Analysis of rate of change of IS6110 RFLP patterns of Mycobacterium tuberculosis based on serial patient isolates

The rate of change of IS6110 restriction fragment length polymorphism (RFLP ) patterns of Mycobacterium tuberculosis was determined in serial isolates from 544 patients. In 25 patients (4.6%), the RFLP patterns of the follow-u p isolates differed from the initial isolates. Patients with different foll ow-up strains were less likely to cluster with patients whose strains had i ndistinguishable RFLP patterns. Changes in RFLP patterns were more common f or persons with extrapulmonary disease and for those who had both pulmonary and extrapulmonary isolates. Based on serial isolates spanning for the mos t part <3 months, the half-life was extrapolated to be 3.2 years (95% confi dence interval, 2.1-5.0). The main implication of this study is that the ra te of change of IS6110-based RFLP of M. tuberculosis supports the use of IS 6110 typing in epidemiologic studies of recent transmission of tuberculosis .