Transmission dynamics and molecular characterization of Mycobacterium tuberculosis isolates with low copy numbers of IS6110

Population-based analysis of Mycobacterium tuberculosis transmission in Hou ston, Tex,, over 5 years identified 377 patients infected with an isolate c ontaining one to four copies of IS6110, The isolates were analyzed by spoli gotyping and assigned to one of three major genetic groups based on nucleot ide polymorphisms in codons katG 463 and gyrA 95, Prospectively obtained pa tient interviews were reviewed to assess epidemiologic links between appare ntly clustered patients. A total of 13 groups of isolates with the same IS6 110 profile were identified, representing 326 of the 377 patients (86.5%; r ange 2 to 113 patients). In contrast, 28 groups of isolates containing 334 patients (88.6%) had the same spoligotype (range, 2 to 143 patients). Combi nation of IS6110 profile and spoligotype data identified 31 clusters with 3 00 patients (79.6%; range, 2 to 82 patients). All 377 Isolates belonged to major genetic group 1 (77 patients) or genetic group 2 (300 patients); no m ajor genetic group 3 isolates were identified. Among the 228 patients inter viewed, 33 patients (14.5%) were directly linked to another patient in the same cluster. Possible epidemiologic links were also found among 11 patient s. Moreover, many clusters consisted of individuals with the same ethnicity . In conclusion, we confirmed that IS6110 profiling and spoligotyping toget her provide enhanced molecular discrimination of M. tuberculosis isolates w ith low copy numbers of IS6110. Identification of epidemiologic links among some of the patients verified that the combination of these two methods re liably indexes tuberculosis transmission.