Evaluation of the direct fluorescent antibody test for diagnosis of chlamydial infections

Chlamydia trachomatis in adolescents: a review

Genital infections caused by Chlamydia trachomatis represent the most prevalent bacterial sexually transmitted disease in the United States. An estimated 3-4 million cases annually necessitate the expenditure of more than $2 billion in health care costs per year. The ramifications of infection with this organism have significant reproductive complications. The objective of this paper is to provide the reader with a review of Chlamydia trachomatis in general with particular focus on those areas that are pertinent to the adolescent population. The authors hereby provide an overview of the clinically pertinent microbiology, epidemiology, risk factors, selective screening protocols, diagnostic methods, clinical manifestations, and sequelae of C. trachomatis.

Solid-phase C1q-directed bacterial capture followed by PCR for detection of Chlamydia trachomatis in clinical specimens

An antigen capture system based on the binding of bacteria to solid-phase immobilized complement C1q followed by PCR for detection of Chlamydia trachomatis in clinical samples was developed and clinically evaluated. Comparison of C1q-directed antigen capture PCR with cell culture and direct PCR on 71 consecutive clinical specimens revealed an identical sensitivity. In this group, all 11 cell culture-positive samples were positive by direct PCR and C1q-directed antigen capture PCR. In addition, two samples found negative by cell culture were found positive by both direct PCR and C1q-directed antigen capture PCR. To further assess the sensitivity of C1q-directed antigen capture PCR, 20 clinical samples with one to five inclusions in cell culture and 20 clinical samples with 6 to 20 inclusions in cell culture were tested. Results obtained showed sensitivities of 95 and 90% for clinical samples with 6 to 20 and 1 to 5 inclusions in cell culture, respectively. Using C1q-coated solid phases, C1q-binding Chlamydia particles can be concentrated from large volumes with concomitant removal of inhibitors of PCR, allowing the use of large volumes of clinical samples for clinical testing. Since C1q has been shown to bind to a range of gram-negative bacteria, the newly developed technique has utility for a broad range of bacteria.

Evaluation of two ELISA's for detecting Chlamydia trachomatis from endocervical swabs

Two enzyme immunoassays (EIAs) detecting Chlamydia trachomatis from endocervical swabs, Syva MicroTrak (MT) and Abbott Chlamydiazyme (CZ), were compared with a tissue culture (TC) standard. Initially, 8% (100 of 1250) of specimens were TC positive, yielding sensitivities of 94% (94 of 100) for MT and 79% (79 of 100) for CZ with identical 98% specificities (1129 of 1150 for MT and 1130 of 1150 for CZ). Discrepant specimens were retested by both EIAs and assayed for elementary bodies (EBs) by a fluorescent antibody test. After discrepancy analysis, 9.5% (118) of 1240 patients were either TC or EB positive, yielding sensitivities of 94.1% for MT (111 of 118) and 79.7% for CZ (94 of 118) with identical specificities of 100% (1122 of 1122). These results indicate that the MT is significantly more sensitive (p less than 0.05, McNemar test) than CZ in detecting C. trachomatis from endocervical swabs.

Comparison of three new nonculture tests in the diagnosis of Chlamydia genital infections

This study compares three new rapid nonculture tests to cell culture with passage for the diagnosis of Chlamydia genital infections in sexually active adolescent and young adult females. Two hundred consecutive patients having a pelvic examination had cervical samples taken for the following: Papanicolaou smear, gonorrhea culture, Chlamydia cell culture, direct fluorescent antibody (DFA; Difco), isotopic DNA probe (Gen-Probe), and enzyme immunoassay (EIA; IDEIA III, Novo BioLabs). After resolution of discrepant results, 25 of the specimens were judged to be positive. The DFA identified 17 of the 25, with 3 false-positive results; the DNA probe identified 20 of the 25, with no false positive results; and the EIA identified 22 of the 25, with one false-positive result. The sensitivities, specificities, and positive and negative predictive values, respectively, were DFA, 68%, 98.2%, 85%, 95.5%; DNA probe, 80%, 100%, 100%, 97.2%; and EIA, 88%, 99.4%, 95.6%, 98.3%. These new rapid nonculture tests are comparable and relatively reliable, with trends favoring the EIA and the DNA probe. Further studies with larger samples are needed to determine their clinical utility.

Accuracy of Chlamydia trachomatis antigen detection methods in a low-prevalence population in a primary care setting

We compared a direct fluorescent-antibody stain (DFA) and an enzyme immunoassay (EIA) with a standard cell culture technique for the detection of Chlamydia trachomatis infection in women in an urban family practice setting. We also evaluated a DFA sample in a commercial laboratory to determine the interlaboratory reliability of this test. There were 268 women in the study; the EIA provided a higher sensitivity (83 versus 50%) and a higher positive predictive value (83 versus 69%) than the DFA test and comparably high specificity (99 versus 98%). Concordance between the two laboratories on the DFA test was not high when data were adjusted for chance agreement (kappa coefficient = 0.64). DFA validity was optimal with an elementary body cutoff of greater than 5, while EIA validity was optimal at the recommended cutoff of 0.1 optical density unit. None of 11 women with negative cultures after treatment had false-positive antigen tests. False-negative results with both tests were associated with low culture inclusion counts but were not strongly associated with the presence or absence of symptoms, menses, pregnancy, or recent antibiotic use. False-positive results with EIA were seen only for three women who had a chief complaint of vaginal discharge. Although the positive predictive value of DFA could be increased in high-prevalence subpopulations, EIA was still more valid in two such groups: teenagers and prenatal patients. These results indicate that EIA might be preferable for low- or moderate-prevalence populations in primary care settings and that a falloff in DFA sensitivity could be explained by lower infection burdens in low-prevalence groups.

