Detection of Chlamydia trachomatis infection in urine samples from men and women by ligase chain reaction

Should asymptomatic men be included in chlamydia screening programs? Cost-effectiveness of chlamydia screening among male and female entrants to a national job training program

OBJECTIVE

To compare the cost-effectiveness of various chlamydia screening strategies within a population of male and female youth entering a national job training program.

STUDY DESIGN

Cost-effectiveness analysis of various chlamydia screening strategies among a cohort of 4000 female and male New England job training students. Strategies for women include (a) no screening, (b) universal endocervical DNA probe screening, (c) universal urine based NAAT screening, and (d) universal endocervical NAAT screening. Strategies for men include (a) no screening, (b) selective urine NAAT screening of leukocyte esterase (LE)-positive urines, and (c) universal urine-based NAAT screening.

RESULTS

Universal endocervical NAAT screening of women and universal urine NAAT screening of men were the most effective and cost-effective strategies individually and in combination. Endocervical NAAT screening of women prevented 23 more cases of PID and saved $27,000 more than endocervical DNA probe screening. Likewise, universal urine NAAT screening of men prevented 21 more cases of PID in their female partners and saved $16,000 more than selective urine NAAT screening of LE positive men.

CONCLUSIONS

Use of a sensitive NAAT to screen both men and women for chlamydia upon entry to a National Job Training Program is cost-effective, cost-saving, and provides a public health opportunity to substantially reduce chlamydia infections among youth at risk for sexually transmitted diseases.

Evaluation of Nucleic Acid Amplification Tests in the Absence of a Perfect Gold-Standard Test

During the past 10 years, medical diagnostic testing for sexually transmitted infections (STIs) has changed markedly as a result of the rapid expansion and marketing of nucleic acid amplification tests (NAATs). Among such new DNA/RNA-amplification techniques are the polymerase chain reaction (PCR), the ligase chain reaction (LCR), and the transcription-mediated amplification (TMA) tests. Regrettably, the test evaluation process undergone by these tests has not always been rigorous or scientifically sound. Here, we review the controversy surrounding the statistical evaluation of these NAATs. We also review some of the traditional and recent statistical methods developed to estimate test sensitivity and specificity parameters in the absence of reliable gold-standard tests. In particular, we review the traditional latent class modeling approach that requires the assumption of independence between diagnostic tests conditional on the true disease status, and the more recent procedures that relax the conditional independence assumption. Finally, we apply some of these statistical modeling techniques to real data to estimate the sensitivity and specificity of a NAAT for Chlamydia trachomatis. On the basis of the latent class modeling approach with a pessimistic prior for culture sensitivity, the NAAT specificity estimate was 97.6% and, on the basis of an optimistic prior, the specificity was 95.3%. Similarly, the sensitivity estimates ranged from 88.1% to 89.6%.

Comparison of strand displacement and ligase chain amplification for detection of Chlamydia trachomatis infection in urogenital specimens

Two amplification tests for the diagnosis of Chlamydia trachomatis infection, namely the ligase chain reaction (LCx) and the strand displacement assay (ProbeTec), were compared using samples from 1183 patients at sexually transmitted disease clinics. The overall prevalence of positive results was 8.0%, with agreement between the two assays of 98.8%. For endocervical, urethral and male urine samples, agreement was 99.3%, 99.4% and 97.7%, respectively. For ten discrepant samples, alternative amplification assays suggested that the LCx and ProbeTec assays gave erroneous results in six and four cases, respectively. Inhibition of amplification was observed with three (0.25%) urine specimens.

Limitations of screening tests for the detection of Chlamydia trachomatis in asymptomatic adolescent and young adult women

OBJECTIVE

The purpose of this study was to examine the performance of different test types, specimen sources, and collection methods for screening of genital Chlamydia trachomatis infection in young women.

STUDY DESIGN

Asymptomatic women aged 16 to 25 years collected their own vaginal swabs and a first-voided urine specimen; a clinician collected urethral, vaginal, and endocervical swabs for culture and nucleic acid amplification tests, polymerase chain reaction and ligase chain reaction. A positive culture, 2 positive nucleic acid amplification tests, or 1 positive nucleic acid amplification test confirmed by a separate nested polymerase chain reaction comprised the criterion standard to define a C. trachomatis-infected woman.

RESULTS

The prevalence of C. trachomatis was 22% (30/139 women). All 9 test results were available for 126 participants (91%). Sensitivities were comparable for polymerase chain reaction and ligase chain reaction (52%-63%), except for urine polymerase chain reaction (44%), and were lower for culture (22%-37%); specificities were 99% to 100%, except for urine ligase chain reaction (91%). Positive predictive values were >93%, except for urine ligase chain reaction (65%); negative predictive values were 83% to 91%. Combining nucleic acid amplification test results from 2 different specimens improved sensitivities without compromising specificity.

CONCLUSION

When C. trachomatis infection was defined by multiple tests from different specimen sources, the sensitivity of any 1 test from a single specimen source was lower than generally reported. The limitations of the use of a single test to identify C. trachomatis infection should be considered when test type, specimen source, and collection method for screening young women is being determined.

Cost-Effectiveness Analysis of Screening Adolescent Males for Chlamydia On Admission to Detention

BACKGROUND

Chlamydia trachomatis infections can lead to serious and costly sequelae. Because chlamydia is most often asymptomatic, many infected youth do not seek testing. Entry to a detention system provides an opportunity to screen and treat many at-risk youth. GOAL The goal of this study was to determine the cost-effectiveness of screening male youth for chlamydia on entry to detention.

STUDY DESIGN

Incremental cost-effectiveness of 3 chlamydia screening strategies was compared for a hypothetical cohort of 4000 male youth per year: 1) universal chlamydia screening using a urine-based nucleic acid amplification test (NAAT), 2) selective NAAT screening of urine leukocyte esterase (LE)-positive urines, and 3) no screening. The model incorporated programmatic costs of screening and treatment and medical cost savings from sequelae prevented in infected males and female partners. The analysis was conducted from the healthcare system perspective.

RESULTS

Chlamydia prevalence in the sampled population of 594 was 4.8%, and the average number of female sexual partners/infected male was 1.6. Universal NAAT screening was the most cost-effective strategy, preventing 37 more cases of pelvic inflammatory disease (PID) and 3 more cases of epididymitis than selective screening and saving an additional 24,000 dollars. The analysis was sensitive to NAAT cost, LE sensitivity, rate of PID development, PID sequelae cost, and number of female partners. Universal screening remained the most cost saving for prevalence as low as 2.8% or higher.

CONCLUSIONS

Universal chlamydia screening of adolescent males on entry to detention was the most cost-effective strategy. Savings are primarily the result of the prevention of PID in recent and future partners of index males. Screening detained male youth using a urine-based NAAT provides a public health opportunity to significantly reduce chlamydia infections in youth at risk for sexually transmitted diseases.

Sustained high prevalence of Chlamydia trachomatis infections in female army recruits

BACKGROUND

Chlamydia trachomatis infections are prevalent among young sexually active females, have serious sequelae, and are mostly asymptomatic. Screening and treatment of infected females has been demonstrated to prevent sequelae such as pelvic inflammatory disease.

