Role of confirmatory PCRs in determining performance of Chlamydia Amplicor PCR with endocervical specimens from women with a low prevalence of infection

A multiplexed microfluidic PCR assay for sensitive and specific point-of-care detection of Chlamydia trachomatis

BACKGROUND

Chlamydia trachomatis (Ct) is the most common cause of bacterial sexually transmitted diseases (STD) worldwide. While commercial nucleic acid amplification tests (NAAT) are available for Ct, none are rapid or inexpensive enough to be used at the point-of-care (POC). Towards the first Ct POC NAAT, we developed a microfluidic assay that simultaneously interrogates nine Ct loci in 20 minutes.

METHODOLOGY AND PRINCIPAL FINDINGS

Endocervical samples were selected from 263 women at high risk for Ct STDs (∼35% prevalence). A head-to-head comparison was performed with the Roche-Amplicor NAAT. 129 (49.0%) and 88 (33.5%) samples were positive by multiplex and Amplicor assays, respectively. Sequencing resolved 71 discrepant samples, confirming 53 of 53 positive multiplex samples and 12 of 18 positive Amplicor samples. The sensitivity and specificity were 91.5% and 100%, and 62.4% and 95.9%, respectively, for multiplex and Amplicor assays. Positive and negative predictive values were 100% and 91%, and 94.1% and 68.6%, respectively.

CONCLUSIONS

This is the first rapid multiplex approach to Ct detection, and the assay was also found to be superior to a commercial NAAT. In effect, nine simultaneous reactions significantly increased sensitivity and specificity. Our assay can potentially increase Ct detection in globally diverse clinical settings at the POC.

Immune pathogenesis of asymptomatic chlamydia trachomatis infections in the female genital tract

Chlamydia trachomatis (CT) infections of the female genital tract, although frequently asymptomatic, are a major cause of fallopian-tube occlusion and infertility. Early stage pregnancy loss may also be due to an unsuspected and undetected CT infection. In vitro and in vivo studies have demonstrated that this organism can persist in the female genital tract in a form undetectable by culture. The mechanism of tubal damage as well as the rejection of an embryo may involve an initial immune sensitization to the CT 60 kD heat shock protein (HSP), followed by a reactivation of HSP-sensitized lymphocytes in response to the human HSP and the subsequent release of inflammatory cytokines. The periodic induction of human HSP expression by various microorganisms or by noninfectious mechanisms in the fallopian tubes of women sensitized to the CT HSP may eventually result in tubal scarring and occlusion. Similarly, an immune response to human HSP expression during the early stages of pregnancy may interfere with the immune regulatory mechanisms required for the maintenance of a semiallogeneic embryo.

Comparison of an in-house PCR assay, direct fluorescence assay and the Roche AMPLICOR Chlamydia trachomatis kit for detection of C. trachomatis

To improve the control of Chlamydia trachomatis infection in India, a rapid, specific and cost-effective method is much needed. We developed an in-house PCR assay by targeting a unique genomic sequence encoding a protein from the C. trachomatis phospholipase D endonuclease superfamily that produces an amplified fragment of 368 bp. The specificity of the primers was confirmed using genomic DNA from other sexually transmitted disease-causing and related micro-organisms and from humans. The assay was highly sensitive and could detect as low as 10 fg C. trachomatis DNA. Clinical evaluation of the in-house-developed PCR was carried out using 450 endocervical specimens that were divided in two groups. In group I (n=274), in-house PCR was evaluated against the direct fluorescence assay. The resolved sensitivity of the in-house PCR method was 97.22 % compared with 88 % for the direct fluorescent antibody assay. In group II (n=176), the in-house PCR was compared with the commercial Roche AMPLICOR MWP CT detection kit. The resolved sensitivity of the in-house PCR assay reported here was 93.1 % and the specificity was 97.46 %, making it a cost-effective alternative for routine diagnosis of genital infection by C. trachomatis. The method should facilitate early detection leading to better prevention and treatment of genital infection in India.

Reasons for testing women for genital Chlamydia trachomatis infection in the Calgary region

OBJECTIVE

To determine the clinical reason(s) for screening women with varying degrees of risk for genital Chlamydia trachomatis (CT) in the Calgary region.

DESIGN

Women aged 15 to 75 years were enrolled at various patient care locations. Pertinent risk factors for genital CT infection were recorded and a gynecological examination was performed. Two endocervical swabs and a first-void urine sample were collected for CT detection using two different nucleic acid amplification test methods.

SETTING

Calgary is an urban region that provides healthcare services to a population of almost one million people. Microbiology services are provided by Calgary Laboratory Services through a centralized regional laboratory service.

MAIN RESULTS

504 women with a mean age of 28.1 +/-SD 8.22 years were enrolled. Two hundred ninety-one women (57.8%) were at high risk for acquiring genital CT infection. Twenty-eight (5.6%) tested positive for CT infection and almost all of these women (26 of 28, 93%) had risk factors for acquiring infection. Of the high-risk women, 9.8% were CT positive versus only 1.3% of women at low risk (P=0.0001). Only two of 152 (1.3%) women older than 30 years had genital CT infections. Although most women were asymptomatic, those with laboratory-confirmed CT infection were more likely to have genitourinary symptoms. Three hundred forty-three of 476 (72%) women who did not have genital CT infection had no risk factors, and screening was done as part of a routine gynecological examination for other purposes (prenatal visit, Pap smear).

