Significance of Scotch-tape anal swab technique in diagnosis of Enterobius vermicularis infection

Abstract

The significance of Scotch-tape anal swab technique was evaluated in three communities of Korea, one in orphanage institute and two in rural populations, from November to December, 1975. Based on the epidemiological concept that the prevalence rate of Enterobius vermicularis infection in a community as "the proportion in the population who harboured E. vermicularis at certain point of time", the present authors treated the whole surveyed population with pyrantel pamoate disregard to the results of Scotch-tape anal swab and collected pinworms expelled in stool specimens during 2 consecutive days after the chemotherapy. Although the present authors could not collect the younger adult worms less than 3.54 mm in length after chemotherapy, the positive rates of pinworm collection in three surveyed communities were 80.6%, 92.5% and 91.4% respectively whereas the positive rates of single Scotch-tape anal swab were 52.4%, 53.6% and 57.1% respectively. These results denote that results of single anal swab do not represent the prevalence rate of Enterobius infection in a community. The results of successive two anal swabs and estimation of positivity in a population using Neyman's "Best asymptotically normal estimate" revealed 62.9% in the third trial group of this study and probability of finding eggs in single slide was 0.869. Comparing with the pinworm collection rate after the chemotherapy in this group the estimated positive rate was by far lower than that of pinworm collection(89.3%). The positive results of single anal swab did not correspond to the pinworm collection in average 9.1% of anal swab positive cases and the negative results did not correspond to pinworm collection in 81.3% of anal swab negative cases, when the data from three surveyed communities were amalgamated. These results must come from the principle of anal swab that detect the terminated parasitism. With rare exceptions, the anal swab negative cases harbour relatively fewer number of Enterobius than those of positive cases. And the mean number of E. vermicularis collected from anal swab negative cases was 9.1 whereas the number in anal swab positive cases was 31.5. By analyzing the data on the relationship between bathing interval and anal swab positive conversion, it was assumed that the positive rate of anal swab in a community represent the rate of appearance of gravid female Enterobius vermicularis through anus during approximately past two days prior to examination.