Evaluation of Gonozyme, an enzyme immunoassay for the rapid diagnosis of gonorrhea

Abstract

A new indirect enzyme immunoassay (EIA), Gonozyme (Abbott Laboratories), was assessed for rapid detection of gonococcal antigens. A correlation of optic density (OD) readings by EIA with colony counts of serial dilutions of Neisseria gonorrhoeae ATCC 19424 disclosed that EIA detected 103 CFU/ml at OD readings of 0.1 to 0.3, that EIA consistently detected ≥104 CFU/ml at OD readings of 0.6 to 1.3, and that concentrations of ≥105 CFU/ml were associated with OD readings of ≥2.0. The clinical usefulness of Gonozyme was evaluated by comparing results of EIA with those of Gram stain (GS) and culture for N. gonorrhoeae from urethral and endocervical swabs obtained prospectively in 886 randomly selected patients attending a clinic for sexually transmitted diseases. The patients evaluated included 83 female contacts of men with gonorrhea and 56 patients seen at the clinic for test of cure. In tests with 295 males, the sensitivities of GS and EIA were 91.3 and 97.1%, respectively, and both tests had specificities of >96%. In tests with 591 females, the sensitivities of GS and EIA were 51.4 and 96.4%, respectively (P < 0.0001, Z proportionality test), and the specificities were 98.7 and 86.5%, respectively (P < 0.0001). In tests with 61 females and 3 males, EIA was positive, whereas GS and cultures were negative for N. gonorrhoeae. Gonozyme is a highly sensitive method for rapid detection of gonococcal antigens. EIA is comparable to GS for males and more sensitive though less specific than GS for females. Possible reasons for the lower specificity of EIA for females are discussed. Due to its high negative predictive value for female contacts, EIA offers an alternative to epidemiological treatment of contacts before culture results.