Chlamydiazyme Assay Research Articles

The Use of a Confirmatory assay to Increase the Sensitivity and Specificity of the Chlamydiazyme Test

The blocking assay was used to reexamine 15,662 patient specimens (2,565 male specimens, 13,097 female specimens) that were submitted for Chlamydia detection using the Chlamydiazyme EIA assay (Abbott Laboratories, North Chicago, IL). Specimens that gave optical density (OD) readings between 1.99 to cutoff and between cutoff to 3 times the negative control in the Chlamydiazyme EIA assay were analyzed further by the blocking assay during the phase 1 study. In the phase 2 study, another 1,120 specimens (473 male specimens and 647 female specimens) that had the above mentioned OD range in the Chlamydiazyme assay were tested with the blocking assay and the direct fluorescent antibody test using the cytospin method. Significant finding from phase 1 study demonstrated that 42.3% of the male specimens with optical density between cutoff to three times the negative control can be blocked by blocking assay (confirmed positive), whereas only 50% of the female specimens with OD range between cutoff to .5 were blocked by the blocking assay. In the phase 2 study, similar results were obtained with the blocking assay. The direct fluorescent antibody test showed excellent correlation with the blocking assay. These data showed that both blocking or direct fluorescent antibody tests can be used for confirmation purposes to increase the sensitivity and specificity of the assay. However, for specimens with OD values below the cutoff to 3 times the negative control, it was necessary to reassess the specimens by either of the methods. This was true especially with the male specimens.

Confirmatory Testing Demonstrates That False-Positive Rates in the Chlamydiazyme Assay are Influenced by Gender and Genital Specimen Type

Confirmatory Testing Demonstrates That False-Positive Rates in the Chlamydiazyme Assay are Influenced by Gender and Genital Specimen Type

Mandatory use of confirmation stage with Chlamydiazyme during urinary sediment analysis.

To assess whether false positive results found when the first stage Chlamydiazyme test is performed on urinary sediment could be reduced by using the more specific second stage blocking assay. Sediment from 173 urine samples from patients with suspected urinary tract infection caused by Gram negative bacteria and 23 control urine samples were tested using the Chlamydiazyme assay system, which included a blocking assay. A reaction result with the first stage Chlamydiazyme assay test was seen in 102 (58.9%) of the test urine samples. First stage reactivity was not blocked by the Chlamydiazyme confirmatory assay performed on repeat testing. All were correctly identified as true negative (first test false positive) results. Use of a second (specific) blocking assay for the analysis of urinary sediment using Chlamydiazyme eliminates false positive results in Gram negative urinary tract infections.

Evaluation of chlamydiazyme enzyme immunoassay for detection of Chlamydia trachomatis in urine specimens from men

Paired first-voided urine and urethral swab specimens were collected from 540 men attending sexually transmitted disease clinics in three geographic locations. Urine specimens were tested for the presence of Chlamydia trachomatis by commercial enzyme immunoassay (Chlamydiazyme), and the results were compared with those of urethral swab cultures. Overall prevalence of urethral C. trachomatis by culture was 14%, and the Chlamydiazyme assay had an overall sensitivity of 83%, a specificity of 96%, a positive predictive value of 76%, and a negative predictive value of 97%. Sensitivity was greater (94%) in those culture-positive samples with a high antigen load (> or = 20 inclusion-forming units per coverslip) than those with a lower antigen load (68%). Assay of urine specimens from men attending sexually transmitted disease clinics by Chlamydiazyme appears to be a reliable, noninvasive method of detection of C. trachomatis infection, and further evaluation of its performance in asymptomatic and low-prevalence populations is indicated.

Confirmation of positive results for chlamydial antigen by the Chlamydiazyme assay: value of repeated testing and a blocking antibody assay.

We studied the specificity of the Abbott Chlamydiazyme test for detection of Chlamydia trachomatis antigen by means of a specific blocking antibody test. A total of 457 previously positive specimens were tested; 22 did not block in the blocking antibody test, 39 did not repeat as positive, and 396 were confirmed as positive. The distribution of A492 values obtained with specimens which did not repeat as positive was nonrandom and was concentrated between the cutoff values and 0.400. The positive predictive value of the Chlamydiazyme assay after initial testing was 86.7% (396 of 457), but the positive predictive value increased to 94.7% (396 of 418) if specimens which were not repeatedly positive were considered negative. We recommend routinely repeating the Chlamydiazyme assay for all specimens which give A492 values between the cutoff and 0.400 to eliminate many false-positive results. Use of the blocking antibody reagent can then be reserved for confirming only specimens which are repeatedly positive.

Cross-reaction of clinical isolates of bacteria and yeasts with the chlamydiazyme test for chlamydial antigen, before and after use of a blocking reagent.

