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

Objective: To determine the tuberculosis (TB) transmission patterns within the prison system in Catalonia, conventional epidemiological techniques wer e combined with DNA fingerprinting of Mycobacterium tuberculosis. Methods: IS6110- and polymorphic GC-rich repeat sequence (PGRS)-based restr iction fragment length polymorphism (RFLP) were combined with epidemiologic al studies to assess the relatedness of isolates from all patients with con firmed TB at five prisons in the province of Barcelona (Catalonia, Spain), between 1 July 1994 and 31 December 1996. Risk factors for transmission wer e analysed to a logistic regression. The extent of drug-resistant TB was al so assessed. Results: 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 epid emiological methods, 14 active chains of transmission were identified in pr ison involving 65 isolates (52% of clustered patients). A lengthy history o f 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 associate d with clustering. Low rates of both initial (2.9%;) and acquired drug resi stance (5.8%) were identified and there was no evidence of the transmission of drug-resistant TB. Conclusion: In the prison system studied, the recent transmission of TB con tributes substantially to the overall incidence of the disease. Both length y 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 resista nce and for avoiding the transmission of resistant organisms. (C) 2000 Lipp incott Williams Wilkins.