A nonculture test for identification of Chlamydia trachomatis

Abstract

A clinical trial compared Chlamydiazyme (Abbott Laboratories, North Chicago, Illinois), an enzyme immunoassay being developed for the detection of Chlamydia trachomatis antigens, with isolation of the organism in cycloheximide-treated McCoy cells. Duplicate cervical swab specimens were obtained from 209 women undergoing abortion. C. trachomatis was isolated after subculturing from 18 of them (8.6%). Chlamydial antigens were found with Chlamydiazyme in 13 (72.2%) of the 18. The same number was detected with primary isolation. The specificity of Chlamydiazyme was 98.4%. Overall, 201 of 209 samples (96.2%) were identified correctly with Chlamydiazyme as compared to isolation after subculturing. Therefore, Chlamydiazyme could be used instead of primary isolation in this population.

PIP: The standard isolation test for Chlamydia trachomatis involves growth of C. trachomatis in cycloheximide-treated McCoy cells, but isolation is expensive and complicated and requires special equipment, knowledge, and at least 48 hours. A recent approach to a simple, accurate, and inexpensive test without isolation involves use of enzyme immunoassays. In March 1984, the Chlamydiazyme assay from Abbott Laboratories which detects chlamydial antigens in cervical and urethral swab specimens, was tested in 209 abortion patients in Pittsburgh. 2 swab speicmens were obtained from each patient, 1 to be analyzed for C. trachomatis antigens with Chlamydiazyme and 1 to be used for chlamydial isolation tests. 80% of the patients were white and 70% were unmarried. Their ages ranged from 18-38 years with a mean age of 24.4 years. 72 had had urogenital symptoms within the preceding month. C. trachomatis was isolated in McCoy cells after subculturing from 18 of 209 patients (8.6%). C. trachomatis antigens were found with Chlamydiazyme in 13 of 18 patients (72.2%) whose specimens yielded the bacterium. The specificity of the enzyme immunoassay procedure was 98.4% (188 of 191). Overall, 201 of 209 samples (96.2%) were identified correctly with Chlamydiazyme, as compared to isolation after subculture. Of the 18 isolates, only 13 were positive on primary isolation and 5 grew on subsequent subculture. 10 of the 13 primary isolate specimens and 3 of the 5 which grew on subculture were reactive with Chlamydiazyme. The same number of infections was detected with Chlamydiazyme and primary isolation, although only 10 of 13 patients were positive with both methods. 3 specimens were reactive with Chlamydiazyme although organisms were not isolated. 2 of the 3 patients had vaginal discharge. 2 of the 3 were recultured within 6 weeks and both yielded positive Chlamydiazyme results in the absence of C. trachomatis isolation. It was considered unlikely that C. trachomatis would be isolated since all patients had received prophylactic tetracycline treatment after the abortion procedures.