In HIV-infected patients from a low prevalence TB country, both interferon-gamma assays are more sensitive than TST, but seem to be less sensitive than in immunocompetent patients. The blood tests show poor agreement and differ in their dependence on the CD4 cell count.

A novel targeted TB screening approach with voluntary radiographic examination of illicit drug users and homeless persons can be integrated into the existing public TB prevention programme and provides a high case-finding rate.

PurposeFew individuals that are latently infected with M. tuberculosis latent tuberculosis infection(LTBI) progress to active disease. We investigated risk factors for LTBI and active pulmonary tuberculosis (PTB) in Germany.MethodsHealthy household contacts (HHCs), health care workers (HCWs) exposed to M. tuberculosis and PTB patients were recruited at 18 German centres. Interferon-γ release assay (IGRA) testing was performed. LTBI risk factors were evaluated by comparing IGRA-positive with IGRA-negative contacts. Risk factors for tuberculosis were evaluated by comparing PTB patients with HHCs.ResultsFrom 2008–2014, 603 HHCs, 295 HCWs and 856 PTBs were recruited. LTBI was found in 34.5% of HHCs and in 38.9% of HCWs. In HCWs, care for coughing patients (p = 0.02) and longstanding nursing occupation (p = 0.04) were associated with LTBI. In HHCs, predictors for LTBI were a diseased partner (odds ratio 4.39), sexual contact to a diseased partner and substance dependency (all p < 0.001). PTB was associated with male sex, low body weight (p < 0.0001), alcoholism (15.0 vs 5.9%; p < 0.0001), glucocorticoid therapy (7.2 vs 2.0%; p = 0.004) and diabetes (7.8 vs. 4.0%; p = 0.04). No contact developed active tuberculosis within 2 years follow-up.ConclusionsPositive IGRA responses are frequent among exposed HHCs and HCWs in Germany and are poor predictors for the development of active tuberculosis.Electronic supplementary materialThe online version of this article (doi:10.1007/s15010-016-0963-2) contains supplementary material, which is available to authorized users.

Strategies for control and elimination of tuberculosis (TB) in low-incidence settings are directed toward treatment of recently acquired latent tuberculosis infection (LTBI) in TB contacts [1]. To identify this target population for preventive treatment the development of more specific, in vitro assays for LTBI, the interferon (INF)-c release assays (IGRAs), has offered an alternative method for LTBI diagnosis. Although IGRAs are increasingly recommended in national guidelines, evidence that positive IGRA results are prognostic for developing TB is still limited [2,3], especially outside of prospective studies with welldefined inclusion criteria. Therefore, we investigated progression towards active TB among IGRA positive contacts of active TB cases under routine field conditions and calculated the positive predictive value (PPV) for progression and the number needed to treat (NNT) with preventive treatment to prevent one incident TB case. Additionally, we introduced different cut-off values for IGRA positivity and compared the computed progression rates. Among all contacts with a positive tuberculosis-specific IGRA we describe the uptake of preventive treatment.Our study covered a population of 3.2 million with a reported TB incidence of 7.5 cases per 100 000 population in 2008. From 2008 to 2010, we prospectively recruited all IGRA-positive contacts of newly detected sputum smear and/or culture positive notified TB cases at 12 local public health authorities (LPHAs) in Hesse, Germany. Only contacts with a history of TB disease were excluded.

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