Estimating Tuberculosis Burden and Reporting in Resource-limited Countries: a Capture-recapture Study in Iraq

Background: The global target for tuberculosis (TB) control set by the Millennium Development Goals is a decrease in TB incidence by 2015. Direct measurement of country-level TB incidence using population-based methods is impractical, emphasising the need for well-performing surveillance systems and, where these are not available, accurate quantification of incidence and under-reporting of TB.

Objective: To estimate TB incidence and TB under-reporting in Iraq in 2011.

Methods: Prospective longitudinal surveillance was established among all eligible public and private non-National TB Programme (NTP) providers in a random sample of eight of the 18 Iraqi governorates from May to July 2011. Record linkage with the NTP and three-source capture-recapture analysis of data were then conducted using log-linear modelling.

Results: A total of 1985 TB cases were identified after record linkage. The NTP registered 1677 patients (observed completeness 84%). The estimated total number of TB cases was 2460 (95%CI 2381-2553), with identified TB cases representing 81% (95%CI 69-89) after adjusting for sampling design. The estimated ratio of notified to incident cases was 69% (95%CI 58-76).

Conclusions: We estimate 14 500 TB cases in Iraq in 2011, of which 31% (95%CI 24-42) were unreported. TB surveillance needs to be strengthened to reduce under-reporting.