Tuberculosis contact investigation following the stone-in-the-pond principle in the Netherlands-Did adjusted guidelines improve efficiency?

Background: In low tuberculosis (TB) incidence coun-tries, contact investigation (CI) requires not missing contacts with TB infection or disease without unnec-essarily evaluating non-infected contacts. Aim: We assessed whether updated guidelines for the stone-in-the-pond principle and their promotion improved CI practices. Methods: This retrospective study used sur-veillance data to compare CI outcomes before (2011-2013) and after (2014-2016) the guideline update and promotion. Using negative binomial regression and logistic regression models, we compared the number of contacts invited for CI per index patient, the num-ber of CI scaled-up according to the stone-in-the-pond principle, the TB and latent TB infection (LTBI) testing coverage, and yield. Results: Pre and post update, 1,703 and 1,489 index patients were reported, 27,187 and 21,056 contacts were eligible for CI, 86% and 89% were tested for TB, and 0.70% and 0.73% were iden-tified with active TB, respectively. Post update, the number of casual contacts invited per index patient decreased statistically significantly (RR = 0.88; 95% CI: 0.79-0.98), TB testing coverage increased (OR = 1.4; 95% CI: 1.2-1.7), and TB yield increased (OR = 2.0; 95% CI: 1.0-3.9). The total LTBI yield increased from 8.8% to 9.8%, with statistically significant increases for casual (OR = 1.2; 95% CI: 1.0-1.5) and community contacts (OR = 2.0; 95% CI: 1.6-3.2). The proportion of CIs appropriately scaled-up to community contacts increased statistically significantly (RR = 1.8; 95% CI: 1.3-2.6). Conclusion: This study shows that pro-moting evidence-based CI guidelines strengthen the efficiency of CIs without jeopardising effectiveness. These findings support CI is an effective TB elimina-tion intervention.