Predictors of tuberculosis transmission in prisons: an analysis using conventional and molecular methods

To determine the tuberculosis (TB) transmission patterns within the prison system in Catalonia, conventional epidemiological techniques were combined with DNA fingerprinting of Mycobacterium tuberculosis.

IS6110- and polymorphic GC-rich repeat sequence (PGRS)-based restriction fragment length polymorphism (RFLP) were combined with epidemiological studies to assess the relatedness of isolates from all patients with confirmed TB at five prisons in the province of Barcelona (Catalonia, Spain), between 1 July 1994 and 31 December 1996. Risk factors for transmission were analysed to a logistic regression. The extent of drug-resistant TB was also assessed.

The incidence of TB during the study period was 2775 cases per 100,000 inmate years. Of the 247 culture-positive cases, 126 (51%) appeared to have active TB as a result of recent transmission. Using conventional epidemiological methods, 14 active chains of transmission were identified in prison involving 65 isolates (52% of clustered patients). A lengthy history of imprisonment [odds ratio (OR) 2.8, 95% confidence interval (CI) 1.52-5.11] and pulmonary TB (OR 2.36, 95% CI 1.17-4.75) were independently associated with clustering. Low rates of both initial (2.9%) and acquired drug resistance (5.8%) were identified and there was no evidence of the transmission of drug-resistant TB.

In the prison system studied, the recent transmission of TB contributes substantially to the overall incidence of the disease. Both lengthy incarcerations and delays in identifying inmates with pulmonary symptoms play a key role in this recent transmission. Directly observed therapy (DOT) is a critical control strategy for reducing the emergence of drug resistance and for avoiding the transmission of resistant organisms.