The number of sexually transmitted infections diagnosed in UK clinics has continued to rise, latest figures show.
Other STIs have gone up, but cases of gonorrhoea have gone down
The Health Protection Agency data show a 2% increase overall from 735,302 cases in 2003 to 751,282 last year.
The biggest rise was recorded in the number of syphilis cases - up 37% to 2,252 cases last year.
Cases of chlamydia - the most common sexually transmitted infection in the UK - also rose by 8% to a total of 103,932 cases in 2004
But gonorrhoea cases fell by 10% to 22,320.
Experts said the continuing rise, particularly among younger age groups, was extremely disturbing.
Jan Barlow, chief executive of Brook, the sexual health charity for young people, said the figures were "extremely disturbing".
"Our own research shows that there are still serious gaps in young people's knowledge of STIs. More than half believe that men can't get chlamydia and almost a third think you can catch an STI from a toilet seat.
"Even when young people understand the theoretical risk of STIs, they regard them as something that happens to other people.
She said guaranteed sex and relationships education backed up by a high profile awareness campaign targeting young people would be the most effective ways of tackling the problem.
Anne Weyman, chief executive of the Family Planning Association, also thought sex and relationship education in schools should be mandatory.
She also thought more efforts were needed to ease workload pressures on clinics.
However, she said the apparent rise might be down to better detection.
NUMBER OF STIs DIAGNOSED BETWEEN 2003 & 2004
Chlamydia up by 8% (from 95,879 to 103,932)
Syphilis up by 37% (from 1,641 to 2,252)
Genital warts up by 4% (from 76,457 to 79,618)
Genital herpes down 1% (from 19,180 to 18,923)
Gonorrhoea down 10% (from 24,915 to 22,320)
"An increase in STI rates is always a matter of concern. However, we would expect there to be an increase in people coming forward for diagnosis and treatment. It is encouraging that rates of gonorrhoea and genital herpes are showing a decline," she said.
Dr Helen Ward, an STI expert at the HPA's Centre for Infections, said: "A further rise is disappointing but some encouragement can be taken from the slower growth seen in recent years and in some areas new diagnoses have fallen."
But she added: "We cannot be complacent.
"There were over 103,000 new diagnoses of chlamydia in 2004, an 8% increase from 2003. Young people are at particular risk.
"Infectious syphilis continues to increase...most rapidly in women and heterosexual men."
Baroness Gould, chair of the Independent Advisory Group on Sexual Health and HIV, said: "These figures are an indicator that the work the government has put into action to tackle sexually transmitted infections must be continued, supplemented and supported."
Nick Partridge, chief executive of Terrence Higgins Trust, said: "This illustrates the vital importance of primary care trusts using the money the government has given them for sexual health appropriately."
Doctors at the British Medical Association conference in Manchester called for improvements in sexual health services, including more funding and a campaign to improve awareness.
Conservative Shadow Health Minister Simon Burns said the figures were proof that current government initiatives on sexual health were failing.