Background: In the Netherlands, an Internet-based Chlamydia Screening Implementation was initiated in 3 regions, aiming to reduce population prevalence by annual testing and treatment of people aged 16 to 29 years. We studied who was reached in the first screening round by relating participation and chlamydia positivity to sociodemographic and sexual risk factors.
Methods: Data from the 2008/2009 screening round were analyzed (261,025 screening invitations, 41,638 participants). Participation rates were adjusted for the sexually active population. Sociodemographic and behavioral correlates of screening participation and positivity were studied by (multilevel) logistic regression models.
Results: The overall adjusted participation rate in the first screening round was 19.5% (95% confidence interval, 19.4–19.7) among sexually active people (women, 25%; men, 13%). Sociodemographic factors associated with lower participation were male gender (odds ratio [OR], male 1 vs. female 1.8), young age (OR, 16–19 1 vs. older groups 1.7–2.1), non-Dutch origin (OR between 0.7–0.9), lower education (OR, low 1 vs. high 1.4), high community risk level (0.8), and low socioeconomic status (0.9). Behavioral factors associated with lower participation were a long-standing relationship (0.7) and no reported history or symptoms of sexually transmitted infections (no symptoms, 0.4–0.6) . Factors most strongly related to higher Ct positivity were young age (OR, 1 vs. older groups 0.5–0.8), non-Dutch origin (1.4–2.8), non-Dutch steady partner (1.9–2.7), residence in a high-risk area (1.4–1.5), lower education (high, 0.3–0.5), and a history or symptoms of sexually transmitted infection (no symptoms, 0.4–0.6).
Conclusions: Sociodemographic factors associated with lower participation were also associated with higher Ct positivity, showing that high-risk demographic groups are more difficult to mobilize than low-risk groups. Independent of this, higher behavioral risk levels were associated with higher participation rates, suggesting self-selection for screening based on the persons' risk (perception) in both low- and high community risk groups. Our study shows the complexity of the process, including individual and community factors that also interact, when screening for chlamydia.