GOAL

To assess prevalence and risk factors for chlamydia infection in US Army female recruits, whether these changed over time, and to examine variables contributing to any observed patterns.

STUDY DESIGN

Prevalence study of 23,010 non-healthcare-seeking female Army recruits enrolled in a chlamydia screening program at Fort Jackson, SC, from January 1996 through June 1999. Each of the 4-year cohorts was examined separately for prevalence and risk factors.

MAIN OUTCOME MEASURES

Urine-based testing for C trachomatis by ligase chain reaction was used to determine prevalence, and questionnaires were used to collect demographic and risk information. State home of record for each recruit was transformed into Public Health reporting region: West, Midwest, South, Northeast, and Territories.

RESULTS

Prevalence for all years was 9.51%, but a progressive increase from 8.51% to 9.92% occurred over the course of study (P=0.018). The proportion of individuals reporting specific risk factors during the 90 days preceding the study generally decreased over time. In a regression model, significant risk factors for infection included black race, age 25 years or younger, home-of-record from the South, being screened during years 3 and 4 of the study, more than one sex partner, a new sex partner, and history of any sexually transmitted disease. Condom use was protective. In another model controlling for age and home-of-record from the South, being screened in years 2, 3, and 4 of the study were significantly predictive for being chlamydia positive.

CONCLUSION

A high and slightly increasing prevalence of C trachomatis infection was observed among young females entering the military over 4 consecutive years. Young age, black race, home-of-record from the South, more than one sex partner, a new sex partner, condom use, and a history of having a sexually transmitted disease were correlates of chlamydia infection. Sustained high rates of C trachomatis infection in this population provide clear justification for a chlamydia control program for young women entering the Army consisting of screening at entry on the basis of age and possibly home-of-record together with continued periodic rescreening.

SUMMARY

A study of 23,010 female Army recruits demonstrated that a high prevalence of C trachomatis was sustained during 4 years of observation. Year of study, young age, and being from the South were significant predictors of infection.

Impact of urine collection order on the ability of assays to identify Chlamydia trachomatis infections in men

BACKGROUND

Noninvasive urine samples have been used to diagnose Chlamydia trachomatis infections, with the assumption that the first-void urine (FVU), defined as the first 20 to 30 ml at any micturition, would be the optimal collection. We compared testing technologies on first, second, and third volumes for diagnosis.

GOAL

The goal was to test in nonculture assays three sequential volumes of urine from men also undergoing urethral swabbing for C trachomatis culture specimens.

STUDY DESIGN

A total of 237 men attending an STD clinic (C trachomatis prevalence, 11%) collected three containers of urine (each containing 20-30 mL) for testing in four nonculture assays. A urethral swab specimen was tested in cell culture.

RESULTS

The numbers of men positive by testing of FVU with nucleic acid amplification (LCx chlamydia), nucleic acid hybridization (PACE 2), enzyme immunoassay (Chlamydiazyme), and a leukocyte esterase dipstick were 26, 7, 14, and 11, respectively; urethral culture identified 6 of the infected men. Comparative testing of all voids from the 26 men positive by the FVU assays demonstrated a reduction of LCx-positives. Non-amplified-test positivity declined precipitously in subsequent voids, approaching zero in the third void. The presence of symptoms and time of last void up to 8 hours had little effect on the number of positives detected by LCx of FVU.

CONCLUSION

Amplified testing of FVU was most effective for diagnosing infection in these men.

Diagnosis of Chlamydia trachomatis infections in a sexually transmitted disease clinic: evaluation of a urine sample tested by enzyme immunoassay and polymerase chain reaction in comparison with a cervical and/or a urethral swab tested by culture and polymerase chain reaction

OBJECTIVE

To evaluate the value of a urine sample for diagnosing Chlamydia trachomatis infection in an STD clinic in a prospective study of samples collected from 410 consecutive STD patients (167 female and 243 male).

METHODS

Urine samples were tested by enzyme immunoassay (EIA) and polymerase chain reaction (PCR) in comparison with cervical and/or urethral swabs tested by PCR and cell culture. A questionnaire was completed for a total of 320 patients concerning symptoms, and determining whether they were controls, contacts or were being tested subsequent to legal abortion.

RESULTS

The overall prevalence of C. trachomatis infection was 11.5%. At least 40% of patients were asymptomatic. Of the C. trachomatis-positive patients, 85% were diagnosed by testing urine, compared to 91% by testing swabs. For urine tests, the sensitivities of PCR were 66.7% and 71.9% for female and male patients, respectively, and the sensitivities of EIA were 40.0% and 62.5%, or 46.7% and 71.9%, for female and male patients, respectively, by including a 30% gray zone below the cut-off value. For swabs, the sensitivities of PCR were 93.3% and 87.5% for female and male patients, respectively, and equal to the sensitivities of culture. In total, 3.3% of controls and 35% of contacts were found to be C. trachomatis positive.

CONCLUSION

The use of urine samples for the diagnosis of C. trachomatis infections was effective, but urine samples should be additional to conventional swab(s) instead of replacing. Partner notification and a confirmation of cure is recommended.

Effectiveness of a mobile medical van in providing screening services for STDs and HIV

This retrospective study assesses the efficacy of a mobile medical van in screening high risk individuals and identifying new cases of HIV and other sexually transmitted diseases (STDs) in an urban setting from July 1996 through March 1997. High risk sex and drug use were common, while consistent condom use was rare. Relatively few patients were screened for STDs; positive cases represented only a small proportion of the STD cases identified in the study community. The mobile program, however, accounted for 11.5% of all HIV tests conducted at public test sites in the city. Mobile medical programs have the potential to improve STD and HIV control efforts by providing services to high risk individuals who may lack access to care elsewhere. Doing so, however, will require more active case finding techniques, including new, less invasive techniques to test asymptomatic individuals.

Follow-up, treatment, and reinfection rates among asymptomatic chlamydia trachomatis cases in general practice

BACKGROUND

Adequate treatment and follow-up of patients is essential to the success of a screening programme for Chlamydia trachomatis. There has been a lack of data on follow-up, confirmation of infections, and reinfection rates among asymptomatic patients in general practice.

AIM

7b study the rates of diagnostic confirmation of C trachomatis infection, successful treatment, and reinfection one year after cases were detected in a screening programme for asymptomatic infections.

DESIGN OF STUDY

Prospective cohort study

SETTING

Fifteen general practices in Amsterdam, The Netherlands.

METHOD

One hundred and twenty-four patients with asymptomatic C trachomatis infections were requested to provide a cervical or urethral swab and a urine specimen, for the purpose of diagnostic confirmation before being treated. One year after the first screening, all of the patients were invited for a second screening. All samples were tested using the ligase chain reaction (Abbott Laboratories, Chicago, USA).

RESULTS

Out of 124 patients, 110 (89%) attended the scheduled appointment for diagnostic confirmation and treatment; 92 (84%) of them were confirmed to be positive and received treatment. At the second screening a year later, none of the 56 patients who had received treatment and who had been screened a second time were reinfected.

