Completeness of TB notification in Portugal, 2015: an inventory and capture-recapture study

BACKGROUND: Despite the steady decline in the last few decades, Portugal remains the Western European country with the highest TB notification rates. The aim of this study was to estimate the completeness of notification to the National Tuberculosis Programme (NTP) Surveillance System (SVIG-TB) in 2015.METHODS: We implemented an inventory study and a three-source log-linear capture-recapture analysis using two additional data sources that were deterministic and probabilistically linked: the national notifiable diseases surveillance system (Sistema Nacional de Vigilância Epidemiológica SINAVE) and the national hospital discharge database (Grupos de Diagnósticos Homogéneos GDH).RESULTS: We identified 2328 unique probable/confirmed TB cases across the three data sources. We found a positive dependency between SVIG-TB and SINAVE (incidence rate ratio IRR 8.9, 95%CI 6.6-12.0) and between GDH and SINAVE (IRR 2.6, 95%CI 2.0-3.4). After adjusting for these dependencies, we estimated that 266 cases (95%CI 198-358) were not reported, indicating a notification (to SVIG-TB) completeness rate of 77.0%.CONCLUSION: True incidence rate of TB in Portugal in 2015 could have been as high as 26.1 per 100 000. This could be an overestimation because of false-positive cases recorded in both SINAVE and GDH or on a smaller scale, false non-matches. Studies aimed at validating potentially false-positive cases should be implemented to address these limitations.