Diphtheria carriers and the effect of erythromycin therapy

One hundred and fourteen Corynebacterium diphtheriae, toxigenic, gravis type, pharyngeal carriers were identified during a diphtheria epidemic in Elgin, Texas. All carriers were treated with erythromycin estolate, 1 g/day in divided doses for 6 days. Serial pharyngeal cultures were obtained in order to monitor the bacteriological response. Seventy-two carriers had positive cultures immediately prior to the start of therapy, and only these individuals were considered in the analysis of the effects of erythromycin. Forty-eight hours after institution of therapy, 96% of the carriers had become culture negative; all were negative by the 4th day of therapy, and all remained culture negative while taking the drug. Two days after cessation of therapy, all but one (99%) were culture negative. However, upon reculture 2 weeks later, 15 (21%) had relapsed to the carrier state. There were no significant differences in the serum diphtheria antitoxin levels, immunization status, age, sex, or socioeconomic status of those who relapsed and those who remained culture negative. This study demonstrates that erythromycin is effective in converting carriers to culture-negative status, but when given for only 6 days it is associated with large numbers of relapses. Because previous studies have not included follow-up cultures 2 weeks after therapy, it is suggested that all C. diphtheriae carriers be treated with either erythromycin or penicillin and that all be recultured at a minimum of 2 weeks after completion of therapy to assure eradication of the diphtheria organisms.