CONCLUSION

Women without risk factors are being screened routinely for genital CT infection as part of a routine gynecological examination done for other reasons. Elimination of the routine screening of low-risk women older than 30 years of age would decrease the current regional utilization of CT tests by as much as one-third.

Diagnosis and assessment of trachoma

Trachoma is caused by Chlamydia trachomatis. Clinical grading with the WHO simplified system can be highly repeatable provided graders are adequately trained and standardized. At the community level, rapid assessments are useful for confirming the absence of trachoma but do not determine the magnitude of the problem in communities where trachoma is present. New rapid assessment protocols incorporating techniques for obtaining representative population samples (without census preparation) may give better estimates of the prevalence of clinical trachoma. Clinical findings do not necessarily indicate the presence or absence of C. trachomatis infection, particularly as disease prevalence falls. The prevalence of ocular C. trachomatis infection (at the community level) is important because it is infection that is targeted when antibiotics are distributed in trachoma control campaigns. Methods to estimate infection prevalence are required. While culture is a sensitive test for the presence of viable organisms and nucleic acid amplification tests are sensitive and specific tools for the presence of chlamydial nucleic acids, the commercial assays presently available are all too expensive, too complex, or too unreliable for use in national programs. There is an urgent need for a rapid, reliable test for C. trachomatis to assist in measuring progress towards the elimination of trachoma.

Improved sensitivity of the Chlamydia trachomatis Cobas Amplicor assay using an optimized procedure for preparation of specimens

The aim of this study was to evaluate the performance of an improved sample preparation procedure that enhances the sensitivity of the Chlamydia trachomatis Cobas Amplicor assay (Roche, Switzerland). This procedure was developed after it was observed that, in some cases, endocervical swabs positive for Chlamydia trachomatis in a direct immunofluorescence assay were negative in the Chlamydia trachomatis Cobas Amplicor. For this procedure, the initial sample volume was increased over that recommended by the manufacturer, the sample was concentrated by centrifugation, and the yield of the extraction was increased by an additional enzymatic lysis. Five hundred sixteen endocervical swabs from women visiting a family planning clinic were tested in parallel by the Chlamydia trachomatis Cobas Amplicor using the extraction procedure recommended by the manufacturer and the modified in-house sample preparation procedure. Eight samples were positive with both procedures. Seven additional samples were positive with the in-house method only. The results show that the in-house sample preparation procedure markedly improves the test sensitivity of the Chlamydia trachomatis Cobas Amplicor assay. Consequently, the use of this improved screening protocol will facilitate the detection of even low-level infections with Chlamydia trachomatis, which in turn will lead to the introduction of earlier therapeutic interventions.

Evaluation of sequential testing strategies using non-amplified and amplified methods for detection of Chlamydia trachomatis in endocervical and urine specimens from women

Nucleic acid amplification tests (NAAT) are more sensitive than other methods for the diagnosis of Chlamydia trachomatis (CT) genital infections. Two unique sequential testing strategies that employed two different commercial NAAT methods to detect CT in a population of women with widely varying infection risk were evaluated. Specimens from 504 women aged 15 to 75 years were studied. Two endocervical swabs and a urine sample were collected from each woman. One swab was initially tested using the Access enzyme immunoassay (EIA) (Beckman). An aliquot from the EIA extraction was subsequently amplified using the COBAS AMPLICOR CT assay (PCR) (Roche). The second swab was initially tested using the PACE 2 CT hybridization assay (Gen-Probe). An aliquot was pipetted off prior to performing the PACE 2 assay and also amplified using the AMP-CT assay (TMA) (Gen-Probe). Urine samples were tested for CT using both NAAT methods. True CT infections were defined as any woman that was confirmed to be positive on both NAAT results from endocervical swabs. The results of all other CT assays were compared against this expanded gold standard. 28 women were confirmed to have CT infection giving an overall prevalence of 5.6%; low-risk women had a rate of 1.3% while high-risk women had a rate of 9.8%. NAAT methods have a higher sensitivity for detecting CT cervicitis when swabs are tested compared to urine. The positive predictive value of NAAT is decreased when testing low risk women. Limited automation makes it difficult to test a high volume of samples (i.e., > 100 swabs and/or urines) using either of these NAAT methods and continue to provide same day results. Laboratories performing CT testing must define the female population served so that appropriate diagnostic strategies can be employed.

Screening for chlamydial infection

OBJECTIVES

To examine data on the effectiveness of screening for chlamydial infection by a physician or other health care professional. Specifically, we examine the evidence that early treatment of chlamydial infection improves health outcomes, as well as evidence of the effectiveness of screening strategies in nonpregnant women, pregnant women, and men, and the accuracy of tests used for screening. This review updates the literature since the last recommendation of the U.S. Preventive Services Task Force published in 1996.

SEARCH STRATEGY

We searched the topic of chlamydia in the MEDLINE, HealthSTAR, and Cochrane Library databases from January 1994 to July 2000, supplemented by reference lists of relevant articles and from experts in the field. Articles published prior to 1994 and research abstracts were cited if particularly important to the key questions or to the interpretation of included articles.

SELECTION CRITERIA

A single reader reviewed all English abstracts. Articles were selected for full review if they were about Chlamydia trachomatis genitourinary infections in nonpregnant women, pregnant women, or men and were relevant to key questions in the analytic framework. Investigators read the full-text version of the retrieved articles and applied additional eligibility criteria. For all topics, we excluded articles if they did not provide sufficient information to determine the methods for selecting subjects and for analyzing data.