CONCLUSION

No asymptomatic patients werefound to have reinfections with C trachomatis one year after diagnostic confirmation and treatment. This underlines the effectiveness of the screening and treatment strategy

Molecular methods for diagnosis of infective endocarditis

The culture of viable microorganisms from the blood or from cardiac tissue is currently the most important test for diagnosis of IE. This is followed by phenotypic identification methods used for taxonomic positioning of isolates. However, in those cases where the invading microorganism is difficult or impossible to culture (including instances of prior antimicrobial treatment), molecular methods provide the best means for detection. Molecular identification methods, either nucleic acid target or signal amplification alone or in combination with sequence analysis can offer a more specific and in some cases a more rapid alternative to the phenotypic methods. We propose revised Duke criteria of IE, including positive identification of an organism by molecular biology methods.

Use of the ligase chain reaction on urine of men and their female sexual partners for detection of genital Chlamydia trachomatis infection

OBJECTIVE: The purpose of the present study was to evaluate an in vitro DNA amplification assay named the ligase chain reaction (LCR) for the detection of Chlamydia trachomatis cryptic plasmid DNA in urine from men and women, in comparison with urethral swab culture in men and cervical swab culture in women. METHODS: 591 patients (394 men with urethritis and 197 female sex partners) attending a center for sexually transmitted diseases in northern Italy between January 1994 and January 1995 were enrolled in this study. A cervical swab was collected from women and a urethral swab from men for standard tissue cell culture. From each patient 20 mL of the first stream of the urine (FVU), taken at least 2 h after the last urination, were collected for LCR analysis. Discrepant results were further analyzed by direct fluorescence and a LCR with alternative primers. RESULTS: In men the prevalence of C. trachomatis infection by urethral culture was 13.45% and, after resolution of discordant results, the LCR method performed on FVU showed a sensitivity, specificity, positive predictive value and negative predictive value of 89.4%, 100%, 100% and 98.2%, respectively; the sensitivity of tissue cell culture was 92.8%. In female sex partners, the prevalence of C. trachomatis infection by cervical culture was 3.04%; LCR detected eight true positive samples, two more than tissue cell culture, and no false-negative results. CONCLUSION: LCR analysis of FVU is a rapid, non-invasive technique and represents a good alternative to tissue cell culture. Further study is needed to investigate possible LCR inhibitors present in urine samples.

Use of ligase chain reaction for laboratory identification of Chlamydia trachomatis and Neisseria gonorrhoeae in adolescent women

STUDY OBJECTIVE

To compare the ligase chain reaction (LCR) with culture for the detection of Neisseria gonorrhoeae (GC) and with culture and direct fluorescent antibody (DFA) for identification of Chlamydia trachomatis (CT) in cervical specimens from adolescent women.

DESIGN

A prospective study of test performance.

SETTING

Two urban, hospital-based adolescent clinics.

PARTICIPANTS

Adolescent women aged 12-22 yr undergoing pelvic examination for routine sexually transmitted disease (STD) screening or symptoms suggestive of an STD.

MAIN OUTCOME MEASURES

LCR results were considered to be true positives if confirmed by culture and/or DFA (CT only). Discrepant LCR results were confirmed by testing an alternative locus.

RESULTS

With 538 subjects, LCR for CT had a sensitivity of 98.4% (61/62) and specificity of 96.4% (459/476) prior to resolution and a sensitivity of 98.6% (70/71) and specificity of 99.6% (459/461) after resolution. With 1225 subjects, LCR for GC had a sensitivity of 90.0% (54/60) and specificity of 99.4% (1158/1165) prior to resolution and a sensitivity of 90.6% (58/64) and specificity of 100% (1158/1158) after resolution. CT culture alone identified 80% of the true positives and DFA alone only identified 72%. GC culture alone identified 94% of the true positives.

CONCLUSIONS

LCR is an extremely sensitive and specific rapid test, utilizing a single swab and convenient room-temperature storage and transport of specimens. LCR testing of cervical specimens for CT in adolescent women is a better test for detecting CT infection than culture or DFA. LCR testing for cervical GC infection may provide an advantage over culture in circumstances in which optimal transport conditions and viability of the organism cannot be assured.

PNA for rapid microbiology

The acceptance of rRNA sequence diversity as a criterion for phylogenetic discrimination heralds the transition from microbiological identification methods based on phenotypic markers to assays employing molecular techniques. Robust amplification assays and sensitive direct detection methods are rapidly becoming the standard protocols of microbiology laboratories. The emergence of peptide nucleic acid (PNA) from its status as an academic curiosity to that of a promising and powerful molecular tool, coincides with, and complements, the transition to rapid molecular tests. The unique properties of PNA enable the development of assay formats, which go above and beyond the possibilities of DNA probes. PNA probes targeting specific rRNA sequences of yeast and bacteria with clinical, environmental, and industrial value have recently been developed and applied to a variety of rapid assay formats. Some simply incorporate the sensitivity and specificity of PNA probes into traditional methods, such as membrane filtration and microscopic analysis; others involve recent techniques such as real-time and end-point analysis of amplification reactions.

Strategies for signal amplification in nucleic acid detection

Many aspects of molecular genetics necessitate the detection of nucleic acid sequences. Current approaches involving target amplification (in situ PCR, Primed in situ Labeling, Self-Sustained Sequence Replication, Strand Displacement Amplification), probe amplification (Ligase Chain Reaction, Padlock Probes, Rolling Circle Amplification) and signal amplification (Tyramide Signal Amplification, Branched DNA Amplification) are summarized in the present review, together with their advantages and limitations.

Cost effectiveness analysis of a population based screening programme for asymptomatic Chlamydia trachomatis infections in women by means of home obtained urine specimens

OBJECTIVES

To evaluate the cost effectiveness of a systematic screening programme for asymptomatic Chlamydia trachomatis infections in a female inner city population. To determine the sensitivity of the cost effectiveness analysis to variation in the probability of developing sequelae.

METHODS

A decision tree was constructed to evaluate health effects of the programme, such as averted sequelae of chlamydial infection. Cost effectiveness from a societal perspective was estimated for screening by means of a ligase chain reaction on mailed, home obtained urine specimens, in a population with a C trachomatis test prevalence of 2.9%. An extensive sensitivity analysis was performed for the probability of sequelae, the percentage of preventable pelvic inflammatory disease (PID), and the discount rate.

RESULTS

The estimated net cost of curing one woman, aged 15-40 years, of a C trachomatis infection is US$1210. To prevent one major outcome (PID, tubal factor infertility, ectopic pregnancy, chronic pelvic pain, or neonatal pneumonia), 479 women would have to be screened. The net cost of preventing one major outcome is $15 800. Changing the probability of PID after chlamydial infection from 5% to 25% decreases the net cost per major outcome averted from $28 300 to $6380, a reduction of 78%. Results were less sensitive to variations in estimates for other sequelae. The breakeven prevalence of the programme ranges from 6.4% for the scenario with all probabilities for complications set at the maximum value to a prevalence of 100% for probabilities set at the minimum value.

