Comparison of a fluorescent monoclonal antibody assay and a tissue culture assay for routine detection of infections caused by Chlamydia trachomatis

Evaluation of the Biostar Chlamydia OIA assay with specimens from women attending a sexually transmitted disease clinic

Chlamydia trachomatis infections are the most prevalent sexually transmitted diseases (STDs) in the United States. In acute-care settings such as clinics and emergency rooms, a desirable chlamydia screening assay should exhibit good sensitivity and good specificity and should provide test results while the patient is still present. The Biostar Chlamydia OIA (Biostar, Inc., Boulder, Colo.) is an optical immunoassay (OIA) that provides test results in less than 30 min and that uses a test format that allows office-based testing. This assay is performed entirely at room temperature without the need for rotators or other specialized equipment. The goal of this study was to compare the performance of the Biostar Chlamydia OIA for the detection of C. trachomatis with the performance of cell culture, direct fluorescent-antibody (DFA) assay (Syva MicroTrak; Syva Co., Palo Alto, Calif.), and PCR (Roche Amplicor Chlamydia trachomatis; Roche, Branchburg, N.J.) for the detection of C. trachomatis infections in women attending an urban STD clinic. For calculations of relative test performance (sensitivity, specificity, and positive and negative predictive values), patient specimens that yielded positive results by two or more of the four assays (cell culture, DFA assay, PCR, and OIA) were classified as "true infections." By these criteria, 42 of 306 total specimens were classified as positive for C. trachomatis (positive prevalence, 13.7%), 11 (3.6%; 10 by PCR and 1 by DFA assay) were positive by a single assay, and 253 (82.7%) were negative by all four tests. All culture-positive specimens were also positive by at least one other assay. Among the culture-negative specimens, 14(5%) specimens were positive by two of the three non-culture-based assays used. By using the criterion that positivity by at least two of the tests indicated a true infection,the relative sensitivities were as follows: culture and PCR, 92.9% each; Biostar Chlamydia OIA, 73.8%; and DFA assay, 59.5%.

Diagnosis by AMPLICOR PCR of Chlamydia trachomatis infection in urine samples from women and men attending sexually transmitted disease clinics

Screening of urine specimens from men for Chlamydia trachomatis infection by a commercial PCR assay (AMPLICOR C. trachomatis Test; Roche Diagnostic Systems, Inc., Branchburg, N.J.) is a sensitive and specific noninvasive diagnostic assay. Since screening of women for C. trachomatis infection with the AMPLICOR C. trachomatis Test has been limited to use with endocervical swab specimens, we conducted an evaluation of the AMPLICOR C. trachomatis Test for the detection of C. trachomatis using female urine samples and compared the results of those obtained by in vitro culture and PCR of endocervical swab specimens. For 713 men we compared the performance of AMPLICOR C. trachomatis Test with urine specimens with that of culture of urethral specimens. For specimens that were PCR positive and culture negative, two additional tests were used to resolve the discrepancies: direct fluorescent-antibody assay (DFA) of sediment from a spun endocervical specimen culture vial and major outer membrane protein-based PCR of the sediment from the endocervical specimen culture vial. Of 525 urine specimens from females, 67 (12.8%) were PCR positive, and 41 (7.8%) endocervical specimens from the 525 women were culture positive. After resolution of the discrepancies, the resolved sensitivity of the urine PCR was 93.3%, whereas the sensitivity of endocervical swab specimen culture was 67.3%. Of 468 female endocervical swab specimens, 47 (10.0%) had a positive PCR result and 33 (7.0%) were culture positive. The resolved sensitivity of the endocervical swab specimen PCR was 86%. Of 415 matched female urine and endocervical swab specimens, there were 49 confirmed infections; 30 (61.2%) specimens were positive by culture of the endocervical swab specimen, 40 (81.6%) were positive by confirmed endocervical swab specimen PCR, 43 (87.8%) were positive by confirmed urine PCR, and all 49 (100%) were positive by either endocervical swab specimen PCR or urine PCR. For men, the resolved sensitivity of the urine PCR was 88%, and the sensitivity of culture was only 50.7%. These results indicate that urine PCR is highly sensitive for the detection of C. trachomatis in both women and men and provides a noninvasive technique for routine screening for chlamydial infection.

Diagnosis of Chlamydia trachomatis genitourinary infection in women by ligase chain reaction assay of urine

Genitourinary infection with Chlamydia trachomatis is a common and potentially serious sexually transmitted disease. Diagnosis of C trachomatis infection in women typically relies on culture of endocervical swabs, an invasive and expensive procedure. The ligase chain reaction (LCR) is an in-vitro nucleic acid amplification technique that exponentially amplifies selected DNA sequences. We have compared an LCR-based assay to detect C trachomatis plasmid DNA in first void urine with culture of endocervical swabs for matched specimens from 1937 women from four geographic regions. Discordant specimen pairs were further tested by direct fluorescent antibody staining for elementary bodies and an alternative LCR assay based on the chlamydial outer membrane protein gene. An "expanded gold standard" was defined to include all culture-positive as well as culture-negative, confirmed LCR-positive women. The sensitivity and specificity of the LCR assay with first void urine samples compared with the expanded gold standard were 93.8% and 99.9%, respectively; the corresponding values for culture were 65.0% and 100%, respectively. Thus, an automated LCR assay of readily obtained urine samples showed a detection rate for infected women almost 30% greater than that of endocervical swab culture. The LCR assay was highly effective for the detection of C trachomatis in urine from women with or without signs or symptoms of chlamydial genitourinary tract infection.

