Geospatial and Molecular Clustering of Mycobacterium tuberculosis, Tarrant County, TX, 1993-2000

Molecularly clustered cases are assumed to be the result of recent transmission of those in the cluster. An intervention that targets clustered cases with recent transmission, such as identifying contacts of active cases, could be effective as a programmatic control measure. The purpose of this study is to identify areas of recent transmission, whereby determining the contribution of geospatial and molecular clustering to the local tuberculosis morbidity. Tuberculosis cases due to recent transmission have important implications for tuberculosis control programs. They suggest that current methods of case-finding, investigations of susceptible contacts, and the provision of preventive therapy are ineffective in interrupting some transmission. This study utilized molecular strain characteristics and GIS technology to uncover geographical links to on-going transmission, where tradition public health surveillance methods are failing. Risk behaviors such as illicit drug use, crack-cocaine use, jail experience, and sexual relations with a prostitute were strongly associated with on-going transmission. Place factors, specifically where patients reside, was also found to be significantly associated for certain zip codes in Tarrant County. Cases in urban zip codes 76102 [OR=3.954; 95% CI=1.803, 8.671] and 76105 [OR=3.135; CI=1.254, 7.835] were strongly associated to infection with a clustered strain when compared to the rest of the county. The use of Geographical Informational Systems (GIS) technology and molecular strain typing provides a proactive approach that may be used to initiate traditional surveillance investigations. As an application utility, this project will be used to develop more effective means of tuberculosis control within Tarrant County.