CONCLUSIONS

Systematic screening of all women aged 15-40 years for asymptomatic C trachomatis infections is not cost effective. Although the results of the analyses are sensitive to variation in the assumptions, the costs exceed the benefits, even in the most optimistic scenario.

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.

Comparison of the urine-based ligase chain reaction test to culture for detection of Chlamydia trachomatis and Neisseria gonorrhoeae in pediatric sexual abuse victims

BACKGROUND

The urine-based ligase chain reaction (LCR) assay for Chlamydia trachomatis and Neisseria gonorrhoeae is an attractive alternative to culture because of the relative ease with which specimens may be collected, transported and processed. In addition LCR offers superior sensitivity while maintaining high specificity when compared with culture in various studies of adolescents and adults. A study comparing LCR to culture has not been published concerning children.

METHODS

We conducted a prospective, comparison trial of the urine-based LCR test for Chlamydia trachomatis and Neisseria gonorrhoeae as compared with culture among children at a specialized referral center for evaluation for alleged sexual assault. Of the 1,010 children presenting to the center during the study period, 164 met the study requirements for risk of a sexually transmissible disease and collection of both culture and urine LCR specimens.

RESULTS

Eight specimens tested positive by both methods for C. trachomatis. Another 10 specimens tested positive for C. trachomatis by LCR but were negative by culture. No patient with a negative LCR for C. trachomatis had a positive culture. For N. gonorrhoeae 2 specimens tested positive by both methods, and 3 specimens tested positive by LCR but negative by culture. No patient with a negative LCR for N. gonorrhoeae had a positive culture.

CONCLUSIONS

The low prevalence of disease in the study population precluded statistical analysis. LCR may prove to be as specific and more sensitive than culture for the detection of C. trachomatis and N. gonorrhoeae in children. Further studies are needed.

Comparative model-based analysis of screening programs for Chlamydia trachomatis infections

The design of a screening program for asymptomatic genital infections with Chlamydia trachomatis, requires decisions about which sex or age group should be targeted and whether partner referral should be included in the program. To investigate the effects of various screening programs on the prevalence and incidence of asymptomatic C. trachomatis infections in women, in May 1996 to April 1997 in Bilthoven, the Netherlands, the authors used a stochastic simulation model for C. trachomatis transmission in an age-structured, heterosexual population with a sexually highly active core group. Different screening scenarios were implemented over a time period of 10 years. Prevalence, incidence, and the fraction of infected persons found by partner referral were computed. Through screening of men and women between ages 15 and 24 years (baseline scenario), the prevalence of asymptomatic infections in women could be reduced from 4.2% to 1.4% in 10 years. Increasing the age range of screening up to ages 29 or 34 years led to prevalences of 0.4% and 0.06%, respectively, after 10 years. About 28% of all infected persons were found via partner referral. There are considerable indirect positive effects of screening on those population groups that are not included in the screening because of the reduced risk of becoming infected. Partner referral contributes substantially to prevalence reduction.

Low diagnostic accuracy of selective screening criteria for asymptomatic Chlamydia trachomatis infections in the general population

OBJECTIVES

To develop and validate selective screening criteria for asymptomatic Chlamydia trachomatis infections in the general population.

METHODS

11,505 people, aged 15-40 years, registered in 16 general practices in Amsterdam were invited to return by mail a home obtained first void urine sample and a questionnaire. Participants were randomly allocated into a development group (75%) or a validation group (25%). C trachomatis infection was determined by the ligase chain reaction. In the development group a set of criteria was identified by means of stepwise logistic regression analysis. The diagnostic accuracy (area under the ROC curve; AUC) and sensitivity, and the corresponding percentage of people selected for screening were calculated. The criteria developed in this study were applied to the validation group.

RESULTS

The prevalence of asymptomatic C trachomatis infections among men was found to be 2.4% (1.7-3.0), and among women 2.8% (2.2-3.4). Screening men, based on Surinam/Antillean origin and painful micturition, yielded an AUC of 0.58 (0.55-0.60). Screening women, based on Surinam/Antillean origin, new sex partner in the previous 2 months, and unmarried/not cohabiting, yielded an AUC of 0.67 (0.65-0.69). Application of the criteria for men to the validation group yielded an AUC of 0.53 (0.48-0.57); by screening 10% of the men, 15% of the cases were detected. The AUC of the criteria for women in the validation group was 0.58 (0.54-0.61); by screening 51% of the women, 63% of the cases were detected.

CONCLUSION

The prevalence of asymptomatic C trachomatis infections in Amsterdam is less than 3%. No suitable selective screening criteria for the general population could be identified.

Cost-effectiveness of screening programs for Chlamydia trachomatis: a population-based dynamic approach

BACKGROUND

Models commonly used for the economic assessment of chlamydial screening programs do not consider population effects.

GOAL

To develop a novel dynamic approach for the economic evaluation of chlamydial prevention measures and to determine the cost-effectiveness of a general practitioner-based screening program.

STUDY DESIGN

The dynamic approach was used to estimate the cost-effectiveness of a screening program for the first 10 years of screening in The Netherlands. Screening involved a ligase chain reaction test on urine followed by standardized therapies and partner referral. Eligible persons were sexually active, 15 to 24 years, visited a general practitioner, and had no symptoms of sexually transmitted diseases. The heterosexual model population, which consisted of persons 15 to 64 years, had a total chlamydial prevalence of 4.1% before screening. Screening effects on chlamydial incidence were computed by using a population-based stochastic simulation model. Incidence data were connected with a decision analysis model to determine the health effects of the program. The net costs of the program were calculated (investment costs minus averted costs, in 1997 US$) from a societal perspective and expressed per major outcome averted (symptomatic pelvic inflammatory disease, chronic pelvic pain, ectopic pregnancy, infertility, neonatal pneumonia).

RESULTS

Unlike the standard static approach, our model adequately addresses dynamic processes such as chlamydial transmission and the impact of screening programs on chlamydial incidence in the population. During the first 10 years of screening, the investigated program yields savings of US $492 or US $1,086 per major outcome averted, excluding or including indirect costs, respectively. These results depend on chlamydial prevalence and partner referral.

CONCLUSIONS

The cost-effectiveness of chlamydial screening programs seems best to be determined by using dynamic modeling on a population basis. In addition to preventing negative health outcomes, the investigated screening program may save costs.

Assessment of Chlamydia trachomatis prevalence by PCR and LCR in women presenting for termination of pregnancy

OBJECTIVES

To determine the prevalence of Chlamydia trachomatis in a patient population presenting for legal termination of pregnancy by polymerase chain reaction (PCR) and ligase chain reaction (LCR), from first catch urine and self administered tampons, and comparing with the traditionally collected endocervical swab tested by both PCR and culture.

METHODS

Consecutive women attending for legal termination of pregnancy were screened for chlamydia by patient collected first catch urine and tampon, and physician collected endocervical swab.