DATA COLLECTION AND ANALYSIS

We systematically reviewed three types of studies about screening in nonpregnant women that relate to three key questions: (1) studies about the effectiveness of screening programs in reducing prevalence rates of infection, (2) studies about risk factors for chlamydial infection in women, and (3) studies about chlamydial screening tests in women. Our search found too few studies on pregnant women to systematically review, although pertinent studies are described. We systematically reviewed two types of studies about screening in men: (1) studies about prevalence rates and risk factors for chlamydial infection in men and (2) studies about chlamydial screening tests in men.

MAIN RESULTS

Nonpregnant women. The results of a randomized controlled trial conducted in a large health maintenance organization indicate that screening women selected by a set of risk factors reduces the incidence of pelvic inflammatory disease (PID) over a 1-year period. Changes in population prevalence rates have not been well documented because few studies have employed a representative population sample. Age continues to be the best predictor of chlamydial infection in women, with most studies evaluating cut-offs at age younger than 25 years. Other risk factors may be useful predictors, but these are likely to be population specific. To determine the accuracy of screening tests for women, we retrieved and critically reviewed 34 articles on test performance. Results indicate that endocervical swab specimens and first-void urine specimens have similar performance when using DNA amplification tests and have better sensitivity than endocervical culture. Recurrent chlamydial infections in women have been associated with increased risks for PID and ectopic pregnancies. Pregnant women. The Second Task Force recommendations for screening pregnant women were based on two major studies demonstrating improved pregnancy outcomes following treatment of chlamydial infection. We identified no recent studies on this topic in our literature search. Very few studies describe risk factors for chlamydial infection in pregnant women. Nonculture testing techniques appear to perform well in pregnant women, although studies are limited. Men. No studies described the effectiveness of screening or early treatment for men in reducing transmission to women or in preventing acute infections or complications in men. Studies of prevalence rates and risk factors for chlamydial infection in men are limited. Age lower than 25 years is the strongest known risk factor cited so far. Results of urethral swab specimens compared to first-void urine specimens were similar for DNA amplification tests. DNA amplification techniques are more sensitive than culture.

CONCLUSIONS

Screening women for Chlamydia trachomatis reduces the incidence of PID, and it is associated with reductions in prevalence of infection in uncontrolled studies. No studies were found to determine whether screening asymptomatic men would reduce transmission or prevent acute infections or complications. Age is the strongest risk factor for men and women. A variety of tests can detect chlamydial infection with acceptable sensitivity and specificity, including new DNA amplification tests that use either endocervical swabs in women, urethral swabs in men, or first-void urine specimens from men and women.

Detection of antimicrobial-treated Chlamydia trachomatis with Amplicor PCR test kit

A polymerase chain reaction (PCR) method for the detection of Chlamydia trachomatis has been developed and is now available in the clinical setting. However, one of the major problems with this method is possible false-positive detection posttreatment. Nonviable C. trachomatis was established by in-vitro exposure to an antimicrobial agent, and we tried to detect the nonviable cells (NVCs) of C. trachomatis by PCR with variant primer sets. C. trachomatis strains (D/UW-3/Cx) were cultured in a medium containing the antimicrobial agent, at 8 x MIC (minimal inhibitory concentration) 15 to 20 h postinfection. Amplicor and two sets of PCR primers were used to detect the DNA of NVCs. Serial passages of NVCs were done five times. All samples were positive on Amplicor, and all except the fourth passage were positive for the two sets of primers. Although the PCR test appears to be valuable, NVCs may possibly be detected by this method, and this may be clinically responsible for the false detection of C. trachomatis after appropriate antimicrobial chemotherapy.

Pooling cervical swabs and testing by ligase chain reaction are accurate and cost-saving strategies for diagnosis of Chlamydia trachomatis

Specimen pooling to achieve efficiency when testing urine specimens for Chlamydia trachomatis nucleic acids has been suggested. We pooled endocervical swabs from 1,288 women and also tested individual swabs by ligase chain reaction (LCR). Out of 53 positive specimens, pools of 4 or 8 specimens missed two positives, providing 96.2% accuracy compared to individual test results. Dilution and positive-control spiking experiments showed that negative specimens with inhibitors of LCR in the pool reduced the signal. Conversely, two extra positives, detected only through pooling, were negative by individual testing but became positive after storage, suggesting that fresh positive specimens with labile inhibitors may be positive in a pool because of dilution of inhibitors. For this population of women with a 4% prevalence of C. trachomatis infection, substantial savings in cost of reagents (55 to 63%) and technologist time (50 to 63%) made pooling strategies a desirable alternative to individual testing.

Inhibition of PCR in genital and urine specimens submitted for Chlamydia trachomatis testing

We determined the frequency of PCR inhibition in genital and urine specimens submitted for Chlamydia trachomatis testing using the internal control DNA provided with the COBAS AMPLICOR C. trachomatis test and assessed methods to remove it. Inhibition occurred in 65 of 906 (7%) cervical swabs, 23 of 51 (45%) urethral swabs, and 2 of 175 (1.1%) urine samples. Overall, inhibition was eliminated in processed specimens after storage at 4 degrees C in 77 of 90 specimens (86%), freezing at -70 degrees C in 59 of 82 specimens (72%), storage at 4 degrees C followed by either 1:100 dilution in 37 of 43 specimens (86%) or 1:10 dilution in 42 of 47 specimens (89%), and phenol-chloroform extraction in 79 of 80 specimens (99%). No positive specimens were missed due to inhibition. We conclude that PCR inhibition is rare with urine specimens and infrequent with endocervical swabs but occurs frequently with urethral swabs. The frequency of PCR inhibition may be significantly reduced by methods which can be easily incorporated into the processing of specimens.

