Abstract

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.

PIP:

Drug resistance in patients with tuberculosis (TB) is a cause of treatment failure and relapse, and contributes to the development of multiple-drug resistance. Consecutive incident adult patients diagnosed with sputum smear-positive TB during 1994 in Hlabisa Hospital, northern KwaZulu/Natal, were studied to describe the rate, pattern, and transmission dynamics of, and risk factors for, isolates of Mycobacterium tuberculosis resistant to antituberculosis drugs. Cases currently being treated and followed were excluded from study. There were 354 incident cases of sputum smear-positive pulmonary TB registered at the hospital in 1994, although sputum specimens for culture were obtained from only 335 patients. 21 isolates from incident cases were at least partially resistant to at least either isoniazid, rifampicin, streptomycin, or 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 rates of initial and acquired resistance were 8.1% and 6.2%, respectively. Age, sex, known HIV status, and previous treatment history were not associated with drug resistance. Restriction fragment length polymorphism (RFLP) analysis of 13 of the 21 resistant specimens identified 12 different banding patterns, suggesting the absence of any significant recent local transmission of resistant strains.