Resistance to antituberculosis drugs in rural South Africa: rates, patterns, risks, and transmission dynamics

This study describes the rate, pattern, and transmission dynamics of, and risk factors for, isolates of Mycobacterium tuberculosis resistant to antituberculosis drugs in a rural South African health district. Twenty-one of 254 (7.6%; 95% confidence interval [CI] 4.8-11.4) isolates from incident cases were resistant to at least one drug (isoniazid, rifampicin, streptomycin, ethambutol). A random sample of 28 otherwise susceptible isolates and all 21 resistant isolates were susceptible to pyrazinamide. There was one case of combined isoniazid/rifampicin resistance. The rate of initial resistance was 8.1% (95% CI 4.9-12.4) and of acquired resistance 6.2% (95% CI 1.9-14.2). Age, sex, known human immunodeficiency virus status, and previous treatment history were not associated with drug resistance. Restriction fragment length polymorphism (RFLP) analysis of 13 of the 21 resistant specimens showed 12 different banding patterns. Rates of drug resistance were low in this representative sample of patients from a defined geographical area. Previous treatment history was probably not a risk factor because of the use of multiple drug regimens, directly observed therapy, and high completion rates in those previously treated. Although limited in number, the RFLP data suggested that recent local transmission of resistant strains was not occurring to a significant extent.