CONTINUING STUDY OF PRIMARY DRUG RESISTANCE IN TUBERCULOSIS IN VETERAN POPULATION WITHIN UNITED STATES .I.

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Abstract
This is the first report on 2 continuing surveys (the Special Research Laboratory Direct and the Special Research Laboratory Indirect Test surveys) of primary drug resistance in the US. Observations were made by direct test on 477 strains of mycobacteria isolated from an almost equivalent number of patients admitted to Veterans Administration hospitals in the northeastern portion of the US and in the Los Angeles area, between Dec, 1960, and Dec, 1962. Results suggest that the incidence of primary drug resistance at that time varied, depending on the criteria of resistance used, but did not exceed 4.7% to streptomycin, 6.1% to para-aminosalicylic acid, and 6.0% to isoniazid. Observations made by indirect test on 1,204 strains of Mycobacterium tuberculosis, likewise isolated from an almost equivalent number of untreated tuberculous patients admitted to Veterans Administration hospitals throughout the entire US, between Sept., 1962, and Sept., 1963, indicate: that small numbers (less than 20 colonies) of resistant cells within a total microbial population are not significant; and that strains requiring more than 2 gamma of streptomycin, more than 4 gamma of para-aminosalicylic acid, or more than 0.5 gamma of isoniazid/ml of medium for inhibition of growth possess some degree of resistance to these drugs. On this basis, the observed incidence of primary drug resistance among the 1,204 strains studied by the indirect test method used was low, i.e., it did not exceed a total of 3.1% to streptomycin, 2.9% to para-aminosalicylic acid, and 3.9% to isoniazid, or 1.9% to streptomycin alone, 2.1% to para-aminosalicylic acid alone, and 2.4% to isoniazid alone. Multiple drug resistance was observed infrequently, i. e., 0.3% of the strains were resistant to both isoniazid and para-aminosalicylic acid, 0.7% to both isoniazid and streptomycin, 0.08% to both streptomycin and para-aminosalicylic acid, and 0.4% to all 3 of these drugs. Techniques used in different laboratories vary, and it is difficult to compare results obtained in one with those obtained in another. One can, however, measure "change" under a constant set of conditions. The present studies encompass recent periods in time and indicate that the prevalence of primary drug resistance is now low. Of interest will be the prevalence in future years when tests are performed in an identical manner.