Primary Drug Resistance1,2

Abstract

Observations were made by direct test on 170 strains of mycobacteria from patients with newly diagnosed and previously untreated tuberculosis, or pulmonary disease simulating tuberculosis, admitted to Veterans Administration hospitals in the northeastern portion of the United States and in the Los Angeles area between December 1962 and December 1963. The incidence of primary drug resistance during that period did not exceed 1.9% to streptomycin, 1.9% to isoniazid, and 2.2% to para-aminosalicylic acid. Only 0.8% of all strains of M. tuberculosis tested against streptomycin, isoniazid, and PAS, were resistant to 2 of these drugs. None were resistant to all 3 drugs. The inclusion of 2 strains of mycobacteria other than tubercle bacilli increased the observed incidence of primary drug resistance to PAS to 2.9%, and of multiple drug resistance to 2.3%. When these data are compared with those obtained by the same procedures on patients admitted to the same hospitals between 1960 and 1962, it is apparent that no significant increase in primary drug resistance occurred.