Detection of Chlamydia trachomatis antigens in first-void urine to identify asymptomatic male carriers

Early morning first-void urine collected from 279 sexually active Swedish male recruits (mean age 19.5 years) was tested by two commercial enzyme immunoassay (EIA) kits, MicroTrak and IDEIA III, and by MicroTrak direct fluorescence assay (DFA), to detect Chlamydia trachomatis antigens. A result was assumed to be true-positive when any of the two non-culture tests were positive for the same specimen. In one case where only DFA was positive, confirmatory chlamydial testing was performed by isolating the organism from a urethral swab. On these premises, the number of true-positive men was 26 (9.3% of all men studied). The sensitivity, specificity, positive predictive value and negative predictive value for MicroTrak EIA were 85%, 98%, 85%, and 98%, respectively. IDEIA III was less sensitive than MicroTrak EIA (42% vs 85%). In conclusion, the diagnosis of asymptomatic chlamydial infections in men can be established with reasonable accuracy by the detection of Chlamydia antigens in urine samples using MicroTrak EIA.

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.

Age and sex correlation of Chlamydia trachomatis infections evaluated by the culture technique and by an enzyme immunosorbent assay, IDEIA

A total number of 1358 patients were examined for genital infections with Chlamydia trachomatis. 252 urethral smears from men and 1106 cervical smears from women were obtained. The average age of infected patients was 24.8 years (females 24.1, males 27.7). The overall prevalence was 10.6% (females 10.0%, males 13.1%). At the age below 20 years, the prevalence was 21% for both women and men, and 25% when data were restricted to patients consulting general practitioners. Above that age the overall prevalence was lower in all age intervals, and higher among males than females. All samples were tested by the tissue-culture technique, and the results were confirmed by the IDEIA (Boots-Celltech) enzyme-linked immunosorbent assay kit (EIA) for detection of C. trachomatis. The original smear was used for both culture and EIA. The EIA test was evaluated to have a sensitivity of 90.8% and a specificity of 95.4% when using a cut-off level of 0.05 mean extinction values (MEV), as described by the manufacturer.

Comparison of three non-culture techniques for detection of Chlamydia trachomatis in genital tract specimens

A direct immunofluorescence (DIF) technique (Imagen) and two enzyme immunoassay (EIA) techniques (Chlamydiazyme and IDEIA) were compared for the detection of Chlamydia trachomatis in genital specimens from 502 attenders at a genitourinary medicine clinic. Eighty-two attenders were regarded as infected: 67 with positive results by at least two of the three techniques and 15 by virtue of elementary bodies detected in stored EIA buffer samples. With a positivity criterion of greater than or equal to 6 bodies Imagen was 76% sensitive for men and 61% sensitive for women. The sensitivity of Chlamydiazyme was 73% for men and 90% for women; comparative values for IDEIA were 80% and 71%, respectively. All three techniques were over 98% specific. Sampling order appeared to influence the sensitivity of IDEIA for specimens from men. All three techniques were less sensitive in the absence of cervicitis. The performances of the EIA techniques compared favourably with that of the more established technique of DIF.

A rapid monoclonal immunofluorescence assay for Chlamydia psittaci in fecal smears from psittacine birds

One hundred two fecal specimens from psittacine birds submitted to Veterinary Laboratory Services of the California Department of Food and Agriculture at Petaluma were screened for Chlamydia psittaci by a direct immunofluorescence assay using a fluorescein-labeled monoclonal antibody conjugate specific for Chlamydia sp. Results were compared with those obtained by isolation of chlamydia in cultures of McCoy mouse cells. The relative specificity of the direct fluorescent antibody test on fecal smears was 98.9% and the relative sensitivity was 62.5%. The results of this study suggested that the direct fluorescent antibody test was highly specific, and it proved to be a useful same-day antemortem diagnostic test for birds with symptomatic chlamydial infection. The use of centrifugation in the cell culture assay was found to significantly enhance the level of chlamydial infection in cell culture.

