Background DNA amplification assays are increasingly being used to facilitate the testing of asymptomatic individuals for urogenital Chlamydia trachomatis. The long-term clinical benefit in terms of avoided infertility and ectopic pregnancy is unknown.

Methods In 1997, 15 459 women and 14 980 men aged 21–23 years were living in Aarhus County, Denmark. A random sample of 4000 women and 5000 men was contacted by mail and offered the opportunity to be tested for C trachomatis by means of a sample obtained at home and mailed directly to the laboratory. The remaining 11 459 women and 9980 men received usual care and constituted the control population. All men and women were subsequently followed for 9 years by the use of Danish health registers. Data were collected on pelvic inflammatory disease (PID), ectopic pregnancy (EP), infertility diagnoses, in-vitro fertilisation (IVF) treatment and births in women, and on epididymitis in men. The intervention and control groups were compared using Cox regression analyses and the intention-to-screen principle.

Results Among women, no differences were found between the intervention group and the control group: HR (95% CI) for PID 1.12 (0.70 to 1.79); EP 0.97 (0.63 to 1.51); infertility 0.87 (0.71 to 1.07); IVF treatment 0.88 (0.62 to 1.26) and births 1.02 (0.95 to 1.10). In men, the HR for epididymitis was 1.25 (0.70 to 2.24).

Conclusions A population-based offer to be tested for urogenital C trachomatis infection by the use of non-invasive samples and DNA amplification did not reduce the long-term risk of reproductive complications in women or of epididymitis in men.

Trial registration number in www.clinicaltrials.gov NCT 00827970.