Specificity of a whole blood IGRA in German nursing students
- Equal contributors
1 University Medical Center Hamburg-Eppendorf, Institute for Health Service Research in Dermatology and Nursing - Hamburg, Martini Str. 42, 20246 Hamburg, Germany
2 Hannover Medical School, Department of Respiratory Medicine, 30625 Hannover, Germany
3 Vivantes Institute for Corporate Health und Safety, Oranienburgerstr. 285, 13437 Berlin, Germany
4 Vivantes Medical Centre Neukölln, Internal Medicine and Pneumology, Rudower Straße 48, 12351 Berlin, Germany
BMC Infectious Diseases 2011, 11:245 doi:10.1186/1471-2334-11-245Published: 19 September 2011
Interferon-gamma release assays (IGRA) are used for tuberculosis (TB) screening in healthcare workers (HCWs). However, data on specificity of IGRA in serial testing of HCWs is sparse. Therefore the specificity and the negative predictive value of the IGRA - QuantiFERON-TB Gold In-Tube (QFT) - in German nursing students was investigated.
194 nursing students at the start of their professional career were tested with the QFT. 14 nursing students were excluded from the specificity analysis, due to exposure to mycobacterium tuberculosis. Two of these subjects were QFT- positive. None of them developed disease during the year of follow-up. A study group of 180 students, all with very low risk of prior TB infection, remained in the specificity analysis. Subjects were monitored for at least two years with respect to the development of active TB disease. IGRA was performed at the start of the training and after one year.
The mean age of the study group (n = 180) was 23 years (range 18-53) with 70.9% female and 99.4% German born. The specificity of QFT was 98.9% (178/180; 95% CI 0.96-0.99); lowering the cut-off from 0.35 IU/ml to 0.1 IU/ml would have decreased specificity only slightly to 97.8% (176/180; 95% CI 0.94-0.99). Of the 154 nursing students available for re-testing, one student who initially scored positive reverted to negative, and one student initially negative converted to positive. None of the monitored group with initially negative QFT results developed TB disease, indicating a high negative predictive value of the IGRA in this population.
Following our data, QFT can serve as an effective tool in pre-employment TB screenings for HCWs. As its negative results were stable over time, specificity of the QFT in serial testing of HCWs is high. As the risk of acquiring TB infection in the German healthcare system appears to be low, our data supports the recommendation of performing TB screening only in those HCWs with known contact to TB patients or infectious materials.