More than 1,000 clinical isolates of bacteria and yeasts were identified, subcultured, and tested at 10(8) colony-forming units per milliliter with the Chlamydiazyme assay to determine the variety of microorganisms which could cause false-positive results for Chlamydial antigen. False-positive Chlamydiazyme results were obtained from 27 of 465 (5.8%) gram-negative, aerobic, or facultatively anaerobic bacterial isolates (including 8 of 39 [20.5%] Neisseria gonorrhoeae and 8 of 149 [5.4%] Escherichia coli isolates) and also from 2 of 46 (4.3%) Bacteroides species isolates. No false-positive results were obtained either from 373 gram-positive bacterial isolates or from 153 yeasts. Results from 21 of 29 (72.4%) isolates that cross-reacted with Chlamydiazyme antibodies were repeatedly positive, but all 21 were confirmed as false-positive results using a blocking antibody. When an initial Chlamydiazyme result is positive, repeating the test, with and without use of the blocking antibody, appears to be effective in identifying those results (more likely from poorly collected endocervical specimens) that are falsely positive, even in the presence of high concentrations of cross-reacting bacteria. Microscopic determination of endocervical specimen adequacy also may help to minimize false-positive (and false-negative) Chlamydiazyme results.

Confirmatory Testing Demonstrates That False-Positive Rates in the Chlamydiazyme Assay are Influenced by Gender and Genital Specimen Type

Chlamydia trachomatis antigen testing of clinical specimens is replacing culture as the test of choice. Because of a potential for false positive results in low prevalence populations, there is an apparent need for confirming specimens positive by enzyme immunoassay (EIA). To examine specimens falsely positive in the Chlamydiazyme EIA assay according to gender and specimen type. Testing of genitourinary specimens from men and women consecutively enrolled from five health care delivery sources in an urban Canadian population. All specimens were initially tested in the Chlamydiazyme test and all positives repeated in a confirmatory blocking assay provided by the manufacturer. Additional confirmatory testing was performed using immunofluorescence (IF) staining for C. trachomatis elementary bodies (EB's) and polymerase chain reaction (PCR). From Jan. 1, 1990 to June 1, 1991, multiple specimens from 656 men and 5,628 women of varying population prevalences were screened. EIA-positive specimens from women had a repeat negative rate of 22% to 27% from cervical swabs and 29% from urethral swabs. Male urethral swabs had a high repeat negative rate of 22% when EIA was the only positive test, but 2.4% when the specimen was positive by EIA and culture. EIA-positive first void urine (FVU) specimens from men had a repeat negative rate of 8.7% as opposed to 17% to 32% from women. Only 1.7% (2/115) of male FVU did not block compared to rates of 47% (22/47) to 80% (4/5) in FVU from women. Analysis of EIA optical densities (OD's) and EB counts showed an association between the absorbance range 0.1 to 1.4 OD and 0-85 EB's. The greatest number of EB's and highest OD's were seen with cervical specimens, followed by urine and urethral specimens in women infected at all three specimens. All 55 specimens that did not confirm in the blocking test had no EB's and a convenience sample of seven were negative by PCR. All of a subset of 50 blocked specimens contained EB's or were positive by PCR. Although a variable proportion of specimens may not repeat positive in the EIA, use of the blocking reagent to confirm the repeat positives is highly recommended and the rate of blocking may be heavily influenced by gender and specimen type.

Effect of endocervical specimen quality on detection of Chlamydia trachomatis and on the incidence of false-positive results with the Chlamydiazyme method

Duplicate endocervical swabs were collected from 1,675 patients to assess the effects of variations in specimen quality on Chlamydiazyme (Abbott Laboratories) detection of Chlamydia trachomatis and the incidence of false-positive results. One swab (at random) from each patient was tested for C. trachomatis antigen by using the standard Chlamydiazyme procedure. A 200-microliter volume of 0.9% saline was added to the other swab from each patient. After vortexing, 20 microliters was smeared on a slide for Papanicolaou (Pap) staining and the remaining specimen was then tested with the Chlamydiazyme assay. The Chlamydiazyme result was positive for 170 (10.1%) and 165 (9.8%) of the stained and unstained duplicate specimens, respectively (no significant difference). Pap stains on smears from 1,536 (91.7%) of the patients were analyzed, and endocervical and/or metaplastic (E-M) cells were detected in 789 (51.4%) smears. Of these 1,536 stained and analyzed specimens, 150 (9.8%) were Chlamydiazyme positive but only 132 (88.0%) of the positive results were confirmed by repeating the test and using a monoclonal blocking antibody (Abbott). Confirmed Chlamydiazyme-positive results were obtained from only 34 (4.6%) of 747 specimens lacking E-M cells but from 98 (12.4%) of 789 specimens containing the cells (P less than 0.001). Of the 150 initially Chlamydiazyme-positive results obtained with Pap-stained, analyzed specimens, 12 (26.1%) of 46 were falsely positive from specimens lacking E-M cells but only 6 (5.8%) of 104 were falsely positive from specimens containing E-M cells (P less than 0.01). C. trachomatis antigen was detected significantly more frequently and false-positive results were significantly less common from specimens in which E-M cells were detected.

