allowed people to become complacent about protecting themselves against the risks.

Brighton and Hove has the largest number and concentration of cases in Sussex. There were 747 people living with HIV in 2002 compared with 639 in 2001.

Numbers have increased by 84 per cent since 1997.

There were 94 new cases diagnosed in Brighton in 2002 and 82 in the first nine months of this year.

Charities and medics admit the actual figure is probably much higher because there are probably large numbers of people who are infected but don't know it yet.

Between 2001 and 2002, the numbers attending the clinic at the Royal Sussex County Hospital, Brighton, for HIV testing have risen by 34 per cent to 5,500.

Gay men are still the most at-risk group in the city, making up 82 per cent of cases with the second highest, heterosexual sex, accounting for eight per cent.

Andrew Hanuman, 37, was diagnosed eight years ago. He is a health promotion worker at the Open Door Project in Kemp Town and helped oversee the publication of T-Cell Chronicles, a book written by people with HIV who have shared experiences of their illnesses.

He is a great believer in the power of positive thought and prefers to think about living with HIV rather than dying from it.

Alex said: "I just take each day as it comes and get on with my life. I can't keep on thinking about something like this hanging over me.

"I have a lot of friends and a good social life and try not to let the virus dictate everything I do."

But, with a guaranteed long-term cure for the condition still a long way off, health chiefs are alarmed by the rising infection rates.

Brighton and Hove's 20,000-strong gay male community is a priority target group for Brighton and Hove City Primary Care Trust's plans to tackle HIV.

Paul Martin, the trust's sexual health and health development manager, said: "The increase in numbers being treated is not unexpected but there are concerns. It is a good sign because it shows people are responding well to treatment and are living longer but this increase in services provided is not matched with an increase in funding from the Government.

"The increases tend to be a couple of years behind, which can increase pressures."

The trust is focusing its attention on "at-risk" groups, including gay men, sex workers, the homeless and young people.

It has seen an increase in cases among ethnic minorities and is targeting this group too.

Mr Martin said: "There has been anecdotal evidence some people are assuming HIV is not as serious as it was and are not taking the right precautions.

"This is leading to numbers going up but we have not seen any evidence of that. As far as we have found, people are well aware of the dangers and it is still one of their main concerns. Treatments may mean people are living longer with HIV but the long-term focus is to reduce the number of new infections recorded each year."

The increase in Brighton and Hove is in line with national figures published by the Health Protection Agency. These show there has been almost a 20 per cent increase in the number of people living with HIV in the UK, up from 41,700 in 2001 to 49,500 in 2002.

Globally, five million people became infected with HIV this year and three million died - the highest total ever recorded.

An estimated 40 million people around the world are infected with HIV, including 2.5 million children under the age of 15.

Dr Kevin Fenton, a HIV public health consultant at the agency, said: "World Aids Day reminds us the problems we face with HIV are not going away, despite it being a disease that is largely preventable.

"The group most at risk of contracting HIV in the UK remains gay and bisexual men, accounting for about 80 per cent of new diagnoses in 2002.

"With stigma and discrimination being the theme for this year's World Day, it is important to highlight these are still major obstacles for people living with HIV.

"Tackling these issues is important so more people may come forward for testing. The earlier people are diagnosed with HIV, the greater chance they have of living a longer and healthier life.

"Awareness of their HIV status also enables people to make choices about their sexual behaviour and practising safer sex."