Evaluation of bias in diagnostic-test sensitivity and specificity estimates computed by discrepant analysis

When a new diagnostic test is potentially more sensitive than the reference test used to classify persons as infected or uninfected, a substantial number of specimens from infected persons may be reference-test negative but new-test positive. Discrepant analysis involves the performance of one or more additional tests with these specimens, reclassification as infected those persons for whom the new-test-positive results are confirmed, and recalculation of the estimates of new-test sensitivity and specificity by using the revised classification. This approach has been criticized because of the bias introduced by the selective use of confirmation testing. Under conditions appropriate for evaluating a nucleic acid amplification (NAA) test for Chlamydia trachomatis infection with cell culture as the reference test, we compared the bias in estimates based on the discrepant-analysis classification of persons as infected or uninfected with that in estimates based on the culture classification. We concluded that the bias in estimates of NAA-test specificity based on discrepant analysis is small and generally less than that in estimates based on culture. However, the accuracy of discrepant-analysis-based estimates of NAA-test sensitivity depends critically on whether culture specificity is equal to or is slightly less than 100%, and it is affected by competing biases that are not fully taken into account by discrepant analysis.

Screening women for chlamydia trachomatis in family planning clinics: the cost-effectiveness of DNA amplification assays

BACKGROUND

Highly sensitive and specific DNA amplification assays are available for use on cervical and urine specimens. These new tests have the potential to identify more chlamydial infections than the commonly used enzyme immunoassay and DNA probe tests, yet they are more expensive. This study sought to assess the cost effectiveness of cell culture, enzyme immunoassay (EIA), DNA probe (Pace 2), polymerase chain reaction (PCR) of cervical and urine specimens, and ligase chain reaction (LCR) of cervical and urine specimens as screening tools for Chlamydia trachomatis in asymptomatic women younger than 30 years of age attending family planning clinics.

STUDY DESIGN

Program costs; medical cost savings of prevented sequelae in women, male sex partners, and infant; and number of prevented cases of pelvic inflammatory disease (PID), neonatal infections, and male sex partner urethritis and epididymitis were modeled in a decision analysis conducted from a health care system perspective. Results are expressed for a cohort of 18,000 women.

RESULTS

If no screening for C. trachomatis were conducted in Maryland, 497 cases of PID would develop, costing $2.2 million in future medical costs. Use of EIA to detect chlamydial infection would prevent 240 cases of PID and save $887,000 over no screening. Alternatively, use of DNA amplification assays on urine specimens would prevent up to an additional 66 cases and save $287,100 over EIA. Use of LCR on cervical specimens would prevent at least 13 additional cases of PID over the urine-based assays, but would cost $3,005 for each additional case prevented. In women receiving routine pelvic examinations, LCR of cervical specimens would prevent the most disease and provide the highest cost savings. In women not receiving routine pelvic examinations, use of LCR on cervical specimens would prevent the most disease but would cost approximately $28,000 per additional case of PID prevented over DNA amplification of urine.

CONCLUSIONS

Compared with EIA screening, the strategy with the lowest program costs, a screening strategy that combines use of DNA amplification on cervical specimens in women receiving pelvic examinations, and DNA amplification of urine in women with no medical indications necessitating a pelvic examination, prevents the most cases of PID and provides the highest cost savings. With enhanced sensitivity over the other diagnostic assays and with the use of noninvasive specimen collection, DNA amplification assays should be implemented as cost-effective components of a screening program for C. trachomatis.

Detection of Chlamydia trachomatis in urine samples by nucleic acid tests: comparison with culture and enzyme immunoassay of genital swab specimens

Two commercially available nucleic acid-based tests, ligase chain reaction (LCR; Abbott Laboratories) and PCR (Roche Diagnostics), for the detection of Chlamydia trachomatis in male and female urine samples were compared with culture and enzyme immunoassay (EIA) (Microtrak; Syva) for C. trachomatis detection in genital samples. The samples were collected from 1,005 patients who attended a sexually transmitted disease clinic. In this study population, the prevalence of the infection was 4%. Specimens which were reactive in any of the tests were retested with a different PCR test using primers directed against the major outer membrane protein gene. With a "gold standard" of a positive culture, or any other positive test result if it was confirmed by an independent test, the Roche PCR (95% sensitive, 99.9% specific) was more sensitive than the LCR (75% sensitive, 100% specific) (chi2, P < 0.0001) while both tests were more sensitive than culture (58% sensitive, 100% specific) or EIA (45% sensitive, 100% specific) (chi2, P < 0.001). The Roche PCR and Abbott LCR tests of urine identified 65% and 30% more positive patients, respectively, than did testing by culture of urethral or cervical specimens. Nucleic acid testing of urine specimens for C. trachomatis is a more sensitive and convenient method for the detection of genital infection.

