THE FLUORESCENT ANTITOXIN TEST FOR THE IMMEDIATE DIAGNOSIS OF DIPHTHERIA

Abstract

The recent increase in the incidence of diphtheria in our area stimulated the search for a reliable laboratory test for the immediate differential diagnosis of diphtheritic and non-diphtheritic membranous tonsillitis. Fluorescein-conjugated diphtheria antitoxin proved to be highly specific for staining toxigenic C. diphtheriae. Eight of nine patients with proved diphtheria had fluorescent organisms on a smear of exudate. The failure in the one case is attributed to the poor quality of the specimen obtained. An early case of diphtheria was detected by examination of family contacts of one of the patients in this series. The conjugated antitoxin does not result in fluorescent staining of nontoxigenic diphtheria bacilli on of other bacteria commonly found in the nasopharyngeal tract. Fluorescent staining of cultures suggests that only a small proportion of the potentially toxigenic diphtheria organisms are actually producing toxin at a given moment. The fluorescent antitoxin test can be performed within 1 hour. A positive result of the test is an absolute indication for antitoxin therapy. With a negative result the physician must still rely on his clinical judgment and cultural and virulence tests.