Prevalence of latent tuberculosis infection in immigrants in the Netherlands: screening using new tools
06 / 2008 - unknown
To determine the positive predictive value (PPV) of a positive interferon gamma release assay (IGRA) response at entry in the Netherlands for development of tuberculosis in immigrants originating from tuberculosis high incidence countries. The PPV will be used for cost-effectiveness studies and for policy recommendations to reduce the incidence of TB in recent immigrants in the Netherlands.Primary research questions:1. What is the prevalence of a positive IGRA response among a representative sample of immigrants who are eligible for chest X-ray screening at entry in the Netherlands?2. What is the incidence of TB disease within two years after mandatory chest X-ray screening among all immigrants eligible for chest X-ray screening? 3. What is the quantitative relation between the prevalence of positive interferon-gamma response and the registered incidence of TB disease within two years? Secondary research questions:1. What is the positive predictive value of a positive interferon-gamma response in relation, or in combination with, the positive predictive value of a positive tuberculin skin test?2. What is the quantitative relation between the prevalence of positive interferon-gamma response and published epidemiological data from the country of origin? The incidence of tuberculosis (TB) in the autochthonous Dutch population is decreasing. In immigrants TB remains a problem, in particular in the first years after entry in the Netherlands. Elimination of TB as a public health problem will not be possible without the implementation of interventions that reduce the incidence of TB in the migrant population. Chest X-ray screening of immigrants is currently applied but seems only cost- effective under specific conditions. Screening for tuberculosis infection and treatment of individuals with latent TB infection (LTBI) is a potential effective intervention. However, due to the low specificity of the currently applied tuberculin skin test it is difficult to identify individuals with tuberculosis infection. Therefore, the intervention is considered not cost-effective. Recently, new more specific tests for diagnosis of LTBI have become available. These interferon gamma release assays (IGRAs) may allow a more cost-effective screening of immigrants for LTBI at entry in the Netherlands. To assess whether this is a feasible strategy, we need to know what proportion of immigrants will test positive at entry and we need an estimate of the predictive value of a positive test result for development of TB within two years after entry in the Netherlands. We propose to obtain such estimates by measuring the prevalence of positive IGRA responses in immigrants at entry and by estimating the positive predictive value of the test using the known TB incidence in immigrants. The proposed study involves testing of a representative sample of 1,500 adult immigrants who qualify for chest X-ray screening at entry using both the tuberculin skin test and an IGRA. To assess the positive predictive value of the IGRA we will combine the information obtained from the IGRA testing with the information of the number of incident cases obtained from the retrospective and prospective incidence data from the notification system. The results of this study will also serve as input for a research study in which the cost-effectiveness of different interventions is assessed.