Two tuberculosis genotyping clusters, one preventable outbreak.

In 2006, eight community tuberculosis (TB) cases and a ninth incarceration-related case were identified during an outbreak investigation, which included genotyping of all Mycobacterium tuberculosis isolates. In 1996, the source patient had pulmonary TB but completed only two weeks of treatment. From February 2005 to May 2006, the source patient lived in four different locations while contagious. The outbreak cases had matching isolate spoligotypes; however, the mycobacterial interspersed repetitive unit (MIRU) patterns from isolates from two secondary cases differed by one tandem repeat at a single MIRU locus. The source patient's isolates showed a mixed mycobacterial population with both MIRU patterns. Traditional and molecular epidemiologic methods linked eight secondary TB cases to a single source patient whose incomplete initial treatment, incarceration, delayed diagnosis, and housing instability resulted in extensive transmission. Adequate treatment of the source patient's initial TB or early diagnosis of recurrent TB could have prevented this outbreak.