Laboratory diagnosis of human chlamydial infections

Chlamydia trachomatis is a human pathogen that causes ocular disease (trachoma and inclusion conjunctivitis), genital disease (cervicitis, urethritis, salpingitis, and lymphogranuloma venereum), and respiratory disease (infant pneumonitis). Respiratory chlamydioses also occur with infection by avian strains of C. psittaci or infection by the newly described TWAR agent. Diagnosis of most acute C. trachomatis infections relies on detection of the infecting agent by cell culture, fluorescent antibody, immunoassay, cytopathologic, or nucleic acid hybridization methods. Individual non-culture tests for C. trachomatis are less sensitive and specific than the best chlamydial cell culture system but offer the advantages of reduced technology and simple transport of clinical specimens. Currently available nonculture tests for C. trachomatis perform adequately as screening tests in populations in which the prevalence of infection is greater than 10%. A negative culture or nonculture test for C. trachomatis does not, however, exclude infection. The predictive value of a positive nonculture test may be unsatisfactory when populations of low infection prevalence are tested. Tests that detect antibody responses to chlamydial infection have limited utility in diagnosis of acute chlamydial infection because of the high prevalence of persistent antibody in healthy adults and the cross-reactivity due to infection by the highly prevalent C. trachomatis and TWAR agents. Assays for changes in antibody titer to the chlamydial genus antigen are used for the diagnosis of respiratory chlamydioses. A single serum sample that is negative for chlamydial antibody excludes the diagnosis of lymphogranuloma venereum.

Detection of Chlamydia trachomatis. A study of the direct immunofluorescence technique and a review diagnostic limitations

Because of the high prevalence of Chlamydia trachomatis in adolescent females and the high cost of chlamydia cultures, we evaluated the use of the direct fluorescein conjugated monoclonal antibody test (DFA) in diagnosing C. trachomatis in adolescent females. Chlamydia trachomatis was found in 37 (20.1%) of 184 cultures. The sensitivity of the direct smear as compared with the culture was 89% and the specificity was 99%. The results of recent studies of the DFA and chlamydiazyme tests are reviewed as well as the problems in comparing techniques.

Detection of Chlamydia trachomatis in culture and urogenital smears by in situ DNA hybridization using a biotinylated DNA probe

The detection of Chlamydia trachomatis by in situ DNA hybridization in urogenital smears was investigated using a commercially available biotinylated DNA probe. Intracellular staining of inclusion bodies was used as the criterion for positivity. Of 35 patients with a culture proven chlamydial infection 19 had smears in which C. trachomatis was detected by in situ DNA hybridization, indicating a sensitivity of 54%. Of 57 patients with a negative culture, two had positive smears by in situ DNA hybridization. To compare whether the criterion for positivity had influenced the sensitivity obtained with in situ DNA hybridization, 14 duplicate smears from culture positive patients were analysed with in situ DNA hybridization and immunofluorescence. Both methods detected intracellular inclusion bodies in seven of these smears, suggesting that the presence of infected cells mainly determines the sensitivity. The DNA probe did not cross-react with micro-organisms commonly found in the urogenital tract.

Comparison of three techniques for detection of Chlamydia trachomatis in endocervical specimens from asymptomatic women

Culture in DEAE-dextran-treated HeLa 229 cells, a solid-phase enzyme immunoassay (EIA) (Chlamydiazyme; Abbott Laboratories, North Chicago, Ill.), and a direct immunofluorescence test (DFA) (MicroTrak; Syva Co., Palo Alto, Calif.) were compared for the detection of Chlamydia trachomatis in endocervical specimens from 715 asymptomatic women. Response to antibiotic therapy was also monitored at least 4 weeks after completion of therapy. An additional sample was collected at a control visit, and a second culture was performed if discrepancies were observed between the three tests. A total of 48 infections were diagnosed, for a prevalence of 6.7%. At the first visit, 37 specimens were positive by culture. The respective sensitivities of EIA and DFA were 78.4 and 81.1% and the respective specificities were 96.8 and 97.9% when compared with the cell culture technique. The positive predictive values were 56.9 and 68.2%, respectively. When the additional 11 infections detected by the second culture were included to establish a new standard of positivity, the sensitivity of the first culture was estimated at 77.1%. The positive predictive values of EIA and DFA increased to 77.6 and 83.7%, respectively. EIA and DFA performed as well as culture for control of therapy; a 100% agreement among the three techniques was observed.

Assessment of enzyme immunoassay and immunofluorescence tests for detection of Chlamydia trachomatis

Two rapid diagnostic tests for Chlamydia trachomatis (Microtrak, Syva Co., Palo Alto, Calif.; and Chlamydiazyme, Abbott Laboratories, North Chicago, Ill.) were evaluated in comparison with growth of the organism in tissue culture for 2,030 urogenital specimens from men and women. Neither test performed as well as culture, which detected 296 of 310 positive specimens. The overall sensitivity and specificity for Microtrak were 73 and 99%; corresponding values for Chlamydiazyme were 83 and 98%. The majority of false-negative results with both rapid tests occurred when cultures contained less than 10 inclusions per cover slip. There were also areas of unconfirmed reactivity for both tests that led us to suggest that a reporting category of "suspicious" be developed for certain test results. For Microtrak, the suspicious result is a slide containing fewer than 10 elementary bodies; for Chlamydiazyme, it is any absorbance reading less than 0.4. Creation of a "suspicious" category would lower the sensitivity for Chlamydiazyme considerably, to 64%, and increase the positive predictive value for females to 95%. Although this may result in the underreading of some specimens from males, the tests could then be used with greater confidence in females for whom testing is essential for appropriate treatment.