Patient and cluster characteristics of tuberculosis (TB) genotype clusters and associated risk of the cluster becoming an outbreak within 24 months after diagnosis of the 3rd patient.

*One or more of 1st three patients had characteristic.1Patient had acid fast bacilli smear-positive sputum specimens and abnormal chest radiograph results with evidence of cavities.2Patient had isoniazid (INH) and rifampicin (RIF) drug resistance reported in initial susceptibility drug test.3Median values for socioeconomic measures were derived from the 2000 U.S. Census for all zip codes. A cluster was considered “exposed” if the zip code with the most cases had a value above the median.