Recognition by TB patients of facial photographs of other TB patients, when combined with restriction fragment length polymorphism (RFLP) analysis of specimens to determine disease clustering, can enhance TB control by showing epidemiologic links between these people, according to a study in the July 1st issue of American Journal of Respiratory and Critical Care Medicine ("Transmission Dynamics of Tuberculosis in Tarrant County, Texas," 2002;166:36-42).

Stephen E. Weis, D.O., of the Division of Public Health, Department of Medicine, University of North Texas Health Science Center, along with six colleagues, studied 159 subjects, with 76 of the patients (48 percent) linked in 19 clusters. When studied with RFLP, patients who had specimens (isolates) that were identical or closely related were considered part of a cluster. A total of 17 of the 19 clusters had the photographs needed for recognition analysis. "Our findings provide the first evidence that the combination of RFLP analysis and photographic recognition of clustered patients with TB can facilitate identification of sites of tuberculosis transmission," said Weis.

Weis noted that since a total of 48 percent of the patients were clustered in 19 clusters, it suggested that recent transmission accounted for 36 percent of the TB cases in Tarrant County. "We found four homeless shelters and five bars were frequented significantly more often by patients infected with specific TB strains," Weis added.

In Tarrant County there are approximately 1,963 bars, so screening at all bars is not feasible. However, one shelter and one bar were shown to be independent predictors of clustering, suggesting that they were the sites of TB transmission.

The investigators found that patients in half the clusters recognized more photographs of people in their cluster, suggesting that there was significant contact among clustered patients. In most clusters, this contact was limited, occurring in the setting of work, labor pools, or in bars, according to the authors. Often, patients did not know the full name of the person whose photograph they recognized. The researchers said their data confirm previous reports that casual contact can result in extensive transmission of TB.

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