Tuberculosis (TB) continues to be a major cause of disability and death and it has become a real problem in industrialized countries. The spread of HIV, the increasing immigration rate of people from countries with endemic TB and the growth of drug-resistant Mycobacterium tuberculosis strains extend its impact. Since the spread of the infection occurs early, health care workers are particularly exposed to the risk of contracting and/or transmitting the mycobacterium. In health care settings, policies and procedures for TB control should be developed, including health surveillance. Until recently the tuberculin skin test was the only available method for diagnosing tuberculosis, however it suffers several methodological weaknesses: high rate of false positive results in vaccinated populations, the subjectivity of the evaluation and the booster effect. Recently, the introduction of new in vitro serological tests, as the Quantiferon TB-Gold in tube (QFT-TB), may overcome these problems. The QFT-TB is based on the quantification of interferon-gamma released from sensitized lymphocytes in whole blood incubated overnight with PPD from M. tuberculosis and control antigens. The present study was performed on 27 nuns (homeless shelter staff) who were at risk for contracting tuberculosis. The prevalence of positive tests was 15 out 27 (55.5%).