Comparison of microscopy, culture and enzyme immunoassay (Gonozyme) for the detection of Neisseria gonorrhoeae in urogenital specimens.

Urogenital specimens of male patients and female prostitutes were examined for gonorrhoea in a gonococcal antigen enzyme immunoassay (Gonozyme), by microscopic examination of stained smears and by bacterial culture. Out of 18 male patients, 14 showed positive reactions (all 14 by Gonozyme and by microscopy, but only eight by culture also). The sensitivity and specificity of Gonozyme was 100% in reference to microscopy. The predictive value for a positive test and for a negative test was 100%. The sensitivity of Gonozyme in reference to culture was also 100%, but the specificity was only 40%, because of the low yield of positive cultures. The predictive value for a positive test was 57% and for a negative test 100%. Out of 189 female prostitutes, 41 (22%) had a positive reaction in at least one test (Gonozyme, microscopy and culture were positive in 10; Gonozyme and culture in three; Gonozyme and microscopy in 14; Gonozyme alone in 11; culture alone in three). The sensitivity of Gonozyme was 100% and specificity 92% in reference to microscopy. The predictive value for a positive test was 63% and for a negative test 100%. In reference to culture, the sensitivity was 81% and specificity 86%. The predictive value for a positive test was 34% and for a negative test 98%. In prostitutes, the rate of asymptomatic infections was 14%, if one assumed that all Gonozyme-positive results were truly positive. Gonozyme proved to be the most sensitive method for screening female patients. To discriminate possibly false positive reactions, Gonozyme-positive specimens should be corroborated, preferably by bacterial cultivation.