Background Register and internet-based Chlamydia Screening Implementation (CSI) was introduced in the Netherlands to detect and treat asymptomatic infections and to limit ongoing transmission through annual testing and treatment of Chlamydia trachomatis (Ct) in young people. This population-based screening may be compromised by addressing individuals who are already covered by regular care like general practitioners and STD clinics. We study, in a timeframe of five years, overlap between CSI participation and attendance of major services offering Ct screening services to assess whether CSI reached additional patients.

Methods Data included all Ct tests performed in subjects aged 16–29 years in Eastern South Limburg in the Netherlands (population 16–29 years: 42,000) between 2006 and 2010 by CSI, regional STD clinic, general practitioners (GPs), and specialists (mainly gynaecologists) as reported by the testing laboratory. Data were matched between testing agencies, with complete certainty (STD clinic) (name, date of birth) and with a certainty range (part of the name, month and year of birth). Maastricht University’s ethical committee approved the study. Analyses were restricted to subjects tested (at least) by CSI.

Results In CSI, 4477 (82.9%) subjects were first-time testers, others were previously tested by the STD clinic (3.5%, n = 190), GPs (6.4%, n = 352), specialists (3.6%, n = 197) or multiple providers (3.4%, n = 183). Compared to persons previously tested by the STD clinic/GPs/specialists, first time testers were younger (mean age 23y vs. 24y, p < 0.001), and more often were heterosexual men compared to women (29.8% vs. 13.6%, p < 0.001). Ct prevalence was similar in first time testers (4.6%) compared to previously tested persons (4.9%, p = 0.76). Symptom-rate was also similar (2.5% vs. 3.3% p = 0.32).

Conclusions Chlamydia screening addresses young individuals, including heterosexual men, hidden to current care with similar Ct prevalence and adds to the existing regular care.