Restriction fragment length polymorphism patterns of Mycobacterium tuberculosis isolates from 11 patients residing in two geographically contiguous counties, Arkansas, 1992–1998. IS6110 patterns are shown on the left and polymorphic GC-rich sequence on the right. Lane M shows M. tuberculosis strain H37Rv DNA marker (left) and 1-kb DNA ladder (right). Lane 1, isolate from patient 11; Lane 2, patient 13; Lanes 3–6, patients 4, 1, 3, and 2; Lanes 7–9, patients 10, 9, and 8; Lane 10, patient whose isolate differed by three bands and was not included in the study; and Lane 11, patient 5.