[Study on the cause of tuberculosis recurrence by Mycobacterium tuberculosis genotyping method].

OBJECTIVE: To study the contribution of exogenous reinfection to tuberculosis recurrence. METHODS: Mycobacterium tuberculosis isolates from patients who had experienced 2 successive tuberculosis episodes during the years from January 1999 to March 2004 were genotyped by mycobacterial interspersed repetitive units (MIRU) method. The cause of tuberculosis recurrence was determined by comparing the MIRU pattern of Mycobacterium tuberculosis isolates responsible for different tuberculosis episodes from patients. RESULTS: Of 37 qualified patients with recurrent tuberculosis, the isolates from 25 patients in their two tuberculosis episodes showed different MIRU patterns, indicating that 68% recurrent patients were due to exogenous reinfection. The exogenous reinfection rate decreased with the age from 3/3 (under 30 years) to 73% (11/15, 30 to 60 years) and 58% (11/19, over 60 years). The frequency of exogenous reinfection increased with the tuberculosis recurrent interval. Within 6 months, the exogenous reinfection accounted for 58% (7/12) of all the recurrence, while for the time more than one year, the percentage increased to 79% (11/14). CONCLUSIONS: Exogenous reinfection was a major cause of tuberculosis recurrence in Shanghai. MIRU genotyping method is useful to study the cause of tuberculosis recurrence.