Newly released figures from the Health Protection Agency (HPA) show a worrisome increase in STDs in the United Kingdom. Sexual health clinics in 2009 reported 482,700 new STD cases - 12,000 more than in the previous year.

The data clearly show that people under age 25, particularly females, are most affected by STDs. Dr. Gwenda Hughes, head of the STD section of HPA, said two-thirds of diagnoses were in females ages 15-24. The peak age for STD infection in young women is 19-20, compared to 20-23 for men. And roughly 10 percent of the 15- to 24-year-olds who are treated for an STD will be re-infected within a year.

Though improved screening efforts are behind some of the increase, experts say they are concerned about youths who are vulnerable and lack confidence to negotiate safe sex. Many studies show that young people often lack the skills to negotiate safer sex in their relationships.

"The numbers we're seeing in teenagers are of particular concern as this suggests they are repeatedly putting their own as well as others' long-term health at risk from [STDs]," said Hughes.

According to the data, STD diagnoses were also high among men who have sex with men.

HPA said genital wart and syphilis diagnoses have stabilized, but gonorrhea is on the rise. Of particular concern is that resistance to the main antibiotic used to treat gonorrhea, cefixime, rose from 0.1 percent in 2005 to 10.6 percent last year. HPA's gonorrhea expert, professor Cathy Ison, said no new antibiotics are in the pipeline to treat the infection. Cefixime may be effective against gonorrhea for only another five years, she estimated.