Improved sensitivity of an enzyme immunoassay IDEIA for detecting Chlamydia trachomatis

Evaluation of the microparticle enzyme immunoassay Abbott IMx Select Chlamydia and the importance of urethral site sampling to detect Chlamydia trachomatis in women

OBJECTIVE

To evaluate the commercial microparticle enzyme immunoassay (MEIA), Abbott IMx Select Chlamydia, for the detection of Chlamydia trachomatis in women and to compare its performance with endocervical cell culture. Also, to determine whether sampling the urethral site is an important part of chlamydial diagnosis in women.

SETTING

The Auckland, Manukau, and Waitakere Sexual Health Clinics, Auckland, New Zealand and the Department of Clinical Microbiology, Auckland Hospital, Auckland, New Zealand.

PATIENTS

The study population consisted of 622 consecutive women who attended the three sexual health clinics.

METHODS

The IMx Chlamydia assay was performed on an IMx analyser, following a specimen treatment procedure. All reactive samples from the IMx Chlamydia assay were confirmed using the IMx Chlamydia blocking antibody reagent. The Syva direct fluorescent antibody (DFA) test was used to aid in resolving discrepancies. The cell culture technique was performed in shell vials using cycloheximide treated McCoy cells, which were stained using a fluorescein conjugated monoclonal antibody.

RESULTS

When compared against the endocervical cell culture, the IMx Chlamydia had a sensitivity of 82.1% (23/28) and a specificity of 99.3% (590/594). When compared against an expanded gold standard, the IMx Chlamydia and endocervical cell culture had sensitivities of 84.4% (27/32) and 87.5% (28/32), specificities of 100% (590/590) and 100% (590/590), positive predictive values of 100% (27/27) and 100% (28/28), negative predictive values of 99.2% (590/595) and 99.3% (590/594), and accuracies of 99.2% (617/622) and 99.4% (618/622), respectively. The prevalence rate by endocervical cell culture and the expanded gold standard were 4.5% and 5.1%, respectively. Additional urethral cell culture testing revealed a further nine patients positive from this site only, giving a 28% (9/32) increase in the number of patients diagnosed for chlamydia, thus giving an overall prevalence of 6.6% (41/622).

CONCLUSIONS

The IMx Chlamydia assay is an easy and rapid test to perform, it is cost effective, and shows similar performance to endocervical cell culture in the female population studied and is thus an excellent alternative to culture for the diagnosis of C trachomatis. The study also showed the importance of urethral site sampling in these women, as endocervical testing alone will underestimate the prevalence of chlamydial genital infection.

Evaluation of a commercial polymerase chain reaction assay for Chlamydia trachomatis and suggestions for improving sensitivity

A commercial polymerase chain reaction (PCR) assay (Amplicor, Roche) for Chlamydia trachomatis was compared with a direct fluorescent antibody (DFA) test using urethral and cervical samples, many of which on the basis of prior testing by DFA contained small rather than large numbers of elementary bodies. Urine samples were collected from patients in a sequential unselected manner. Of 244 clinical specimens (138 male urethral and cervical; 106 male and female urine), 66 were positive by both DFA and PCR and 141 were negative by both tests. Nine samples were DFA negative and PCR positive, and 28 samples were DFA positive and PCR negative. However, 24 (86%) of the latter samples contained fewer than ten elementary bodies. When serial dilutions of laboratory stock strains (serovars E and H) were tested, the DFA test detected Chlamydia trachomatis at a dilution tenfold greater than the PCR. Furthermore, of five DFA-positive clinical samples, three that were PCR negative when tested according to the manufacturer's instructions were positive when they were diluted less. A modification of the PCR assay along these lines might improve sensitivity.

