The POPI (prevention of pelvic infection) trial has found that screening sexually active young women for chlamydia infection and treating those found to be infected reduced the incidence of pelvic inflammatory disease (PID) in the 12 months that followed.

Sexually active women under 27 were eligible for the study. Women were excluded if they had been tested for chlamydia infection in the past three months or were pregnant. Women were recruited in bars, common rooms, lecture theatres in some London universities and further education colleges.

Participants were informed about chlamydia infection and its risks.

They were asked:

• about their sexual health using a questionnaire
• to provide a self-taken vaginal sample
• to allow access to their medical records with a follow-up after a year.

Within two weeks of recruitment, the sealed sample packs with completed unopened questionnaires and consent forms were randomly assigned to two groups.

The intervention group had their vaginal samples tested for chlamydia; the samples that were allocated to deferred testing had the swabs stored at -800C and analysed a year later.

Women found to be infected were contacted within two weeks of diagnosis and asked to attend a sexual health clinic or their GP for treatment and partner notification.

A year after recruitment, the participants were asked to complete a secure on-line questionnaire related to possible symptoms of PID:

• pelvic pain
• dyspareunia
• intermenstrual bleeding
• abnormal vaginal discharge

and sexual behaviour during the past year.

Women who reported PID symptoms on the questionnaire had their symptoms verified using medical records from their GP, GUM clinic or other health service providers such as hospitals and family planning clinics.

The anonymised data were analysed by three GUM consultants who were blinded to allocation for diagnosis of PID, using agreed diagnostic criteria.

Baseline prevalence of chlamydia was 5.4% in screened women and 5.9% in controls. After follow up, the incidence of PID was 1.3% in screened women and 1.9% in controls, relative risk 0.65 (95% CI: 0.34-1.22). In the control group, 9.5% of women who tested positive for chlamydia at baseline developed PID 12 months later, compared with 1.6% of screened women. Relative risk 0.17 (95% CI: 0.03-1.01).

Most episodes of PID occurred in women who tested negative for chlamydia at baseline.

The authors conclude that while there is some evidence to suggest that  screening for chlamydia infection reduces rates of PID especially for women diagnosed with chlamydia at baseline, a single test for chlamydia cannot be assumed to prevent a case of PID over 12 months.

The authors suggest repeat screening might be warranted for women who may be considered to be at higher risk, e.g. those with a new sexual partner, or a recent history of chlamydia infection.

The National Chlamydia Screening Programme has been progressively rolled out across England from 2003. This screening programme has been set up to reduce transmission and reproductive tract morbidity. There remains controversy about the evidence base. The results of a landmark trial of chlamydia screening to prevent PID have been questioned; more recent randomised trials have not been conclusive.

This study aimed to overcome many problems that affected previous studies such as quality of randomisation, allocation concealment and blinding of assessment of outcome.

While the POPI study does not prove beyond doubt the effectiveness of a chlamydia screening programme, it does prove there is some evidence that it can reduce incidence of PID.

Also of interest is that it helps clinicians not to dismiss taking a sexual history in a woman who has had a chlamydia test as she might have been exposed to risks since the last test.

Dr Richard Ma

• Oakshott P, Kerry S, Aghaizu A et al. Randomised controlled trial for screening for chlamydia trachomatis to prevent pelvic inflammatory disease: the POPI (prevention of pelvic infection) trial. BMJ 2010; 340: 1642