An Evaluation Of Intraderaml Tests For The Screening Of Paragonimiasis By Comparing Antigens Variously Processed.
An evaluation of intradermal test in screening paragonimiasis was attempted by comparing antigens, filtered through Sephadex G 50, fractionated by DEAE Sephadex A 25, and V.B.S.(crude extract of adult worms) antigen on 402 school children. The sensitivity and false negative rates were compared with one another on results of two examinations for eggs, one with sputum and the other with stool. The purified antigens showed more intense skin reaction than the crude extract. The crude extrct(V.B.S.) appeared to have lower false negative rate than the purified even though the difference was not statistically significant. Intradermal test with V.B.S. antigen on 12,000 subjects was analysed to find some characteristics of the reaction. Three size groups were classified by egg detection rate; negative reaction, 20~50 mm(2) size group of which egg detection rate was 3.5% among 118 persons, intermediate, 60~100 mm(2) with 26.8% among 1,078, and positive reaction, larger than 100 mm(2) with 45.7% among 2,098 subjects. The distribution of wheal size by age for total population surveyed revealed that younger ages had smaller wheal sizes with larger proportion of negative reaction, which decreased when the age increased. Skin sensitization in a population seemed to occur gradually to and reached a maximum by the age of 13 year. The egg detection rate increased proportionately to wheal size for the intermediate group, however, it did not vary much by size for positive group(larger than 100 mm(2)). When the wheal size distributions were compared in three groups, egg positives, egg negatives, and the group whose sputa were not examined, curves of the two groups, egg positive and negative, did not show clear separation. This fact seems to indicate that there is a low sensitivity and specificity in both tests(sputum and skin). The stability of the intradermal test measured by a second survey done one year after the primary survey revealed that the intermediate size group had more marked unstability than the other groups, and the treated group had tendency to decrease in wheal size. The purification of antigen for intradermal test did not add any better means of screening for paragonimiasis, probably due to the nature of skin sensitization evoked by many elements of the parasite but not by a few selected components. The V.B.S. antigen may be valuable for screening a large population, yet the diagnosis can not be dependent entirely upon the test. The final diagnosis should be made by repeated sputum examinations in spaced time with careful history taking aided by CF test and X-ray examination if necessary.
Kim
Joung Soon
JS
Department of Epidemiology, School of Public Health, Seoul National University, Seoul, Korea.