PATTERNS OF DETECTION OF STRONGYLOIDES-STERCORALIS IN STOOL SPECIMENS- IMPLICATIONS FOR DIAGNOSIS AND CLINICAL-TRIALS

Reported efficacies of drugs used to treat Strongyloides stercoralis i nfection vary widely, Because diagnostic methods are insensitive, ther apeutic trials generally require multiple negative posttreatment stool specimens as evidence of drug efficacy. However, only a single positi ve stool specimen is usually required for study enrollment, To determi ne the reproducibility of detection of S. stercoralis larvae in the st ool, 108 asymptomatic infected men submitted 25 g of fresh stool once a week for eight consecutive weeks for examination by the Baermann tec hnique. During the 8-week study, 239 (27.7%) of 864 stool specimens we re positive for S. stercoralis, Rates of detection of larvae in the st ool specimens ranged from eight of eight specimens in 3 (2.8%) men to none of eight specimens in 36 (33.3%) men, Of 43 men for whom S. sterc oralis was detected in at least two of the first four stool specimens, only 1 (2.3%) man tested negative on all of the next four specimens, In comparison, of 29 men who had detectable larvae in only one of the first four specimens, 22 (75.9%) tested negative on all of the next fo ur samples, Thus, if these 29 men had been enrolled in a therapeutic t rial between the first and second sets of four specimens, the efficacy of a drug with no activity against this parasite would have been esti mated to be 76%. These data suggest that patterns of S. stercoralis de tection vary widely among infected persons and that intermittent larva l shedding can lead to inflated estimates of drug efficacy, Before a p atient is entered in a clinical trial of drug efficacy, four consecuti ve stool specimens should be examined for S. stercoralis; only persons with two or more positive specimens should be enrolled.