Use of a single swab in multi-microbe or flex trans transport medium for detection of Chlamydia trachomatis by Roche Amplicor PCR and culture in specimens from two different patient populations

The Roche Amplicor PCR increased the detection of Chlamydia trachomatis compared with culture in promptly processed clinical specimens from a local clinic (100 and 86.5%, respectively) and in samples with delayed processing transported from distant facilities (100 and 72.7%, respectively). A single swab collected in culture transport medium was used. Two media, Multi-Microbe and Flex Trans, were tested and found to be equally acceptable.

Lowering the cut off value of an automated chlamydia enzyme immunoassay and confirmation by PCR and direct immunofluorescent antibody test

AIMS

To increase the sensitivity of an automated chlamydia enzyme immunoassay by significantly lowering its cut off value, and to maintain specificity by confirmation with polymerase chain reaction (PCR) and direct immunofluorescent antibody test (DFA).

METHODS

Over five months, the cut off value of the enzyme immunoassay used to screen urogenital samples for chlamydia antigen was reduced from 80 to 10. Samples with a test value of 10 or above were further tested with a commercial PCR assay. All samples during the first three months and discrepant samples during the last two months of the study were also tested with the DFA.

RESULTS

3250 urogenital swabs (1246 urethral, 1335 endocervical, 669 pooled urethral/endocervical) from 1246 males and 2004 females were processed. Using the manufacturer's recommended cut off of 80, the enzyme immunoassay identified chlamydia antigen in 134 samples (4.1%). Using the lower cut off value of 10 and either PCR or DFA as the confirmatory test, Chlamydia trachomatis was identified in 178 samples (5.5%). Thus, 45 additional positive samples were identified and the confirmed detection rate was increased by 33.8% (45/133). Excluding equivocal PCR results, the concordance between DFA and PCR was 91.8%. This strategy increased the detection rate by 2.1% in men and 0.9% in women (significant only in men). In female patients, pooled urethral/endocervical swabs as a specimen gave a significantly higher yield than endocervical swabs regardless of whether the lower cut off strategy was used.

CONCLUSIONS

This strategy of significantly lowering the cut off test value with confirmation on the same specimen by either PCR or DFA is feasible and cost effective. The use of pooled urethral/ endocervical specimens in females should be considered routinely as detection rate was significantly improved.

Current methods of laboratory diagnosis of Chlamydia trachomatis infections

Infections caused by Chlamydia trachomatis are probably the most common sexually transmitted diseases in the United States. Commonly unrecognized and often inadequately treated, chlamydial infections can ascend the reproductive tract and cause pelvic inflammatory disease, which often results in the devastating consequences of infertility, ectopic pregnancy, or chronic pelvic pain. C. trachomatis infections are also known to increase the risk for human immunodeficiency virus infection. The obligate intracellular life cycle of C. trachomatis has traditionally required laboratory diagnostic tests that are technically demanding, labor-intensive, expensive, and difficult to access. In spite of these historical challenges, however, laboratory diagnosis of C. trachomatis has been a rapidly advancing area in which there is presently a wide array of commercial diagnostic technologies, costs, manufacturers. This review describes and compares the diagnostic methods for C. trachomatis infection that are currently approved for use in the United States, including the newest DNA amplification technologies which are yet to be licensed for commercial use. Issues to consider in selecting a test for purposes of screening versus diagnosis based on prevalence, performance, legal, social, and cost issues are also discussed.

Detection of PCR inhibitors in cervical specimens by using the AMPLICOR Chlamydia trachomatis assay

To determine that susceptibility of AMPLICOR Chlamydia trachomatis PCR to inhibitory factors possibly present in cervical specimens, we obtained cervical specimens from 200 gynecology patients attending our outpatient clinic. The prevalence of C. trachomatis infection was 4.1%, as determined by cell culture. All AMPLICOR specimens were tested in one procedure as described by the manufacturer, and after the specimen was spiked with C. trachomatis, several other pretreatment protocols were used. Complete inhibition of the PCR was observed in 38 (19%) cervical specimens. Heat treatment at 95 degrees C, freeze-thawing, or 10-fold dilution of the samples reduced the initial inhibition to 9, 16, or 9%, respectively. A combination of heat treatment and 10-fold dilution reduced the inhibition to 4% of the samples. A second specimen type (swabs inoculated in 0.2 M sucrose phosphate buffer [2SP]) was also evaluated. A 10-fold dilution of the spiked 2SP specimen resulted in an inhibition rate of 6%, which was comparable to that obtained by centrifugation of the 2SP specimen prior to processing. Furthermore, it was shown that the inhibition was not correlated with blood contamination. Processing the specimens on the day of collection or the day after resulted in a higher inhibition rate than did delayed processing (27.6 versus 15.5%, respectively). An inverse correlation was found between the concentration of C. trachomatis added to the sample and the rate of inhibition observed. The inhibition was partly correlated with the pH of the cervical mucosa. Decreased inhibition was found at pH values of > or = 7.5. The effects of blood, pH, and delay in processing were all evaluated by using the AMPLICOR specimen. We conclude that the susceptibility of AMPLICOR C. trachomatis PCR to inhibiting factors in cervical specimens can be significantly reduced if the pretreatment procedure includes heat treatment or the use of 2SP transport medium. Also, a 10-fold dilution of the clinical specimen followed by heat treatment will largely prevent the inhibition of this PCR.

