Sexual health: The chlamydia crisis

Twenty-year-old William Forest, a student at the University of Durham, admits he didn't know how to deal with it when he found he had the infection.

"When she told me, it threw me. It is something that you don't think will ever happen to you," he says. "When the test came back positive I was out of kilter for a few days. But I didn't feel too bad as I knew it could easily be treated."

Chlamydia is now the most common sexually transmitted infection (STI) in the UK, affecting more than 100,000 people a year, according to sexual health charity Brook. The infection is particularly prevalent among young people, with nearly one in nine under-25s testing positive for it under a government national screening programme. If left untreated the infection can affect the genitals, urethra and rectum of men and women, and also the throat and eyes. In severe cases it can spread to other reproductive organs, causing serious long-term consequences such as pelvic inflammatory disease, ectopic pregnancy and infertility.