Detection of amplified Chlamydia trachomatis DNA using a microtiter plate-based enzyme immunoassay

A microtiter plate-based method to detect amplified DNA was developed. The method uses on biotin-labeled primer in the polymerase chain reaction (PCR) mixture. The labeled amplicon is bound to streptavidin-coated microtiter plates, denatured and hybridized to a digoxigenin-labeled probe. The specificity of the hybridization reaction was optimized by varying the temperature of the subsequent washing step and adding urea to the washing buffer. The digoxigenin label was detected using an enzyme immunoassay (EIA). This PCR-EIA was compared with a standard PCR assay that uses gel electrophoresis, blotting and hybridization to detect the amplicon, with isolation in cell culture, and with an antigen detection EIA (Chlamydiazyme) in the diagnosis of Chlamydia trachomatis infection in 309 female patients attending a sexually transmitted diseases outpatient clinic. The prevalence of Chlamydia trachomatis infection as determined by isolation in cell culture, EIA, PCR-EIA and standard PCR assay was 9.1%, 8.7%, 12.3%, and 12.9%, respectively. Compared with results of a reference set of confirmed-positive cases (defined by a positive result in two or more independent assay after analysis of discrepancies), the sensitivity and specificity was 71.1% and 99.6% for cell culture, 65.8% and 99.3% for the EIA, 92.1% and 98.9% for the PCR-EIA, and 97.4% and 98.9% for the standard PCR assay. It is concluded that the PCR-EIA described is a fast, sensitive and specific method for detecting Chlamydia trachomatis in clinical specimens.

Limited value of two widely used enzyme immunoassays for detection of Chlamydia trachomatis in women

Enzyme immunoassays (EIAs) are widely used to diagnose chlamydial infections in patients attending genitourinary medicine clinics. They are relatively easy to perform and are suitable for testing large numbers of samples. The objective of this study was to determine what proportion of women with chlamydial infection, defined as the presence of Chlamydia trachomatis in a cervical smear or deposit and/or in the urinary tract, detected by means of a sensitive direct fluorescent antibody test could also be identified by using two commercially available EIAs to test cervical samples. On hundred fifty-one women attending the genitourinary medicine clinic at St. Mary's Hospital, London, were enrolled. The use of the Chlamydiazyme (Abbott Diagnostics, UK) and MicroTrak (Syva, UK) EIAs resulted in the identification of only 56% and 63%, respectively, of women with chlamydial infection detected by direct fluorescent antibody staining. Thus, the EIAs available for detection of chlamydiae in cervical samples are inadequate for identifying all infected women. Improvement might be achieved by testing multiple samples or by resorting to tests of greater sensitivity.

Evaluation of five immunoassays for detection of Chlamydia psittaci in cloacal and conjunctival specimens from turkeys

Five commercially available immunoassays were evaluated for the detection of Chlamydia psittaci in cloacal and conjunctival swabs from industrially raised turkeys: IMAGEN (DAKO Diagnostics, Ely, Cambridgeshire, United Kingdom), Chlamydia CEL-VET IF (Cellabs, Brookvale, Australia), IDEIA (DAKO Diagnostics), CELISA (Cellabs), and CLEARVIEW (Unipath, Bedford, United Kingdom). Results were compared with isolation in Buffalo Green Monkey cells as a reference method. For the conjunctival samples, the sensitivities of the IMAGEN test, the Chlamydia CEL-VET IF test, the IDEIA, the CELISA, and the CLEARVIEW test were found to be 100, 66, 0, 0, and 0%, respectively, as compared to the reference test. Also for the conjunctival samples, the specificities of the IMAGEN test, the Chlamydia CEL-VET IF test, and the IDEIA were found to be 100, 11, and 92.8%, respectively. For the cloacal specimens, the sensitivities of the IMAGEN test, the Chlamydia CEL-VET IF test, the IDEIA, the CELISA, and the CLEARVIEW test were found to be 100, 93.3, 26.6, 0, and 53.3%, respectively. Also for the cloacal specimens, the specificities of the IMAGEN test, the Chlamydia CEL-VET IF test, the IDEIA, and the CLEARVIEW test were found to be 92, 12, 100, and 88%, respectively. The IMAGEN test was the most sensitive and specific direct chlamydia antigen detection test for cloacal and conjunctival samples from turkeys.

Evaluation of sensitivity of 10 diagnostic assays for Chlamydia trachomatis by use of a simple laboratory procedure

AIMS

To determine the sensitivity of commercially available diagnostic assays for Chlamydia trachomatis using a simple method.

METHODS

Nine commercial assays and an "in-house" polymerase chain reaction (PCR) were evaluated using serial dilutions of a laboratory grown H serovar--four of them using a laboratory grown E serovar. Seven of the assays were further tested using dilutions of several cervical samples known to contain chlamydiae.

