Rapid antigen tests for Neisseria gonorrhoeae and Chlamydia trachomatis are not accurate for screening women with disturbed vaginal lactobacillary flora.

We studied the accuracy of the rapid antigen detection tests Gonozyme and Chlamydiazyme in high-risk women in an outpatient prenatal clinic, Kalafong University Hospital, Pretoria, South Africa. Women (n = 433) presenting with uneventful pregnancy (n = 324), unavoidable miscarriage (n = 41) or infertility of 1 year's duration (n = 68) had a Pap smear for lactobacillary grading and detection of pathogens like Candida albicans or Trichomonas vaginalis, a swab for culture of Neisseria gonorrhoeae, and a swab for Gonozyme, Chlamydiazyme and Chlamydia immunofluorescence collected from the endocervix. Specificities of both antigen tests were high, but sensitivities and positive predictive values were disappointingly low. Chlamydial antigen was recovered in only 37% of samples with positive immunofluorescence, gonococcal antigen was detected in only 50% of samples with positive culture for N. gonorrhoeae. Although prevalence of N. gonorrhoeae, Chlamydia trachomatis and Trichomonas vaginalis was higher in women with disturbed lactobacillary grades on the Pap smears, sensitivities of the antigen tests were lower in this group. We conclude that detection of endocervical antigens of C. trachomatis and N. gonorrhoeae lacked sensitivity in pregnant and infertile women living in an area with high prevalence of chlamydial cervicitis, gonorrhoea and Trichomonas vaginitis. Furthermore, the rapid antigen tests lack accuracy when the lactobacillary flora is disturbed and are, therefore, not suitable for detection of C. trachomatis or N. gonorrhoeae in pre-screened patients.