RESULTS

Of 1175 patients with complete samples, there were 33 (2.8%) in whom chlamydia was detected by two or more assays from one or more sample site. Chlamydia was detected equally well by both PCR and LCR in first catch urine (p = 0.25), tampon (p = 0.5), and endocervical swab (p = 0.5). However, both PCR and LCR were significantly better than culture of an endocervical swab (p = 0.0005) for detection of C trachomatis.

CONCLUSION

The prevalence of chlamydia in patients presenting for termination of pregnancy was 2.8%. A simple efficient way of performing screening for chlamydia for women presenting for termination of pregnancy is by first catch urine or tampon, which can be tested by the highly sensitive amplification assays, PCR or LCR.

Multicenter evaluation of the AMPLICOR and automated COBAS AMPLICOR CT/NG tests for detection of Chlamydia trachomatis

The fully automated COBAS AMPLICOR CT/NG and semiautomated AMPLICOR CT/NG tests were evaluated in a multicenter trial for the ability to detect Chlamydia trachomatis infections. Test performance compared to that of culture was evaluated for 2,236 matched endocervical swab and urine specimens obtained from women and for 1,940 matched urethral swab and urine specimens obtained from men. Culture-negative, PCR-positive specimens that tested positive in a direct fluorescent-antibody test or in a confirmatory PCR test for an alternative target sequence were resolved as true positives. The overall prevalences of chlamydia were 2.4% in women and 7.2% in men. The COBAS AMPLICOR and AMPLICOR formats yielded concordant results for 98.1% of the specimens. With the infected patient as the reference standard, the resolved sensitivities of COBAS AMPLICOR were 89.7% for endocervical swab specimens, 89.2% for female urine specimens, 88.6% for male urethral swab specimens, and 90.3% for male urine specimens. When results were analyzed as if only a single test had been performed on a single specimen type, the resolved sensitivity was always higher. The resolved specificities of PCR were 99.4% for endocervical swab specimens, 99.0% for female urine specimens, 98.7% for male urethral swab specimens, and 98.4% for male urine specimens. The internal control revealed that 2.4% of the specimens were inhibitory when initially tested. Nevertheless, valid results were obtained for 98.6% of the specimens because 59.1% of the inhibitory specimens were not inhibitory when a second aliquot was tested. The COBAS AMPLICOR and AMPLICOR CT/NG tests for C. trachomatis exhibited equally high sensitivity and specificity with both urogenital swab and urine specimens and thus are well suited for screening for C. trachomatis infection.

Discrepant analysis: a biased and an unscientific method for estimating test sensitivity and specificity

Discrepant analysis is a widely used technique for estimating test performance indices (sensitivity, specificity, etc.) of DNA-amplification tests for detecting infectious diseases. It has recently been claimed that the discrepant analysis-based estimates of specificity are typically less biased than those based on culture and that the discrepant analysis-based specificity shows little appreciable bias. In this article, I show that those conclusions are incorrect. Using a typical example from the published literature, I show that the discrepant analysis-based estimates of sensitivity and specificity can generate a significant and clinically important overestimation of the true sensitivity and specificity values. Moreover, I demonstrate that the concept of discrepant analysis is profoundly flawed and unscientific. It violates a fundamental principle of diagnostic testing-the principle that the new test should not be used to determine the true disease status. Thus, the major problem with discrepant analysis is not only that it is biased but that it is unscientific. Therefore, discrepant analysis should not be adopted for the evaluation of any diagnostic or screening test.

Determination of Chlamydia trachomatis prevalence in an asymptomatic screening population: performances of the LCx and COBAS Amplicor tests with urine specimens

This study determined the performances of the LCx (Abbott) and COBAS Amplicor (Roche) tests with urine specimens for the detection of Chlamydia trachomatis in an asymptomatic screening population. Randomly selected women and men (age range, 15 to 40 years) registered in 20 general practices in Amsterdam, The Netherlands, were invited to participate in this study. Urine specimens (n = 2, 906; 1,138 specimens from men and 1,717 specimens from women) were tested for C. trachomatis by the COBAS Amplicor (Roche) and LCx (Abbott) tests. Samples which were positive by only one assay were subjected to discrepant analyses by a third assay (in-house plasmid PCR). By the LCx assay C. trachomatis DNA was detected in urine specimens from 46 of 1,717 women and 29 of 1,138 men, while the COBAS Amplicor detected C. trachomatis DNA in 52 and 35 specimens, respectively. When comparing the LCx and COBAS Amplicor tests, 32 test results (20 for women and 12 for men) were discrepant. After discrepant analyses the following sensitivities, specificities, and positive predictive values were found for the LCx and COBAS Amplicor tests: 78.6 versus 98.8%, 99.7 versus 99.9%, and 88.0 versus 95.4%, respectively. No prominent differences were found between men and women with regard to the test performances. After discrepant analyses the overall prevalences of C. trachomatis in women and men were 3.0 and 2.8%, respectively. For both women and men the prevalence in the younger age groups was higher than that in the older age groups. In conclusion, the COBAS Amplicor tests shows better diagnostic characteristics than the LCx assay for the detection of C. trachomatis in urine specimens from an asymptomatic screening population. In this asymptomatic population the overall prevalence of C. trachomatis was 2.9%.

Application of nucleic acid amplification in clinical microbiology

The use of nucleic acid amplification methods in routine clinical microbiology laboratories is becoming increasingly widespread. The theory of polymerase chain reaction is described, including discussion of suitable microbal targets, extraction of nucleic acid from clinical samples, choice of primers, optimization of the process, laboratory design, contamination, and other problems as well as quality control. Other nucleic acid amplification methods such as ligase chain reaction, self-sustained sequence replication, strand displacement amplification, and branched DNA signal amplification are described and the choice of technology is discussed.

Comparison of the PACE 2 assay, two amplification assays, and Clearview EIA for detection of Chlamydia trachomatis in female endocervical and urine specimens

Screening for sexually transmitted diseases (STDs) in a greater proportion of sexually active patients has become an accepted protocol by most health care providers. The purpose of this study was to compare the current test methods for detection of Chlamydia trachomatis used at the University of South Alabama, the PACE 2 assay (Gen-Probe) and the Clearview EIA (Wampole Laboratories), with two amplification technologies, the AMP CT (Gen-Probe) and LCx (Abbott) assays. In addition, a number of demographic parameters were ascertained by asking questions at the time of examination as well as for health care provider concerns and preferences. One urine and four endocervical swab specimens were collected in random order from 787 female patients attending one of four obstetrics-gynecology clinics. Eighty-seven percent of patients had no STD-related symptoms. Patients were considered positive for C. trachomatis if three or more assays (swab and/or urine) were positive. Abbott and Gen-Probe confirmed discrepant results by alternate amplified assays. A total of 66 true-positive specimens were detected by use of the combination of endocervical swabs and urine specimens. After discrepant analysis, sensitivities for endocervical swab specimens for the EIA and the PACE 2, LCx, and AMP CT assays were 50, 81, 97, and 100%, respectively. Sensitivities for the LCx and AMP CT assays with urine specimens were 98 and 81%, respectively. The prevalence of C. trachomatis was 8.4%, as determined by amplification technology. Overall, the amplification technologies were the most sensitive methods with either swab (AMP CT assay) or urine (LCx assay) specimens. The PACE 2 assay offered the advantage of a simpler and less expensive assay with acceptable sensitivity. The clearview CT EIA, while yielding a rapid in-office result, had unacceptably low sensitivity. The wide variation in performance with amplification assays with urine specimens as reported in both this study and the literature obviates the need to clarify optimal parameters for this specimen type.

