Unpacking chlamydia screening coverage in England, including estimates of partner notification and repeat testing outcomes

Introduction The number of chlamydia tests performed amongst the target age-group (<25 years) for screening in England has increased markedly over the last decade. Evaluation of this national screening programme is enhanced by understanding the relationship between testing coverage and rates of diagnosis, repeat testing, partner notification (PN) and positivity. Our data sources allow some examination of these relationships. Methods To the end of 2013, chlamydia tests and diagnoses in England were captured in two national surveillance systems, with tests reported by testing venues (STD clinics) and laboratories (other settings). Records were matched to remove duplicate testing episodes within 6 weeks and to estimate frequency of repeat testing. New surveillance codes were introduced to allow further de-duplication between surveillance systems and to monitor testing of partners. Results Approximately 13% of diagnoses were excluded from total chlamydia diagnosis counts as probable duplicates. Estimated coverage (tests/population) amongst 15-24 year-old women was 35% of the total population (44% among sexually-active women) nationally. Positivity varied by setting and coverage. 47% of diagnoses were made in STD clinics. 13% of young women tested in STD clinics and 10% tested in other settings had >1 test within 1 year; re-testing rates were higher following a positive rather than a negative test. In STD clinics, 0.6 heterosexual male partners were seen per woman diagnosed with chlamydia; positivity amongst male partners was 37%. Conclusion Detailed monitoring of chlamydia screening activity is available in England, although there are limitations. Our data suggest re-testing of positives and PN make important contributions to coverage and diagnoses.  Further developments to improve accuracy of testing information and PN effectiveness are underway. While we continue to monitor coverage, England now focuses on the diagnostic rate per 100,000 as the outcome measure of screening activity, as coverage alone does not capture chlamydia control activity.