Screening of health care workers by means of Quantiferon® test for detecting M. tuberculosis infection

Tuberculosis (Tbc) may still represent a real problem in the Western World, due to the recent epidemics of Human Immunodeficiency Virus (HIV) and to the increasing immigration rate of people originating from countries in which the disease is endemic. For this reason, the risk of contracting and/or transmitting the mycobacterium (even in the absence of overt disease), may be of concern for selected populations, in particular health care workers. According to the current Italian legislation, the test to be used for detecting latent tuberculosis is the Mantoux test, which however, suffers several methodological weaknesses, such as the high rate of false positive results in vaccinated population, the subjectivity of the evaluation, and the possibility of false positive results with serial determinations ("booster effect"). Recently introduced "in vitro" serological tests, may overcome these problems. In this study we therefore evaluated the prevalence of positive tests in a population of young health care workers (many of whom vaccinated against Tbc), by applying the Quantiferon® test, which is based on the production of interferon gamma by the analyzed blood, when checked with specific tubercular antigens. The examination was performed on 298 health care workers (24 of whom at a relatively high risk for a contact with a tubercular patient). The prevalence of positive tests was 2 out of 274 (0.7%) in the medium risk group, and 2 out of 24 (8.3%) in the high risk group. The overall prevalence (4 out of 298, 1.7%) was however much lower than the rate of about 12% estimated on Mantoux-based findings. Our data confirm therefore the strong reduction of false positive findings by applying the Quantiferon® test in health care workers, and make the application of this test attractive even in economic terms, in spite of the relatively high cost of single test determinations.