Confirmation of the Syva MicroTrak enzyme immunoassay for chlamydia trachomatis by Syva Direct Fluorescent Antibody Test

BACKGROUND AND OBJECTIVES

The Syva Micro Trak enzyme immunoassay (EIA) is used widely for screening women infected with Chlamydia trachomatis. Confirmatory tests used in conjunction with EIA screening have shown that false-positive results are common.

GOALS

To evaluate the specificity of the Syva MicroTrak EIA by confirmation of positive specimens with the Syva Direct Fluorescent Specimen Test.

STUDY DESIGN

Of 6,039 endocervical specimens collected from women attending Colorado family planning clinics, 328 positive EIA results (5.4%) were obtained by Syva MicroTrak EIA. A random subset of 136 positive specimens was tested by Syva Direct Specimen Test. Twenty of 136 specimens (14.7%) negative by Syva Direct Specimen testing were also tested by Syva blocking antibody tests (9 of 20 positive, 45%) and Roche Amplicor polymerase chain reaction (PCR; 6 of 20 positive, 30%). Of 20 specimens positive by Syva MicroTrak EIA and negative by Syva Direct Specimen Test, 11 (55%) were also negative by blocking antibody and PCR, including three specimens with initial EIA sample-to-cutoff ratios greater than 2.

CONCLUSIONS

Confirmatory testing of Syva MicroTrak EIA positive specimens with Syva Direct Specimen Test showed that 14.7% were false positive. Coupling the Syva Direct Specimen test with either blocking antibody or PCR reduces the rate of false-positive results to 8%.

Evaluation of automated COBAS AMPLICOR PCR system for detection of several infectious agents and its impact on laboratory management

We evaluated the COBAS AMPLICOR (CA) PCR system (Roche Diagnostic Systems) designed for automated PCR amplification and detection of nucleic acids from infectious agents in clinical samples. The Roche AMPLICOR microwell plate (MWP) PCR was the reference method. CA amplifies target nucleic acid, captures the biotinylated amplification products by using magnetic particles coated with specific oligonucleotide probes, and detects the bound products colorimetrically. For Mycobacterium tuberculosis, the correlation of the results of CA tests with those of MWP tests was 100% with 230 samples, including 20 culture-positive samples. For hepatitis C virus, the correlation was 100% with 214 samples, including 60 positive samples. MultiPlex CA analysis of 199 cervical specimens for Chlamydia trachomatis, Neisseria gonorrhoeae, and the internal control gave 100% concordance. These samples included 19 C. trachomatis and 3 N. gonorrhoeae culture-positive samples. Overall, the agreement between PCR methods for all 842 comparisons was 100%. Compared with culture, the sensitivities of the assays for C. trachomatis and M tuberculosis were > or = 95%. After spiking alternating amplification tubes in the CA system with 10(14) copies of the Chlamydia amplicon per ml, we were unable to demonstrate any carryover cross-contamination of negative samples. Using the criteria of the College of American Pathologists workload recording method, we found that the total hands-on time to produce CA PCR results was 4.4, 7.9, and 3.3 min for M. tuberculosis, hepatis C virus, and the MultiPlexed assay for chlamydia plus gonorrhea and an internal control, respectively. The CA system brings true PCR automation to laboratories. In addition to the accuracy of automated results, the CA system provides labor savings, provides containment of the amplification and detection components of PCR, and supports both MultiPlex amplification and sequential algorithm (ReFlex) detection of analytes.

The role of nucleic acid amplification and detection in the clinical microbiology laboratory

Clinical microbiology is in the midst of a new era. Methodology that is based on nucleic acid detection has slowly appeared in the diagnostic laboratory, and is revolutionizing our ability to assist physicians in the diagnosis and management of patients suffering from infectious diseases. Much like the introduction of immunoassays built around hybridoma technology in the 1980s, considerable doubt and promise exist hand in hand in the 1990s. Conventional testing that is technically straight forward, informative, and timely will always be a part of clinical microbiology; however, considerable room for improvement exists with organisms/diseases for which laboratory methods are limited. Nucleic acid methodology will have its greatest and long-awaited impact in this arena.

Diagnosis of Chlamydia trachomatis infections in asymptomatic men and women by PCR assay

A PCR assay was evaluated for its ability to detect genital chlamydial infection in asymptomatic men and women. Urethral swab specimens were collected from 472 men for culture and PCR assay, and first-void urine (FVU) specimens were collected from 379 of these men for enzyme immunoassay (EIA) and PCR assay. Cervical swab specimens were collected from 242 women for culture, EIA, and PCR assay. Patients were considered infected if they were culture positive or positive by PCR with both plasmid- and major outer membrane protein-based primers. By using this extended "gold standard," the prevalence of infection in this population was 7.6% for men and 7.9% for women. For men, the sensitivities of urethral swab specimen culture and PCR and FVU specimen EIA and PCR were 61, 72, 55, and 91%, respectively. All assays had specificities of > or = 99.8%. The positive and negative predictive values for PCR testing of FVU specimens were 100 and 99.4%, respectively, compared with values of 96.3 and 97.8%, respectively, for PCR of urethral swab specimens. The sensitivities of cervical swab specimen culture and PCR testing were 42 and 90%, respectively, with corresponding specificities of 100 and 99.3%. All cervical swabs were negative by EIA. Molecular techniques such as PCR assays are valuable tools for the detection of symptomatic genital chlamydial infection. In particular, PCR assays of FVU specimens from men offer a highly sensitive, noninvasive screening tool that will likely improve patient compliance for diagnostic testing.

