Page 40 - Epidemiological studies on tuberculosis control and respiratory viruses

Chapter 7
General Discussion
In most of the tuberculosis (TB) low-incidence countries overall notification rates for TB have been declining for the last decades. Also in the Netherlands, with a total incidence of 5.1 cases per 100,000 population reported in 2013, TB has become a rare disease (1). In order to further reduce transmission rates and reach TB elimination (defined as TB incidence <1 case per million persons per year) in low-incidence countries, the WHO developed a global framework to reach these goals (2). One of the priority actions defined in this framework is to “undertake screening for active tuberculosis and latent infection in tuberculosis contacts and selected high-risk groups and provide appropriate treatment.” To effectively reach this target in each country, tailored actions, depending on country-specific conditions, are required. In this thesis various aspects of epidemiological and health system conditions in the Netherlands were investigated. Here we discuss the implications of our findings, and provide recommendations for further actions and research to improve TB control in the Netherlands, and in other low-incidence countries with comparable conditions.
Recent transmission and foreign M. tuberculosis strain lineages
As TB incidence in the Netherlands is declining, TB elimination efforts are mainly focussed on specific high-risk groups such as the foreign-born. Rapid and accurate identification of recent transmission events is important to stop transmission chains. Clustering of M. tuberculosis isolates from cases with identical DNA fingerprints can be used as a proxy for recent transmission and has been a successful tool in public health to identify previously unknown transmission routes and factors associated with a higher risk of transmission (3) (4). DNA fingerprinting should therefore be used as routine surveillance to identify unexpected spread of TB and outbreaks, and to evaluate interventions (5). However, clustering as a proxy for recent transmission is not always correct, and should be interpreted with caution, especially among foreign-born cases, as isolates obtained from these patients might belong to genetically homogenous strain lineages predominating in their countries of origin. In the Netherlands, 24-locus Variable Number of Tandem Repeat (VNTR) typing was introduced in 2004, and became the new standard for DNA typing in 2009. In chapter 2 we studied the associations between VNTR genotypes of causative M. tuberculosis strains and their human host populations.
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