Chlamydia is the most common sexually transmitted infection. Between 2001 and 2002 there was a 14 per cent rise in the number of cases of chlamydia diagnosed at genito-urinary clinics - a rise of 15 per cent in men and 13 per cent in women.

The number of cases has risen steadily since the mid 1990s and more than doubled from around 34,100 cases diagnosed in 1996 to just under 81,700 in 2002.

The highest rates are seen in young people, especially women under 25 years. In 2002, 16 to 19 year old females had the highest chlamydia rate, at 1,201 per 100,000 females seen at clinics - a diagnostic rate equivalent to almost 1 per cent of the female population within this age group. Among men the highest rate was for those aged 20 to 24, at 837 per 100,000.

In 2002, within England, rates in both males and females were highest in London, but were also high in Yorkshire and Humberside and the North West.

Genital chlamydial infection is an important reproductive health problem, because 10 to 30 per cent of infected women develop pelvic inflammatory disease (PID).

In 2002 the second most common sexually transmitted infection was uncomplicated gonorrhoea. There were 24,953 infections diagnosed in genito-urinary clinics in 2002, a 9 per cent increase from 2001. Again young people are most commonly infected and the highest rates are found in London and predominantly urban areas.