Periodic health examination, 1996 update: 2. Screening for chlamydial infections. Canadian Task Force on the Periodic Health Examination

OBJECTIVE

To update the 1984 recommendations of the Canadian Task Force on the Periodic Health Examination on the routine screening of asymptomatic patients for infection with Chlamydia trachomatis.

OPTIONS

Screening, with the use of culture or nonculture tests, of the general population, of certain high-risk groups or of all pregnant women; or no routine screening.

OUTCOMES

Rates of asymptomatic and symptomatic chlamydial infection, perinatal complications, longterm complications of infection (i.e., pelvic inflammatory disease, infertility and ectopic pregnancy), coinfection with other sexually transmitted diseases, disease spread, hospital care, complications of therapy and costs of infection and of screening.

EVIDENCE

Search of MEDLINE for articles published between Jan. 1, 1983, and Dec. 31, 1995, with the use of the major MeSH heading "chlamydial infections," references from recent review articles and recommendation by other organizations.

VALUES

The evidence-based methods of the Canadian Task Force on the Periodic Health Examination were used. Advice from reviewers and experts and recommendations of other organizations were taken into consideration. Prevention of symptomatic disease and decreased overall costs were given high values.

BENEFITS, HARMS AND COSTS

The greatest potential benefits of screening asymptomatic patients for chlamydial infections are the prevention of complications, especially infertility and perinatal complications, and the prevention of disease spread. There is no evidence that screening of the general population for chlamydial infections leads to a reduction in complications, and screening may increase costs. However, there is evidence that annual screening of selected high-risk groups and of pregnant women during the first trimester is beneficial in preventing symptoms and reducing the overall cost resulting from infection.

RECOMMENDATIONS

There is fair evidence to support screening and treatment of pregnant women during the first trimester (grade B recommendation) as well as annual screening and treatment of high-risk groups (sexually active women less than 25 years of age, men or women with new or multiple sexual partners during the preceding year, women who use nonbarrier contraceptive methods and women who have symptoms of chlamydial infection: cervical friability, mucopurulent cervical discharge or intermenstrual bleeding; grade B recommendation). There is fair evidence to exclude routine screening of the general population (grade D recommendation).

VALIDATION

These recommendations are similar to those of the US Preventive Services Task Force and the US Centers for Disease Control and Prevention, Atlanta.

SPONSOR

These guidelines were developed and endorsed by the Canadian Task Force on the Periodic Health Examination, which is funded by Health Canada and the National Health Canada and the National Health Research and Development Program. The principal author (H.D.D.) was supported in part by the Ontario Ministry of Health and the Canadian Infectious Diseases Society Lilly Fellowship.

Detection of Chlamydia trachomatis by a ligase chain reaction amplification method

BACKGROUND AND OBJECTIVES

The ligase chain reaction is an in vitro DNA amplification technique that exponentially amplifies selected DNA sequences.

GOAL

To evaluate a ligase chain reaction assay for the detection of Chlamydia trachomatis cryptic plasmid DNA (LCx Chlamydia) in patients routinely attending a sexually transmitted disease center in Italy.

STUDY DESIGN

Urethral or cervical swabs were obtained from 501 consecutive patients (334 men and 167 women). The samples were assayed in parallel with LCx Chlamydia and conventional tissue culture; discordant results were further assayed by direct immunofluorescence and a ligase chain reaction with alternate primers.

RESULTS

After resolution of discordant results, the LCx method showed a sensitivity, specificity, positive predictive value, and negative predictive value of 100%, 99.3%, 96.7%, and 100% in men; 100%, 100%, 100%, and 100% in women; and 100%, 99.5%, 97.1%, and 100% overall, respectively. By comparison, the sensitivity of tissue culture was 81.4% in men, 50% in women, and 77.6% overall.

CONCLUSIONS

The automated LCx method is sensitive, fast, and accurate and represents a useful diagnostic tool for C. trachomatis infection, even in low and medium prevalence populations.

Genital chlamydial infection among women in Nicaragua: validity of direct fluorescent antibody testing, prevalence, risk factors and clinical manifestations

OBJECTIVE

To validate the performance of a direct fluorescence antibody (DFA) test and to determine the prevalence, risk factors and clinical manifestations of cervical chlamydia infection in different groups of women in Nicaragua.

STUDY POPULATION

926 women, 863 routine clinic attenders (mean age 27 years) and 63 sex workers (mean age 25 years) attending health centres in León, Corinto, Matagalpa and Bluefields.

METHODS

Cervical specimens were examined using the Syva MicroTrak test system with a cut-off of 10 or more elementary bodies (EBs). The DFA results were validated by a one-step polymerase chain reaction (PCR) assay. Discordant results were further examined in nested PCR assays directed at two different target genes. An interviewer-administered questionnaire and a standard gynaecological examination were completed.

