Tuberculosis Contact Investigation and DNA Fingerprint Surveillance in The Netherlands: 6 Years' Experience with Nation-wide Cluster Feedback and Cluster Monitoring

Setting: The Netherlands, 1995-2000.

Objectives: To describe the contribution of 6 years of nationwide DNA fingerprint surveillance to tuberculosis control in general and to conventional contact investigations in particular.

Design: All Mycobacterium tuberculosis cultures are subjected to standardised IS6110-based RFLP typing, and clustered cases are systematically reported to the regional TB services involved (cluster feedback). Standardised questionnaires are used to collect information on contact investigations and epidemiological links (epi links) at regional level. Revision of the questionnaires for the period 1997-2000 allows comparison of epi linking before and after cluster feedback.

Results: Among 2206 clustered cases, 462 (21%) epi links were expected before the RFLP result, whereas an additional 540 (24%) epi links were established after cluster feedback. Epi links based on documented exposure increased by 35%, from 357 to 550 (P < 0.001). Only 1% of contact investigations were extended, however, and relatively few additional persons with active or latent tuberculosis were diagnosed. Reasons for the limited impact on contact investigation outcome were 1) contact took place 1-7 years previously (51%), 2) documented contact involved a subsequent case in the cluster (21%), 3) casual contact (15.5%) and 4) different region (9%). Five per cent of epi links established by contact investigation were contradicted by RFLP data. Epi links were more frequently documented in Dutch (41%) than non-Dutch cases (19%, OR 3.0; 95%CI 1.41-1.91). Cluster monitoring permitted: 1) identification of transmission chains that could not be detected by contact investigations, 2) development and evaluation of targeted interventions, and 3) identification of professional failures and poor programme performance.

Conclusions: RFLP surveillance forms the bridge between conventional contact investigation and other forms of targeted active case finding. Combining both complementary strategies in a comprehensive approach to systematic outbreak monitoring and management allows countries in the elimination phase of the disease to better target and evaluate TB control interventions.