Multicenter evaluation of the fully automated COBAS AMPLICOR PCR test for detection of Chlamydia trachomatis in urogenital specimens

The fully automated COBAS AMPLICOR CT/NG test for the detection of Chlamydia trachomatis was evaluated in a multicenter trial. Test performance was evaluated for 2,014 endocervical swab and 1,278 urine specimens obtained from women and for 373 urethral swab and 254 urine specimens obtained from men. Culture served as the reference test. Culture-negative, COBAS AMPLICOR-positive specimens that tested positive in a confirmatory PCR test for an alternative target sequence within the C. trachomatis major outer membrane protein gene were resolved as true positives. The overall prevalence of chlamydia was 4.3% in cervical swabs and 11.0% in urethral swabs from men. When the results for each specimen type were considered separately, the resolved sensitivities were 96.5% (83 of 86) for endocervical swab specimens, 95.1% (39 of 41) for urine specimens from women, 100.0% (41 of 41) for urethral swab specimens from men, and 94.4% (17 of 18) for urine specimens from men; the resolved specificities were 99.4% (1,912 of 1,924) for endocervical swab specimens, 99.8% (1,204 of 1,207) for urine specimens from women, 98. 5% (325 of 330) for urethral swab specimens from men, and 100.0% (236 of 236) for urine specimens from men. For the subset of patients from whom both swab and urine specimens were collected, the combined results for both specimen types were used to identify all infected patients. Using these combined reslts as criteria, the resolved sensitivities for the COBAS AMPLICOR test were 82.6% (38 of 46) for endocervical swab specimens, 84.4% (38 of 45) for urine specimens from women, 84.2% (16 of 19) for urethral swab specimens from men, and 89.5% (17 of 19) for urine specimens from men. In comparison, the sensitivity of culture was only 56.5% (26 of 46) for endocervical specimens and 63.2% (12 of 19) for urethral specimens from men. The internal control provided in the COBAS AMPLICOR test revealed that 2.9% of specimens were inhibitory when they were initially tested. Nevertheless, valid results were obtained for 99. 1% of specimens because 68.7% of the inhibitory specimens were not inhibitory when a second aliquot of the original sample was tested. Two additional COBAS AMPLICOR-positive specimens were detected by retesting inhibitory specimens. The COBAS AMPLICOR CT/NG test for the detection of C. trachomatis exhibited equally high sensitivities and specificities with both urogenital swab and urine specimens and, thus, is well-suited for use in screening.

An algorithm to detect Chlamydia trachomatis by polymerase chain reaction on specimens extracted for enzyme immunoassay

Amplification assays for detecting Chlamydia trachomatis have been shown to be more sensitive than enzyme immunoassay (EIA) by many investigators. In this study, we have developed an algorithm for performing PCR (COBAS AMPLICOR) on selected specimens extracted for EIA (ACCESS) with sample-to-cutoff (s/co) values between 0.25 and 0.99. Furthermore, we have shown that these specimens can be utilized for PCR without encountering any inhibition problems. In our investigation, 230 out of 6,558 urethral and cervical swabs submitted for C. trachomatis screening by EIA over a period of 9 months, had s/co values ranging between of 0.25 and 0.99. Ninety (39.1%) of these specimens tested positive by PCR. These specimens were stable and gave reproducible PCR results before and after storage for a period of 9 months. This testing algorithm offers an effective way of detecting C. trachomatis with selective use of PCR while increasing the sensitivity of the EIA screening system.

Evaluation of vaginal infections in adolescent women: can it be done without a speculum?

OBJECTIVE

Given that highly sensitive urine-based nucleic acid amplification tests may eliminate the need for speculum exam to diagnose gonorrhea and chlamydia cervicitis, we sought to determine if vaginal infections could be diagnosed without using a speculum.

METHODS

Matched pairs of vaginal specimens were collected from participants before and during speculum exam for diagnosis of trichomoniasis, bacterial vaginosis, and vulvovaginal candidiasis. Females age 12 to 22 years presenting to the Johns Hopkins adolescent primary care clinics who required a pelvic examination were eligible to participate. A convenience sample of 686 patients was recruited between July 1995 and August 1996. Paired vaginal specimens were evaluated with blinded microscopic evaluation. Analysis consisted of: 1) comparison of collection method sensitivities; and 2) assessment of proportions of infections detected by one method that were also detected by the other method.

RESULTS

Sensitivities of speculum and nonspeculum collection methods were 75% and 77% (difference = -2%; 95% confidence interval, -11%, 7%) for trichomoniasis, 64% and 68% (difference = -4% [-10%, 3%]) for bacterial vaginosis, and 85% and 80% (difference = 5% [-12%, 22%]) for vulvovaginal candidiasis. The speculum method identified 88% (trichomoniasis), 90% (bacterial vaginosis), and 81% (vulvovaginal candidiasis) of infections detected by the nonspeculum method. The nonspeculum method identified 91% (trichomoniasis), 95% (bacterial vaginosis), and 76% (vulvovaginal candidiasis) of infections detected by the speculum method.

CONCLUSIONS

Vaginal infections can be adequately diagnosed without a speculum. Once urine-based diagnosis of gonorrhea and chlamydia becomes well established, it may be possible to perform evaluations for uncomplicated genitourinary complaints without using a speculum.

Chlamydia trachomatis infections in female military recruits

BACKGROUND

Asymptomatic genital Chlamydia trachomatis infections in women can lead to pelvic inflammatory disease, infertility, and ectopic pregnancy. To design a chlamydia-control program, we conducted a large survey of women in the U.S. military.

METHODS

From January 1996 through December 1997, urine samples from 13,204 new female U.S. Army recruits from 50 states were screened by ligase chain reaction for C. trachomatis infection. Information on potential risk factors was obtained by questionnaire. With multivariate analysis, we identified criteria for a screening program.

RESULTS

The overall prevalence of chlamydial infection was 9.2 percent, with a peak of 12.2 percent among the 17-year-old recruits. The prevalence was 15 percent or more among the recruits from five southern states. The following risk factors were independently associated with chlamydial infection: having ever had vaginal sex (odds ratio for infection, 5.9), being 25 years of age or less (odds ratio, 3.0), being black (odds ratio, 3.4), having had more than one sex partner in the previous 90 days (odds ratio, 1.4), having had a new partner in the previous 90 days (odds ratio, 1.3), having had a partner in the previous 90 days who did not always use condoms (odds ratio, 1.4), and having ever had a sexually transmitted disease (odds ratio, 1.2). A screening program for subjects 25 years of age or less (87.9 percent of our sample) would have identified 95.3 percent of the infected women.

