• Chlamydia trachomatis
• pelvic inflammatory disease
• randomised control trial
• salpingitis
• mass screening

Andersen et al1 report findings from 9 years' follow-up in one county in Denmark of 30 000 men and women aged 21–23 years, of whom 9000 (4000 women and 5000 men) were randomly selected in 1997 to receive a mailed invitation to provide a self-obtained specimen for chlamydia screening. That study has exploited the rare opportunity offered by Danish health registers to link longitudinal health records for a cohort of young people, which included men (a rarity). Using an intention-to-treat analysis, the authors conclude that a single postal invite for chlamydia testing, with a repeat offer to those found positive, did not reduce the long-term risk of reproductive complications.1 What do these data add to the evidence base concerning the effectiveness of chlamydia screening? What lessons should inform further studies?

Previous randomised controlled trials (RCTs) of a single chlamydia screen, with 1-year follow-up for the incidence of pelvic inflammatory disease (PID), have noted the limitation of evaluating the impact of a single round of chlamydia screening, because the risk of chlamydia infection is ongoing,2 as should the intervention be.3 The study by Andersen et al1 with its long follow-up for ectopic pregnancy and infertility increases the probability of the acquisition of chlamydia infections after (or …