RESULTS

The most sensitive assays were the MicroTrak direct fluorescent antibody (DFA) test (Syva) and the PCR which detected C trachomatis at a 10(-8) dilution of the H serovar, while the two least sensitive, Clearview (Unipath) and TestPack (Abbott), were positive only at 10(-4) and 10(-3) dilutions, respectively. A range of enzyme immunoassays (EIAs) and a nucleic acid hybridisation test were of intermediate sensitivity. The results with serovar E were consistent with these. When clinical samples were examined, the DFA test detected C trachomatis in dilutions at least 10-fold greater than any other assay.

CONCLUSIONS

The range of sensitivity of diagnostic assays determined by the laboratory dilution procedure is very wide. Sensitivity assessed in this way, however, reflects the ability of the assays to detect C trachomatis in large scale clinical trials. The dilution procedure, which is simple to undertake, could therefore be applied by any laboratory before a new diagnostic method is considered for routine use.

Evaluation of sensitivity of 10 diagnostic assays for Chlamydia trachomatis by use of a simple laboratory procedure

AIMS

To determine the sensitivity of commercially available diagnostic assays for Chlamydia trachomatis using a simple method.

METHODS

Nine commercial assays and an "in-house" polymerase chain reaction (PCR) were evaluated using serial dilutions of a laboratory grown H serovar--four of them using a laboratory grown E serovar. Seven of the assays were further tested using dilutions of several cervical samples known to contain chlamydiae.

RESULTS

The most sensitive assays were the MicroTrak direct fluorescent antibody (DFA) test (Syva) and the PCR which detected C trachomatis at a 10(-8) dilution of the H serovar, while the two least sensitive, Clearview (Unipath) and TestPack (Abbott), were positive only at 10(-4) and-3 dilutions, respectively. A range of enzyme immunoassays (EIAs) and a nucleic acid hybridisation test were of intermediate sensitivity. The results with serovar E were consistent with these. When clinical samples were examined, the DFA test detected C trachomatis in dilutions at least 10-fold greater than any other assay.

CONCLUSIONS

The range of sensitivity of diagnostic assays determined by the laboratory dilution procedure is very wide. Sensitivity assessed in this way, however, reflects the ability of the assays to detect C trachomatis in large scale clinical trials. The dilution procedure, which is simple to undertake, could therefore be applied by any laboratory before a new diagnostic method is considered for routine use.

Noninvasive detection of Chlamydia trachomatis in men: a comparison of two immunoassay tests

This investigation compared a rapid enzyme immunoassay test and an enzyme-amplified immunoassay test with culture for the noninvasive detection of Chlamydia trachomatis urethritis in men. Urine specimens from 108 male subjects were evaluated for the presence of C trachomatis antigen, using the Kodak Surecell Chlamydia rapid enzyme immunoassay test and IDEIA Chlamydia enzyme-amplified immunoassay test. The test results were then compared with urethral C trachomatis culture and urethral Gram's stain analyses. Performance characteristics of the two tests were similar. The rapid chlamydial enzyme immunoassay test demonstrated several clinical advantages. Appropriate use of these tests may decrease patient morbidity and clarify organism etiology for enhanced specific medical care of urethritis in men.

Evaluation of Pharmacia Chlamydia EIA for diagnosis of genital infections caused by Chlamydia trachomatis

A new enzyme-immunoassay test (EIA), Pharmacia Chlamydia EIA, was evaluated in comparison with isolation in cell culture for the diagnosis of genital infections caused by Chlamydia trachomatis. Endocervical and endourethral specimens were collected from 913 patients (875 female and 38 male patients respectively). Sensitivity, specificity, positive predictive and negative predictive values for this test were 89.4%, 99.2%, 85.8% and 99.4% respectively. Where discrepancies between the 2 techniques occurred, the remainder of the EIA buffer was stained for chlamydial antigen by direct immunofluorescence using the Syva Microtrak Chlamydia trachomatis Direct Specimen Test. Laboratory strains of various micro-organisms that may be present in genital specimens did not cross react with the EIA test except for Staphylococcus aureus and Group B Streptococcus at very high concentrations. The Pharmacia Chlamydia EIA is suitable for a laboratory which handles a large number of chlamydial specimens daily. However, when interpreting EIA results, the prevalence of chlamydial infection in the patient population should be established. At present, EIA tests are unsuitable as the only test for chlamydial diagnosis in low risk populations.

