Rob van Hest Capture-recapture Methods in Surveillance - RePub ...

Introduction
Underreporting of tuberculosis in the Piedmont Region, Italy
Meaningful quantification and description of the distribution of tuberculosis within a
community is an essential part of any tuberculosis control programme. 1,2 Underreporting
by local surveillance systems in countries with high and low endemicity for tuberculosis
leads to underestimation of the tuberculosis burden and makes descriptions and
interpretation of spatial and temporal variations unreliable. 3,4 In 2003, the World Health
Organization (WHO) estimated that underreporting of tuberculosis in Italy was 12% 5 but
according to other reports it reached 37-54% in some areas of the country. 6,7
Case detection can be improved by record-linkage, i.e. comparing patient data
across multiple registers, 6 and underreporting can be estimated by capture-recapture
analysis. The latter uses information after record-linkage of various datasets, evidenced by
the observed overlap of the registers, to estimate the number of cases unknown to all
sources. 8 Capture-recapture analysis was first used in studies of animal population biology
and, more recently, in epidemiology. 8-10 It is now increasingly used to estimate the burden
of both non-communicable11,12 and communicable diseases, 13,14 including tuberculosis.
4,15,16 We undertook record-linkage of multiple information systems and
subsequently conducted a capture-recapture analysis to estimate the tuberculosis
incidence in the Piedmont Region of Italy in 2001 and to assess the performance of the
surveillance system.
Study population and methods
Study population and case-definition
We focused the study on residents of the Piedmont Region, Italy, during 2001. According
to the fourteenth national census in 2001, the total resident population of the Piedmont
Region was 4 214 677, of whom 2 034 161 (48%) were men, 3 027 034 (72%) were age
< 60 years, 865 263 (20%) lived in Turin, the capital, and 84 070 (2%) were immigrants
from high tuberculosis burden countries (HTBCs), i.e. countries with an annual incidence
> 80 cases per 100 000 population. About one third of the immigrants were from North
Africa, one third from Eastern Europe or the former Soviet Union, and the remainder
came from Asia, sub-Saharan Africa and Latin America. 17
We included in the study all new cases of pulmonary tuberculosis and nonpulmonary
tuberculosis, diagnosed in the Piedmont Region in 2001 and known to at least
one of three tuberculosis registers. Tuberculosis cases were defined according to the
guidelines of WHO and the European Region of the International Union Against
Tuberculosis and Lung Disease Working Group for Uniform Reporting on Tuberculosis
Cases. 1,18 Cases were classified as follows: confirmed (culture-confirmed or smearpositive)
or probable cases (clinically, radiologically or empirically diagnosed); pulmonary
tuberculosis or non-pulmonary tuberculosis; patients < or ≥ 60 years; resident in the
Turin metropolitan area or in the remaining parts of Piedmont; and born in HTBCs or in
low tuberculosis burden countries (LTBCs), i.e. countries with an annual incidence < 80
cases/100 000 population. Cases caused by environmental mycobacteria (21 records)
were excluded to improve the specificity and the positive predictive value of each register.
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