Skin test reactions to Mycobacterium tuberculosis purified protein derivative and Mycobacterium avium sensitin among health care workers and medical students in the United States

SETTING: Health care workers and medical students in the United States subject to annual tuberculin skin testing. OBJECTIVE: To use skin testing with Mycobacterium avium sensitin (MAS) to determine contemporary rates of infection with non-tuberculous mycobacteria (NTM) and their effect on reactions to M. tuberculosis purified protein derivative (PPD). DESIGN: Dual skin testing was performed with PPD and MAS on 784 health care workers and medical students in the northern and southern US. MAS reactions that were greater than or equal to5 mm and also greater than or equal to3 mm larger than the PPD reaction were defined as MAS dominant and due to NTM. RESULTS: AAAS reactions were greater than or equal to5 mm. in 40% and greater than or equal to 15 mm in 18% of subjects; 95% were MAS dominant. MAS dominant reactions were more common in the south than the north (P < 0.001). PPD reactions were greater than or equal to 15 mm in 3% of subjects. PPD reactions greater than or equal to 15 ram were more common among males, foreign born subjects and subjects with BCG immunization (all P < 0.001). MAS dominant reactions were found in 82% of subjects with 5-9 mm PPD reactions and 50% with 10-14 mm PPD reactions; these reactions were more common among whites (P = 0.046), US-born (P = 0.038) and subjects without BCG immunization (P = 0.004). CONCLUSIONS: Infections with NTM are responsible for the majority of 5-14 mm PPD reactions among US-born health care workers and medical students subject to annual tuberculin testing.