Evidence from molecular fingerprinting of limited spread of drug-resistanttuberculosis in Texas

To determine the contribution of recent transmission to spread of drug-resi stant tuberculosis in Texas, we performed IS6110-based and pTBN12-based res triction fragment length polymorphism (RFLP) analyses on Mycobacterium tube rculosis isolates, Isolates collected from 201 patients in Texas between 19 92 and 1994 were studied. The distribution of cases was strikingly focal. A ll cases were reported from 35 of the 254 counties in Texas, and 74% (148 o f 201) were reported from only 9 counties. One hundred sixty-one (80%) of t he patients had M. tuberculosis isolates with unique RFLP patterns, and 41 (20%) patients were in 20 clusters, each comprising 2 to 3 patients. The la rgest number of cases of drug-resistant tuberculosis were reported in count ies bordering Mexico, but the percentage of clustered cases was highest in northeast Texas and in counties that included the cities of Dallas, Fort Wo rth, and Houston. Compared to nonclustered patients, clustered patients wer e more likely to be African American and to have been born in the United St ates. Clustered patients were significantly more likely to be from the same geographic area, and clustered patients from the same geographic area were more likely to have isolates with identical drug susceptibility patterns, suggesting that they were linked by recent transmission, In 11 of 20 cluste rs, clustered patients were from geographically separate regions, and most isolates did not have identical drug susceptibility patterns, suggesting th at tuberculosis was contracted from a common source in the remote past. Bas ed on the low percentage of clustered cases and the small cluster size, we conclude that there is no evidence for the extensive transmission of drug-r esistant tuberculosis in Texas.