High-risk sexual behaviour is continuing unabated in the UK, driving the incidence of some sexually-transmitted infections up by as much as 10% since 2000, according to a new report by independent market analyst Datamonitor.

And it is overwhelmingly young people who are being affected: 66% of reported cases of chlamydia and 54% of reported cases of genital warts are from those in the 16-24 age bracket, according to the report.

However, the report notes that improved screening practices may be behind the increase, rather than a true rise in disease incidence.

That said, STIs remain a significant problem worldwide, with the World Health Organisation (WHO) estimating that as many as 340 million people contract a curable STI annually, according to Datamonitor infectious diseases analyst Dr Brigitte de Lima.

Chlamydia is the most common STI, with up to 100 million cases annually, followed by gonorrhea with 62 million and syphilis with 12 million respectively. Chlamydia is also the most common STI in the UK, with over 100,000 cases reported in 2004, according to the Health Protection Agency (HPA).

In addition, in some countries the causative agent of genital herpes, HSV-2, is thought to affect approximately one-fifth of the population, while members of the family of the human papillomavirus (HPV), the etiological agents of both genital warts and cervical cancer, are estimated to be prevalent in around 10% of the population, causing over 500,000 annual cases of cervical cancer.

Vaccines the answer?

Past efforts to develop vaccines to prevent chlamydia and gonorrhea have met with little success, notes Datamonitor, but it notes the development of vaccines against HSV-2 and HPV infection as particularly encouraging. Three vaccines have reached Phase III clinical trials, including Merck& Cos Gardasil and GlaxoSmithKline’s Cervarix for HPV, and GSK’s Simplirix for HSV-2, according to Dr de Lima.

Gardasil received FDA fast-track review in February 2006, with launch expected later in the same year.

Datamonitor estimates that the total market potential for HPV vaccines in the seven major markets is around $3.7 billion, as there is likely to be a large pool of adult women who will want to receive vaccination. But sales are likely to drop to less than $670m after a few years, once use of the HPV vaccines becomes confined to mainly pre-adolescent patients, prior to the initiation of sexual activity.