Evaluation of the polymerase chain reaction (PCR) for detection of Chlamydia psittaci in abortion material from ewes

The polymerase chain reaction (PCR) was evaluated as a diagnostic tool for detection of Chlamydia (C.) psittaci in abortion material from 40 ewes. For this purpose, PCR results of 87 samples were compared with direct microscopic identification after chemical staining, cell culture isolation and a commercially available enzyme-linked immunosorbent assay (ELISA). The value for sensitivity as compared to cell culture was 97.7% whereas the specificity-value was calculated to be 84.1%.

Development and clinical evaluation of a polymerase chain reaction test for detection of Chlamydia trachomatis

A polymerase chain reaction (PCR) for the detection of Chlamydia trachomatis was developed and evaluated. Two primer-probe sets were designed; one detected a specific sequence of the plasmid, and the other detected the gene encoding the major outer membrane protein. Both sets reacted species specifically and amplified sequences from all human serovars. A simple protocol was used for sample pretreatment. The PCR was optimized by addition of tetramethylammonium chloride and bovine serum albumin. The results of the PCR with the plasmid primer-probe set were compared with those of culture and the Chlamydiazyme and Gen-Probe PACE 2 tests for urogenital specimens from 220 patients. The rates of prevalence of infection with C. trachomatis were 22.7, 16.4, 15.0, and 14.5%, respectively. The sensitivities of the Chlamydiazyme and Gen-Probe PACE 2 assays compared with culture were 66.7 and 61.1%, respectively, and their sensitivities compared with PCR were 60.0 and 60.0%, respectively. The sensitivity of culture compared with PCR was 70.0%. Forty-eight of the 50 specimens positive by PCR with the plasmid primer-probe set could be confirmed by PCR with the major outer membrane protein primer-probe set or culture. It is concluded that the PCR is the most sensitive technique for laboratory detection of C. trachomatis.

Monoclonal antibody based capture ELISA/ELIFA for the detection of Chlamydia psittaci in veterinary clinical specimens

A capture ELISA/ELIFA system based on monoclonal capture and biotinylated monoclonal detection antibody with specificity for an epitope on chlamydial lipopolysaccharide (LPS) is described. The assay is fast, specific and detects a minimum dose of approximately 2000 chlamydial particles (C. psittaci). Unlike other commercially available test kits, it comprises a proteinase K treatment to exclude non-specific binding of antibodies to Fc receptors. In contrast to the sophisticated and cumbersome isolation procedures, even non-specialized laboratories may use this assay system for the investigation of clinical samples of different origin for the presence of C. psittaci within a short period of time. Due to the genus specificity of the monoclonal antibody used C. trachomatis and C. pneumoniae can be detected as well.

Laboratory techniques for the diagnosis of chlamydial infections

Yolk-sac inoculation of embryonated eggs was superseded 25 years ago by the use of cell cultures (often McCoy) for the isolation of Chlamydia trachomatis. Centrifugation of specimens onto the cell monolayers was shown to increase sensitivity, but little of late has further improved sensitivity which is at least ten-fold greater than that of eggs. However, culture is slow and labour intensive so that non-cultural techniques without these drawbacks have come to dominate. Direct fluorescent antibody (DFA) tests are rapid and have sensitivities that range from 70% to 100% for men and 68% to 100% for women, and specificities that range from 87% to 99% for men and 82% to 100% for women; if the tests are read by competent observers the values are at the top end of the ranges. The detection rate may be enhanced even further by relatively low-speed centrifugation of specimens before staining. Skilled reading is not a feature of enzyme immunoassays (EIAs) which according to the literature have sensitivities that range from 62% to 97% for men and 64% to 100% for women, and specificities that range from 92% to 100% for men and 89% to 100% for women. However, comparison against poor reference tests is responsible for most of the higher values and the clinician should not be misled into believing that EIAs have excellent sensitivity; the lower values in the ranges are closer to reality. Furthermore, EIAs that are being designed for use by general practitioners should be regarded with the greatest caution since lack of sensitivity means that chlamydia-positive patients will go undetected. The polymerase chain reaction (PCR) is not bedevilled by insensitivity but it is no more sensitive than the most sensitive cell culture or DFA tests. PCR is unsuitable for routine diagnosis but has a place as a research tool. For men, examination of "first-catch" urine samples by the best of the non-cultural procedures provides an acceptable non-invasive approach to diagnosis; for women, the value of examining urine may be less, but needs to be thoroughly tested. However, there is little doubt that a Cytobrush used to obtain cervical specimens holds no practical advantage over a swab. Serological tests are reliant on the provision of paired sera for making a diagnosis; high antibody titres in single sera may be suggestive of an aetiological association in deep-seated chlamydial infections (epididymitis, arthritis, salpingitis, etc), but unequivocal interpretation is unusual, particularly in an individual case, since the distinction between a current and past infection is problematical.

