Cases of sexually-transmitted diseases have soared in Sussex, figures showed today.

There were 8,559 diagnoses in 2002 by Surrey and Sussex Strategic Health Authority compared with 5,198 in 1997, a 64.6 per cent increase.

The statistics, published by the Department of Health, covered diseases including herpes, syphilis, gonorrhea and chlamydia. HIV was not included.

Richard Forshaw, of Brighton and Hove City Primary Care Trust, said the rise was most acute for 15 to 24-year-olds.

He said: "It's a trend we have been tracking. It's about people's lifestyle and behaviour and about people getting better at finding out about conditions and treatment.

"People are more sexually active than they were. People are also more content to visit their GP than before."

Surrey and Sussex had the sixth highest increase in STDs in the five-year period. South-west London had the biggest increase, of 105.3 per cent, from 3,824 to 7,853.

Doctors said people were becoming complacent about STDs, especially after strong messages about safe sex sparked a decline in infection rates during the 1990s.

Mr Forshaw said the trust had been trying to reverse the trend. He said: "We are working across the board with charities, schools and the council and developing new services like outreach work.

"We have to work very hard to get people to change their lifestyle but it takes time. There might well be the problem that everyone thinks they're safe. These things can make you very ill and extremely uncomfortable. People need to be aware of the symptoms and they need to practice safe sex."

Rod Watson, regional manager for the Terrence Higgins Trust South, which works particularly with gay men, said he was worried about the general rise in STDs. Mr Watson said: "We would encourage sexually-active gay men to go and get tested. Those with a large number of partners should really be tested once every three to six months.

"Syphilis has been a particular problem as it is easily contracted."

There needed to be more investment in STD screening and prevention.

He said: "We need more testing and better availability."