RESULTS

Sensitivity of DFA was 80.1%, specificity 98.3%, and positive and negative predictive values 62.5% and 99.3%, respectively. Values were lower in locations where samples thawed because of electricity breaks and higher among sex workers. The majority of discordant results was confirmed as positive in nested PCR assays. Prevalence of cervical chlamydia infection based on positivity in DFA and/or PCR ranged from 2% among routine clinic attenders aged 35 years or older, to 8% among adolescent clinic attenders, and to 14% among sex workers. Among routine clinic attenders, young age (odds ratio [OR] 3.6, 95% confidence intervals [95% CI] 1.4-8.9 for women aged 15-19 years as compared with 1 in women 25 years of age or older) and use of oral contraceptives (OR 4.0, 95% CI 1.7-9.6) were the only statistically significant risk factors identified in multivariate logistic regression analysis. Presence of mucopurulent cervical discharge (OR 5.9, 95% CI 3.0-11.5) and presence of ectropion (OR 2.6, 95% CI 1.1-6.5) were the clinical signs independently associated with infection.

CONCLUSIONS

Our results indicate that the DFA test was sensitive and specific while the performance of the PCR assay depends on adequate storage of samples. Genital C trachomatis infection is a common health problem among women in Nicaragua. The wide implementation of syndromic STD management algorithms together with health education programmes aimed at young people is the most promising approach to control STD in Nicaragua.

PCR and direct fluorescent-antibody staining confirm Chlamydia trachomatis antigens in swabs and urine below the detection threshold of Chlamydiazyme enzyme immunoassay

In order to test the hypothesis that specimens blocking with a neutralizing reagent below the cutoff of the Chlamydiazyme enzyme immunoassay represent infected patients, we used direct fluorescent-antibody staining for elementary bodies (EBs) and PCR to confirm results for cervical swabs collected from 55,963 women and urethral swabs or first-void urine (FVU) samples collected from 5,781 men attending physicians' offices in the Toronto, Canada, area. Within a grey zone arbitrarily selected to represent values up to 40% below the positive threshold of the test run, 134 cervical swabs, 44 urethral swabs, and 39 FVU specimens exhibited a blocking response ( > 50% reduction in signal). Three or more EBs were observed in each of 98 cervical swabs (73.1%), 38 urethral swabs (86.4%), and 21 FVU specimens (53.8%). Of the 36 cervical swabs with fewer than three EBs, 33 were PCR positive; the positive PCR results for male specimens were 6 of 6 urethral swabs and 17 of 18 FVU samples. Application of the blocking test to specimens negative in the Chlamydiazyme enzyme immunoassay but having optical densities within 40% of the cutoff added 14.2% (217 of 1,531 specimens) more positive results to the survey. A total of 213 of 217 samples (98.2%) were reconfirmed as having EBs or DNA.

Multiplex PCR for detection of Chlamydia trachomatis and Neisseria gonorrhoeae in Genitourinary specimens

We developed a multiplex PCR (M-PCR) assay for the simultaneous detection of Chlamydia trachomatis and Neisseria gonorrhoeae. M-PCR employed C. trachomatis-specific primers KL1-KL2 and N. gonorrhoeae-specific primers HO1-HO3 and produced products of 241 and 390 bp, respectively. PCR products were easily detected by agarose gel electrophoresis and confirmed by Southern hybridization using labelled oligonucleotide probes. M-PCR had a sensitivity of 10 fg of C. trachomatis and N. gonorrhoeae DNA (equivalent to 1 to 2 genome copies). M-PCR detected the presence of C. trachomatis and N. gonorrhoeae DNA in 15 male urethral and 12 female endocervical specimens, 3 of which were positive for C. trachomatis, 18 of which were positive for N. gonorrhoeae and 6 of which were positive for both organisms. M-PCR was evaluated further by testing 200 male first void urine (FVU) specimens, of which 18 were positive by C. trachomatis PCR and Chlamydiazyme and 4 were positive by C. trachomatis PCR but negative by Chlamydiazyme. All 22 FVU specimens were positive by a confirmatory PCR using a second plasmid target and were positive by M-PCR. Ten of 11 men with cultures that were positive for N. gonorrhoeae had FVU specimens that were positive by both N. gonorrhoeae PCR and M-PCR. Two other men with negative N. gonorrhoeae urethral cultures had FVU specimens that were positive by N. gonorrhoeae PCR, by two confirmatory N. gonorrhoeae PCR assays using 165 rRNA and cytosine methyltransferase primers, and by M-PCR. The sensitivity of M-PCR for detecting C. trachomatis was 100% (22 of 22 specimens), compared with 81.8% (18 of 22 specimens) for enzyme immunoassay. Sensitivity of M-PCR for N. gonorrhoeae was 92.3% (12 of 13 specimens) compared with 84.6% (11 of 13 specimens) for urethral culture. The specificity of M-PCR was 100% for both C. trachomatis (178 of 13 specimens) and N. gonorrhoeae (187 of 187 specimens). M-PCR testing of FVU specimens provided a sensitive and noninvasive method for detecting C. trachomatis and N. gonorrhoeae infection in men.

Improved PCR detection of Chlamydia trachomatis by using an altered method of specimen transport and high-quality endocervical specimens

Duplicate endocervical swabs were collected for detection of Chlamydia trachomatis by PCR (Roche Diagnostics). One swab was swirled in Specimen Transport Medium (Roche) for PCR testing and discarded. A saline aliquot from the other specimen, sent as a dry swab to the laboratory, was Papanicolaou stained to determine specimen adequacy, and the remainder was PCR tested. Significantly more (24%) PCR-positive results (118 versus 95; P < 0.001) were obtained with the dry specimens than with the swirled specimens when first tested. In addition, PCR-positive results were obtained with 107 (10.6%) of 1,007 microscopically adequate specimens but with only 3 (0.9%) of 341 inadequate specimens (P < 0.001).