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 chemiluminescent DNA hybridization assay for the detection of Chlamydia trachomatis

With an estimated 3-4 million new cases per year, human infections from Chlamydia trachomatis are probably the most prevalent sexually transmitted disease (STD) in the United States. Diagnosis of Chlamydia is usually conducted by tissue culture methods. Direct immunofluorescence and ELISA tests have become available, but there remains a need for a test with better specificity and sensitivity. In response to this need, we have developed a rapid DNA hybridization assay using synthetic oligonucleotide probes to detect the presence of the Chlamydia trachomatis specific 7.4 kb plasmid. The assay involves solution phase hybridization of unlabelled probes, rapid capture of the probe-target duplex onto a microtitre dish surface, a new signal amplification technique that employs chemically cross-linked oligonucleotides, and an alkaline phosphatase labelled probe. Signal is obtained by reacting the labelled probe-target complex with an enzyme triggerable dioxetane substrate. Detection of the chemiluminescent output is performed either with a luminometer or by exposure to instant film. All 15 serovars of Chlamydia trachomatis react positively, while organisms known to co-inhabit the human urogenital tract react negatively.

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.

Prevalence of Chlamydia trachomatis infection in a population of asymptomatic women in a screening program for cervical cancer

The prevalence of Chlamydia trachomatis infection in a population of women with no symptoms of sexually transmitted disease was investigated. These women, aged 35-55 years, participated in a screening program for cervical cancer. With the use of a direct immunofluorescence method, 109 out of 2,470 smears tested were positive for Chlamydia trachomatis, indicating an overall prevalence of 4.4%. No changes in prevalence were found when five-year cohorts of this group were analyzed, indicating that age-dependent changes or epidemiological factors do not result in a different (decreased) prevalence over the ages 35 to 55 years. The prevalence of Trichomonas vaginalis and fungi, as detected by cytological screening, was lower than that observed for Chlamydia trachomatis: 3.1 and 2.1%, respectively. Of the 109 smears positive for Chlamydia trachomatis, 90 showed cervical cells with reactive changes (out of 1,490 smears with PAP II), whereas no cytological changes were found in 15 cases (out of 884 smears with PAP I). Changes suggestive of mild or moderate dysplasia were found in only four cases (out of 93 smears with PAP III). The results indicate that Chlamydia trachomatis is associated with reactive changes of endocervical cells and raise serious questions about whether prevention of possible secondary effects such as infertility and pelvic inflammatory disease can be achieved by a combined screening program for cervical cancer and Chlamydia trachomatis.

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.

Comparison of DNA-spot hybridization, cell culture and direct immunofluorescence staining for the diagnosis of avian chlamydiae

DNA-spot hybridization, cell culture and direct immunofluorescence staining were compared for the detection of avian Chlamydia psittaci strains in cell culture dilutions and in routine samples submitted for diagnosis. With dilutions of infected cell culture material, growth in BGM cells was by far the most sensitive technique, detecting 0.01 infected cells (20 elementary bodies) ml-1. DNA-spot hybridization and direct immunofluorescence staining were of approximately equal sensitivity, both detecting 16 infected cells (3.2 x 10(4) elementary bodies) per ml-1. When 27 avian liver and spleen samples were assayed, all 3 tests performed similarly (13 positive and 12 negative by all 3 tests). This suggests that in most avian samples presented for diagnosis, sufficient numbers of chlamydiae are present to allow any of the test to the be used. Thus, the direct immunofluorescence staining method is currently the test of choice for routine diagnosis since it is available in kit form, is relatively simple and quick to perform, and like DNA-spot hybridization, detects non-viable as well as viable organisms. However, if low levels of chlamydiae are to be effectively detected, such as in carrier birds or birds with recently acquired infections, then cell culture should be used.

Staining characteristics of six commercially available monoclonal immunofluorescence reagents for direct diagnosis of Chlamydia trachomatis infections

Using purified elementary bodies of 14 Chlamydia trachomatis serovars in an in vitro assay, we compared the staining characteristics of six commercially available monoclonal antibody reagents used for direct immunofluorescent staining of patient smears. Considerable variation in the degree of brightness, consistency of staining, and specificity of the six reagents was found. Monoclonal antibodies against the major outer membrane proteins of C. trachomatis produced brighter fluorescence, more consistent elementary body morphology, and less nonspecific staining than did monoclonal antibodies directed against chlamydial lipopolysaccharide.

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.

Multicenter comparative evaluation of two rapid microscopic methods and culture for detection of Chlamydia trachomatis in patient specimens

Four hundred and seventy-three men and women at high risk for sexually transmitted disease were tested for the presence of Chlamydia trachomatis in the urethra or the endocervix. Four groups were involved in this multicenter study of two direct fluorescent-antibody microscopy tests, Kallestad Pathfinder and Syva Microtrak, compared with culture techniques. Results from the test sites indicated that there was no significant difference overall in the sensitivity and specificity of the two test kits. However, there was some interlaboratory variation seen in the sensitivity of the microscopy, but little difference in the specificity. Either kit could be an effective screening method for C. trachomatis in high-risk populations.

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.