A continuing survey of primary drug resistance in tuberculosis, 1961 to 1968. A U.S. Public Health Service cooperative study.

From 1961 through 1968 the incidence of primary drug resistance was monitored among patients admitted to 22 participating hospitals. The patients were believed to have newly diagnosed, previously untreated, bacteriologically proved pulmonary tuberculosis. During the study period the level of primary resistance to isoniazid, streptomycin, and para-aminosalicylic acid remained very low; there was no indication that primary resistance to these drugs was increasing. Investigation of patient histories revealed that a significant proportion of persons initially believed to have been previously untreated actually had received prior chemotherapy. Resistance rates to both isoniazid and streptomycin were significantly higher among younger patients than among older patients. No relationship was found between race or sex and primary resistance rates. The low incidence of drug resistance found in this survey suggests that disease caused by virulent resistant organisms occurs infrequently.