Researchers have urged women to have a chlamydia test every time they have a new sexual partner, even if it was just a few months since their last test, because screening alone is unlikely to cut their chances of pelvic disease.

Experts from London hospitals set up a trial using 2,529 sexually active female students from 20 London universities and colleges with an average age of 21, and samples were either tested straight away or stored and tested 12 months later.

Of the women tested straight away, those found to have chlamydia were treated and all results were then checked against the number of women developing pelvic inflammatory disease over the next 12 months.

A total of 68 (5.4%) of 1,254 women screened immediately were found to have chlamydia, and 75 (5.9%) out of the 1,265 screened a year later also had it.

Fifteen (1.3%) of the women screened immediately went on to develop pelvic inflammatory disease, compared with 23 (1.9%) of those tested the following year.

Writing online in the British Medical Journal, the researchers said: “Although some evidence suggests that screening for chlamydia reduces rates of pelvic inflammatory disease, especially in women with chlamydial infection at baseline, the effectiveness of a single chlamydia test in preventing pelvic inflammatory disease over 12 months may have been overestimated.”