Background Systematic screening for Chlamydia trachomatis (Ct) by individual invites ensures general reach, but is less (cost) effective, as it includes people at no or low risk. Selective systematic screening can overcome this. In a large-scale Chlamydia Screening programme in the Netherlands selection by risk score was applied in one region where relatively low prevalence was expected. Here we show the effect of selection on participation, positivity and acceptability in three srceening rounds.
Methods Invitees were alerted by personal letter to login to http://www.chlamydiatest.nl/ and fill in an 8-item questionnaire before a test could be requested. Questions, based on a prediction rule assessed in a pilot, addressed age, place of residence, education, ethnicity, symptoms, condom use and sex partners. Answers yielded different points accumulating in a risk score. Only invitees with sufficient score of 6 or more could proceed and receive a testkit. Mailed samples were tested at a regional laboratory with NAAT. A sample of excluded participants received an acceptability questionnaire.
Results The selection led to exclusion of 36% of potential participants and a positivity rate of 4.8% among participants (see Abstract P5-S4.03 table 1 Women scored on average higher than men (6.6 with 95% CI 6.5 to 6.7 vs 5.8 with 95% CI 5.7 to 5.9, p<0.001). Higher scores were clearly related to higher positivity rates. Persons who were excluded from participation in the first year because of a low risk score had a significantly lower response to the invitation the second round (21% vs 29%, p<0.01). The acceptability questionnaire among excluded participants (n=67, response 34%) revealed disappointment about exclusion in 30% of them but most approved of the screening set-up; 8% still went to a GP or STI centre for a Ct test.
Conclusions Systematic selection of screening participants by risk score in Chlamydia screening is feasible and successful in realising higher positivity rates than without selection. A previous study showed a population prevalence of 2% in the same population. Acceptability of selection is high but could still be improved by better communication on expectations.