Comparison of Chlamydial Culture with Chlamydiazyme Assay During Erythromycin PCE Treatment of Chlamydia Genital Infections

We compared chlamydial culture with the chlamydial antigen detection enzyme immunoassay system (Chlamydiazyme, Abbott Diagnostic Products; Abbott Park, IL) during treatment of Chlamydia genital infections. Participants received 333 mg of erythromycin PCE (Abbott Laboratories; Abbott Park, IL) 3 times per day for 7 days. On days 0, 3, 7, and 14, chlamydial cultures were positive in 30/30 (100%), 5/29 (17.2%), 0/27, and 0/25 participants, respectively. Concurrent Chlamydiazyme assays were positive in 30/30 (100%), 11/30 (37%), 1/28 (4%), and 0/25 participants. Twenty-eight of 28 persons who received erythromycin PCE for at least 3 days had negative test results for both chlamydial culture and Chlamydiazyme at their last clinic visit. Chlamydiazyme assay tended to remain positive longer than chlamydial culture during treatment, but 7 days after therapy was completed, no Chlamydia trachomatis antigens were detectable by this assay. Erythromycin PCE was well tolerated and rapidly eliminated Chlamydia genital infections in 83% of persons showing negative cultures by the third day of therapy.

Comparison of Chlamydial Culture with Chlamydiazyme Assay During Erythromycin PCE Treatment of Chlamydia Genital Infections

Comparison of Chlamydial Culture with Chlamydiazyme Assay During Erythromycin PCE Treatment of Chlamydia Genital Infections

Efficacy of duplicate genital specimens and repeated testing for confirming positive results for chlamydiazyme detection of Chlamydia trachomatis antigen.

In an attempt to increase Chlamydiazyme (Abbott Laboratories) detection of Chlamydia trachomatis antigen and to establish the reproducibility of positive results, we carried out an investigation into the usefulness of testing duplicate specimens, of more aggressive endocervical specimen collection by using cytobrushes instead of swabs, and of the repeated testing of both specimens from patients with one or two positive results. Duplicate endocervical (female) and urethral (male) specimens, including one swab and one cytobrush specimen from 1,331 nonpregnant women, were collected from symptomatic and asymptomatic patients. Specimens were transported and tested for C. trachomatis antigen as specified by the manufacturer. Tests on all specimens from patients with positive results were repeated. Antigen was initially detected in one or both specimens from 210 (10.7%) of 1,968 patients, and repetition of the tests confirmed its presence in 198 (10.1%) of the patients, including all 183 patients in whom it was initially detected in both specimens. Initial results from at least 8 of the 12 patients with irreproducible antigen detection were most probably falsely positive. Results from 21 (10.6%) of the 198 patients for whom antigen detection was confirmed were repeatedly positive on only one specimen (9 [4.5%] on the second of the two specimens collected). Of 115 women from whom one swab and one cytobrush sample were taken and who had repeatedly positive results, antigen was detected in 7 (6.1%) only on the swab sample and in 4 (3.5%) only on the cytobrush sample. Use of the cytobrush does not appear justified with the Chlamydiazyme assay, and collection of duplicate specimens provided only a modest increase in detection of C. trachomatis. However, repeated testing of specimens when results from only one of two specimens are positive appears to be of clinical value.

Detection of Chlamydia trachomatis in genital specimens by the Chlamydiazyme test.

Cotton swabs were used to collect two specimens each from 416 patients (206 males, 210 females) attending a sexually transmitted disease clinic. The first swab was transported in Specimen Storage Reagent and extracted in Specimen Dilution Buffer for enzyme immunoassay by Chlamydiazyme (Abbott Laboratories); the second swab was extracted into 2SP and inoculated into McCoy cell cultures. In the first phase of the study (215 patients: 111 males, 114 females) enzyme immunoassay results were positive (optical density greater than or equal to 0.1) in 30 of 35 instances in which Chlamydia trachomatis was isolated (sensitivity, 86%). Of 18 false-positive enzyme immunoassay results, 15 (83%) were cervical swabs (specificity, 90%). In a phase II study, using a modified Chlamydiazyme kit, 201 patients were tested (95 males, 106 females). Of 41 chlamydial isolates, 8 were not detected by the Chlamydiazyme test (sensitivity, 81%). Only three positive Chlamydiazyme test results could not be confirmed by culture (specificity, 98%). Overall, Chlamydiazyme assay provided a rapid (4 h), sensitive, and specific assay for the detection of chlamydial antigens.