Transmission patterns of tuberculosis in Taiwan: Analysis by restriction fragment length polymorphism

Abstract

Objectives: To study the pattern of tuberculosis transmission in Taiwan. Methods: An insertion sequence IS 6110-based restriction fragment length polymorphism (RFLP) analysis of Mycobacterium tuberculosis isolates was conducted. Results: Among 85 patients with culture-confirmed tuberculosis diagnosed between August 1993 and March 1994, 79 (93%) had isolates with unique RFLP patterns, whereas 6 (7%) had isolates that belonged to three clusters of identical RFLP patterns. Two strains in one cluster were isolated from patients who lived in the same small village. The average age of the patients was 54 years, and more than 40% had an underlying medical problem. The high degree of diversity of the RFLP patterns, and the demographic and clinical characteristics of the patients suggest that, in Taiwan, a large proportion of newly diagnosed tuberculosis cases are attributable to reactivation of an infection acquired in the remote past. These observations contrast with those in communities with a high prevalence of human immunodeficiency virus (HIV) infections, where a large proportion of new tuberculosis cases may be attributable to recent infections. Conclusions: The findings suggest that the distribution of M. tuberculosis with identical RFLP patterns (representing recent transmissions) may be greatly influenced by the prevalence of HIV infections in the community. In addition, the steady decline in the incidence of tuberculosis in Taiwan, despite its relatively high incidence, suggests that the trend in disease incidence may be influenced by the prevalence of cluster strains in the community.