The value of urine samples from men with non-gonococcal urethritis for the detection of Chlamydia trachomatis

Chlamydia trachomatis was sought at first and subsequent clinic visits in urethral swabs and urines from 112 heterosexual men with acute non-gonococcal urethritis (NGU). In comparison with a urethral swab tested by Micro Trak (MT), a urine deposit tested in the same way was 90% as sensitive. Examining a urine deposit by the enzyme immunoassay IDEIA was a little less sensitive (89%) than examining a similar deposit by MT, and was less sensitive (82%) than examining a urethral swab by MT. The results of testing urines were little influenced by collecting them either before or after swabbing the urethra, and there was evidence that examining all of a urine sample by IDEIA would have increased sensitivity. Overall, 55 (49%) of the men were diagnosed as C trachomatis-positive based on the results of testing both a urethral swab and a urine sample. Furthermore, a small numbers of chlamydiae were detected by examining urine by MT and, to a lesser extent, by IDEIA, so that there is no reason why this non-invasive approach should not be successful in men other than those with acute NGU.

Comparison of the Kallested Pathfinder EIA, cytocentrifuged direct fluorescent antibody, and cell culture for the detection of Chlamydia trachomatis

A total of 203 duplicate endocervical samples collected from patients at an adolescent health care center were tested for the presence of Chlamydia trachomatis by cell culture, Pathfinder enzyme immunoassay (EIA) (Kallestad) and cytocentrifuged direct fluorescent antibody (DFA). Compared to cell culture, the Pathfinder assay demonstrated a sensitivity and specificity of 85.2% and 100%, whereas the DFA procedure demonstrated to be 92.6% sensitive and 99.4% specific.

A 2-year quantitative assessment of Chlamydia trachomatis in a sexually transmitted diseases clinic population by the MicroTrak direct smear immunofluorescence test

The MicroTrak direct smear immunofluorescence test was used to determine the prevalence of Chlamydia trachomatis elementary bodies (EBs) in groups of patients in various clinical categories, most of whom were seen in a clinic for sexually transmitted diseases (STD). Overall, 8138 adequate specimens were tested, of which 14.3% were found to contain chlamydial EBs. Of the samples from patients seen in the STD clinic, over 70% were from women and 14.9% of these were positive, as were 15.7% of those from men. EBs were detected in 27% of samples from infants and in 7.0% of those from adults with conjunctivitis. EBs were detected most often in men with nongonococcal urethritis (40.2%), infants with conjunctivitis (30%) and contacts of chlamydiae-positive patients (24.5%) and least often in 'prostatitis' (2.9%) and patients tested to determine the success of treatment (2.7%). Over 40% of samples from both the male urethra and the cervix contained 10 or fewer EBs, highlighting the importance of recognizing small numbers and the sensitivity required of other detection procedures.

Comparison of IDEIA III and cell culture for the detection of Chlamydia trachomatis in endocervical specimens

A total of 803 endocervical samples were obtained from females with clinical or epidemiological histories suggesting chlamydia infection. These specimens were tested by IDEIA III and cell culture for the presence of Chlamydia trachomatis. After resolution of discrepant results by direct fluorescent-antibody staining of pelleted cell culture transport materials, IDEIA III demonstrated sensitivity, specificity, and positive and negative predictive values of 93.8, 99, 92.9, and 99.1%, respectively.