CONCLUSIONS

Among female military recruits, the prevalence of chlamydial infection is high. A control program that screens female recruits who are 25 years old or younger with urine DNA-amplification assays has the potential to reduce infection, transmission, and the sequelae of chlamydial infection.

Noninvasive screening for genital chlamydial infections in asymptomatic men: Strategies and costs using a urine PCR assay

OBJECTIVE

To evaluate cost saving strategies to screen for genital chlamydial infection in men using polymerase chain reaction (PCR) technology.

METHODS

Men with no urethral symptoms presenting to a sexually transmitted disease (STD) clinic were recruited. Study participants underwent a questionnaire interview. Urethral swabs were taken to perform a smear for polymorphonuclear leucocytes (PMN) and for the detection of Chlamydia trachomatis by culture and PCR. First-catch urine was collected for a leukocyte esterase test (LET) and PCR.

RESULTS

C trachomatis infection was detected in 36 of 463 (7.8%) men. LET and PMN were positive in 10 (28%) and 12 (33%) infected men, respectively. Risk factors for chlamydial infection were younger than age 25 years, LET-positive, PMN-positive and STD contact (P<0.001). The direct cost of genital chlamydial infection in men in Canada has been previously estimated at $381/case. Based on a sensitivity of 90% for urine PCR, the estimated direct cost of testing all participants to detect 32 cases was $453/case. Using risk factors recommended in the Canadian STD Guidelines (age younger than 25 years, new partner, STD contact or unprotected sex), the same number of cases would have been detected by testing only 384 men at $376/case. Using age younger than 25 years or STD contact as the screening criterion, 78% of those infected would have been detected at $259/case, and no new cases would have been detected by adding LET-positive or PMN-positive as risk factors.

CONCLUSION

Targeted screening for chlamydial infection using urine PCR assay and risk factors recommended in the Canadian guidelines could substantially reduce the cost of screening at a STD clinic setting. LET and PMN smear did not appear to be useful indicators of chlamydial infection in this population.

Use of ligase chain reaction with urine versus cervical culture for detection of Chlamydia trachomatis in an asymptomatic military population of pregnant and nonpregnant females attending Papanicolaou smear clinics

Ligase chain reaction (LCR) (Abbott Laboratories, Abbott Park, Ill.) with first-catch urine specimens was used to detect Chlamydia trachomatis infections in 465 asymptomatic military women attending clinics for routine Papanicolaou smear tests. Results were compared to results of cervical culture to determine the sensitivity of the urine LCR and the possible presence of inhibitors of amplification in pregnant and nonpregnant women. Discrepant results for LCR and culture were resolved by direct fluorescent antibody staining of culture sediments, two different PCR assays, and LCR for the outer membrane protein 1 gene. The prevalence of Chlamydia in specimens by urine LCR was 7.3% compared to 5% by culture. For 434 women with matching specimens, there were 11 more specimens positive by LCR than were positive by culture, of which all but one were determined to be true positives. There were four culture-positive, LCR-negative specimens, all from nonpregnant women. The sensitivity, specificity, and positive and negative predictive values of urine LCR after discrepant results were resolved were 88.6, 99.7, 96.9, and 99.0%, respectively. The sensitivity of culture was 71.4%. From the 148 pregnant women (prevalence by LCR, 6.8%), there were no patients who were cervical culture positive and urine LCR negative to indicate the presence in pregnant women of inhibitors of LCR. Additionally, a subset of 55 of the LCR-negative frozen urine specimens from pregnant women that had been previously processed in LCR buffer were inoculated with 5 cell culture inclusion forming units of C. trachomatis each and retested by LCR; all tested positive, indicating the absence of inhibitors of LCR in urine from these pregnant women. The use of LCR testing of urine specimens from asymptomatic women, whether pregnant or not, offers a sensitive and easy method to detect C. trachomatis infection in women.

A pilot study of the prevalence of chlamydial infection in a national household survey

BACKGROUND

The prevalence of Chlamydia trachomatis genital infection in the United States population is unknown. Using a new urine test for C. trachomatis, we conducted a pilot survey as part of the National Health and Nutrition Examination Survey III (NHANES III).

GOAL

To determine whether the prevalence of chlamydial infection in a convenience sample of NHANES participants was high enough to justify testing for C. trachomatis in a national survey.

STUDY DESIGN

NHANES III, conducted from 1988 to 1994, was based on a stratified multistage probability sample of the United States population. Non-Hispanic blacks and Mexican-Americans were oversampled. Using the ligase chain reaction assay for C. trachomatis, we tested urine from participants 12 to 39 years of age from 10 of the 89 sites of NHANES III. The prevalence of infection was calculated by racial or ethnic group.

RESULTS

We tested 1,144 study participants, of whom 65% were female, 30% were non-Hispanic blacks, and 30% were Mexican-American. Prevalence was higher for non-Hispanic blacks (7%) than for Mexican-Americans (3%) and non-Hispanic whites (2%). Prevalence was higher for women than men in non-Hispanic blacks (7% vs. 6%), Mexican-Americans (5% vs. 2%), and non-Hispanic whites (2% vs. 1%). In 15- to 19-year-old women, prevalence was 13% in non-Hispanic blacks, 11% in Mexican-Americans, and 5% in non-Hispanic whites.

CONCLUSION

The prevalence of C. trachomatis genital infection was high enough to suggest that a reliable national prevalence estimate could be obtained in a national probability sample survey.

Pooling of urine specimens for PCR testing: a cost saving strategy for Chlamydia trachomatis control programmes

OBJECTIVES

To evaluate pooling of first catch urine (FCU) specimens as a cost effective strategy for chlamydia testing.

METHODS

Mock specimens were pooled with and without dilution to determine optimal pool size and ease of work flow. The performance of the Amplicor Chlamydia trachomatis PCR assay on pooled specimens was compared with individual testing using 370 FCU specimens from asymptomatic men presenting to an STD clinic. Cost savings associated with pooling were estimated.

RESULTS

Using mock specimens, the sensitivity and specificity of the Amplicor PCR assay were not affected by pool sizes of two and five, but at a pool size of 10 decreased sensitivity due to inhibition was observed in one of five mock pools when the pooling method which involved no dilution was used. Archived FCU specimens from a study of 370 asymptomatic men were combined consecutively into 74 pools of five and tested by PCR. Of the 18 pools that contained positive specimens, 17 were PCR positive. Compared with testing FCU specimens individually, pooling resulted in a sensitivity of 95%, specificity of 100%, and a cost savings of 57% based on reduced number of tests required.

CONCLUSION

Depending on the prevalence of infection, pooling of FCU specimens for PCR testing may result in cost savings compared with testing specimens individually. Further evaluations to validate this strategy using fresh FCU specimens are needed.

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.

Comparison of Roche Cobas Amplicor and Abbott LCx for the rapid detection of Chlamydia trachomatis in specimens from high-risk patients

OBJECTIVE

To evaluate two automated amplification systems for the detection of Chlamydia trachomatis in urogenital specimens, the Cobas Amplicor (Roche Diagnostic Systems, Branchburg, NJ) and the LCx (Abbott Laboratories, Abbott Park, IL).

