Routine use of the Gen-Probe MTD2 amplification test for detection of Mycobacterium tuberculosis in clinical specimens in a large public health mycobacteriology laboratory.

The new version of the Amplified Mycobacterium Tuberculosis Direct Test, MTD2 (Gen-Probe Inc., San Diego, CA) has been implemented as part of the regular testing algorithm for detecting Mycobacterium tuberculosis (MTB) in selected respiratory and non-respiratory specimens in our laboratory. At the Central Public Health Laboratory, Etobicoke, Ontario, we receive specimens for the detection of mycobacteria from all areas of the Province of Ontario. The laboratory processes approximately 25,000 specimens per year, and receives approximately 2000 reference cultures for identification. There are 600 to 700 new cases of tuberculosis detected yearly. Over the 1-year period (1997-98), 823 specimens were tested by MTD2 and the results were compared with radiometric culture (Bactec, Becton Dickinson, Sparks, MD) and clinical diagnosis, giving an overall sensitivity, specificity, positive predictive value and negative predictive values of 100%, 99.6%, 97.4% and 100%, respectively. Two hundred and two cases of respiratory TB and 56 cases of extrapulmonary TB were detected by MTD2 within 0-4 days of specimen arrival in the laboratory. By appropriate selection of specimens for testing, the MTD2 can provide a fast, accurate, and cost-effective method for the detection of MTB in clinical specimens.