STUDY DESIGN

The two systems were compared testing specimens from 302 high-risk patients, including 98 female cervical swab specimens and 204 male urine specimens. The patients attended the state STD clinic in Reykjavik, Iceland, either because of symptoms or as a result of contract tracing.

RESULTS

The prevalence of C. trachomatis infection was 15.3% in women and 13.2% in men. For the male urine specimens, the sensitivity and specificity were 100% and 99.4% for the Cobas Amplicor and 74.1% and 100% for the LCx. In the cervical swabs, both systems detected all 15 true-positive specimens. The internal control used with the Cobas Amplicor detected inhibition in 2% of the male urine and 20% female cervical swabs, respectively.

CONCLUSION

The Cobas Amplicor demonstrated slightly better sensitivity than LCx in male urine specimens. Both systems offer the benefits of automation for routine diagnostic testing.

An internal control for routine diagnostic PCR: design, properties, and effect on clinical performance

We constructed internal controls (ICs) to provide assurance that clinical specimens are successfully amplified and detected. The IC nucleic acids contain primer binding regions identical to those of the target sequence and contain a unique probe binding region that differentiates the IC from amplified target nucleic acid. Because only 20 copies of the IC are introduced into each test sample, a positive IC signal indicates that amplification was sufficient to generate a positive signal from targets present at the limit of test sensitivity. The COBAS AMPLICOR Chlamydia trachomatis, Neisseria gonorrhoeae, Mycobacterium tuberculosis, and human hepatitis C virus tests exhibited inhibition rates ranging from 5 to 9%. Approximately 64% of these inhibitory specimens were not inhibitory when a second aliquot was tested. Because repeatedly inhibitory specimens were not reported as false negative and because additional infected specimens were detected during retesting, test sensitivities were 1 to 6% greater than they would have been if the IC had not been used.

Chlamydial lower genital tract infection and spontaneous abortion

OBJECTIVE

Few previous studies have examined the role that acute Chlamydia trachomatis lower genital tract infection plays in the development of spontaneous abortion. This study evaluated cervical C. trachomatis infections among 52 women experiencing spontaneous abortion and 59 controls.

METHODS

Pregnant women at less than 22 weeks of gestation who sought medical care in an emergency department in West Philadelphia were eligible for enrollment. Urine samples from enrolled women were tested for chlamydia using ligase chain reaction DNA amplification. All women were followed up to 22 weeks of pregnancy to ascertain the outcome of spontaneous abortion.

RESULTS

The proportion of women with chlamydial infection was 3.8% among spontaneous abortion cases and 8.5% among controls. After adjustment for potentially confounding factors, there was no substantial difference in the rate of chlamydial infection between women with and without spontaneous abortion (odds ratio 1.8, 95% confidence interval 0.3-10.7).

CONCLUSION

These data do not support a relationship between acute C. trachomatis infection and the development of spontaneous abortion.

Chlamydial lower genital tract infection and spontaneous abortion

OBJECTIVE

Few previous studies have examined the role that acute Chlamydia trachomatis lower genital tract infection plays in the development of spontaneous abortion. This study evaluated cervical C. trachomatis infections among 52 women experiencing spontaneous abortion and 59 controls.

METHODS

Pregnant women at less than 22 weeks of gestation who sought medical care in an emergency department in West Philadelphia were eligible for enrollment. Urine samples from enrolled women were tested for chlamydia using ligase chain reaction DNA amplification. All women were followed up to 22 weeks of pregnancy to ascertain the outcome of spontaneous abortion.

RESULTS

The proportion of women with chlamydial infection was 3.8% among spontaneous abortion cases and 8.5% among controls. After adjustment for potentially confounding factors, there was no substantial difference in the rate of chlamydial infection between women with and without spontaneous abortion (odds ratio 1.8, 95% confidence interval 0.3-10.7).

CONCLUSION

These data do not support a relationship between acute C. trachomatis infection and the development of spontaneous abortion.

Influence of endocervical specimen adequacy on PCR and direct fluorescent-antibody staining for detection of Chlamydia trachomatis infections

The cellular quality of the endocervical swab specimen used for the detection of Chlamydia trachomatis may dramatically impact the sensitivity of the diagnostic assay used. An evaluation of the adequacy of 319 endocervical swab specimens from women attending two inner-city sexually transmitted disease and family planning clinics, as well as five high school-based family planning clinics, was performed, and the resulting data were compared with the diagnostic results obtained by both Amplicor PCR and Microtrak direct fluorescent-antibody (DFA) staining. The swab from each patient was rolled across the open circular area of a DFA slide and then used to inoculate a transport tube for PCR (Roche), after which the swab was discarded. The slides were stained and examined by epifluorescence microscopy for the presence of C. trachomatis elementary bodies and for the presence and number of cell types to determine specimen adequacy. Cellular adequacy for a cervical swab specimen was defined as the presence of one or more columnar epithelial or metaplastic epithelial cells or the presence of more than 100 erythrocytes per high-power microscopic field. Of the 319 specimens read by DFA, 204 (63.9%) were determined to be adequate. There were 34 (10.7%) positive specimens by DFA and/or PCR. Twenty-nine (9.1%) specimens were positive by PCR, 20 (6.3%) specimens were DFA positive, and 15 (4.7%) were concordantly positive by both tests. The prevalence of chlamydia among adequate specimens was 14.2% (29/204), compared to 4.3% (5/115) for inadequate specimens (P < 0.0001). Variations in specimen quality and the sensitivity of the diagnostic assay used have a significant impact on determining the prevalence of C. trachomatis in a population.

Evaluation of 2-SP transport medium for detection of Chlamydia trachomatis and Neisseria gonorrhoeae by two automated amplification systems and culture for chlamydia

AIMS

To assess the performance of 2-sucrose-phosphate based transport medium (2-SP) for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae by an automated commercial polymerase chain reaction (PCR) and ligase chain reaction (LCR) compared to centrifugation culture on McCoy cells for C trachomatis. Second, to compare both amplification systems for initial diagnostic testing of a low prevalence population for sexually transmitted diseases.

METHODS

Four hundred and eighty one consecutive urogenital and conjunctival specimens were examined. All tests were performed on the same specimen collected with a dacron swab and transported in 2-SP medium. Samples that were positive by culture or by both PCR and LCR were considered to be true positives.

RESULTS

The prevalences of C trachomatis and of N gonorrhoeae were 2.7% and 0.4%, respectively. PCR had a resolved sensitivity and specificity of 100% and 99.8%, respectively, for C trachomatis, and 100% and 98.9%, respectively, for N gonorrhoeae. LCR was 100% sensitive and specific for both pathogens. The resolved sensitivity of the shell vial assay was 85%. No culture positive sample would have been missed by PCR or LCR. The inhibition rate for PCR was 4.8%.

CONCLUSIONS

2-SP medium proved to be suitable for both PCR and LCR. It is not limited to any one test manufacturer and allows the performance of amplification techniques and viral and chlamydia culture from the same specimen. The LCR was more reliable than PCR on initial testing. However, hands on time is longer, and no amplification control is available for LCR.