New diagnostic tests for gonorrhea and chlamydia

INFECTIOUS DISEASESUPDATE

NEW DIAGNOSTIC TESTS FOR GONORRHEA AND CHLAMYDIA Gregory J. Locksmith,

MD

ELSEVIER

Genitourinary infections caused by Neisseria gonorrhoeae and Chlamydia trachomatis pose significant public health problems in this country. Our ability to e$ectively screen for, and prevent the spread of, these organisms depends on the availability of accurate and e@cient detection methods, Culture has been the traditional reference standard for both organisms and has the advantage of 100% specificity. Gonorrhea culture is very inexpensive, whereas chlamydia culture is moderately expensive. The disadvantages of culture include variable sensitivity, complex logistics, and slow turnaround times. Antigen detection methods, such as directfluorescent antibody testing and enzyme immunoassay, have fast turnaround times and simplified logistics but lower sensitivity than culture. Recently developed tests using nucleic acid technology ogler the potential for improved sensitivity, ease of handling, and rapid processing at costs comparable to, or less than, antigen detection methods. Hybridization techniques utilize fluorescent DNA probes that bind directly to species-specific ribosomal RNA. The polymerase chain reaction (PCR) and ligase chain reaction (LCR) amplify species-specific DNA sequences prior to detection. The hybridization techniques are the least expensive and appear to have similar accuracy to PCR and LCR. Polymerase chain reaction and LCR may be performed on From the Department of Obstetrics ogy. University of Florida College Gainesville. Florida.

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first-catch urine samples, which offer the advantages of ease of collection and greater yield of Urine samples typiorganisms. cally contain organisms inhabiting both the urethra and endocervix, whereas endocervical specimens do not contain organisms in women who are colonized solely in the urethra. Endogenous inhibitors limit the sensitivity of the amplification techniques. If their e#ect could be eliminated, PCR and LCR wouldprovide clear clinical advantages over any of the other methods in use. (Prim Care Update OblGyns 1997;4: 161-167. 0 1997 Elsevier Science Inc. All rights reserved.)

Neisseria gonorrhoeae and Chlamy&a trachomatis are the two most common sexually transmitted bacterial pathogens in the United States. An estimated 1 million new infections with N gonorrhoeae occur in the United States annually.’ C trachomatis is the most common bacterial sexually transmitted disease in this country, with an estimated incidence of 4 million infections per year and associated annual direct and indirect costs of more than $2.4 billion.’ The true incidence of chlamydial infection is probably higher because reporting is not required in all states. Infections with these organisms are particularly prevalent in adolescents and young adults. Among women, endocervical infections with Ngonorrhoeae and C trachomatis are often asymptomatic and, if untreated, may result in more serious sequelae, such as pelvic inflammatory disInc..

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reserved.

1068-607X/97/$17.00

ease, ectopic pregnancy, and infertility. Pregnant women harboring these organisms typically are protected from ascending infection but are at risk of transmitting either of these organisms to their infants during birth.l The Centers for Disease Control and Prevention have recommended routine testing for C trachomatis in settings where care is provided to large numbers of young women. Screening is recommended for the following groups:”

11 All women with mucopurulent cervicitis active women 2) All sexually younger than 20 years of age 3) Women 20-24 years of age who meet either of two of the following criteria or women older than 24 years of age who do not consistently use barrier contraception and who have had a new sex partner during the previous 3 months Given the high prevalence of infections caused by C trachomatis and N gonorrhoeae, their potential for causing serious sequelae, the likelihood of infection being subclinical, and the success of inexpensive antibiotics in treating these infections, widespread screening for these organisms is beneficial. The key to effectively screening for, and preventing the spread of, these organisms rests on the ability to diagnose infections accurately, rapidly, and inexpensively.

Culture Traditionally, the standard against which all other tests for chlamydia

. PII slofi8-so7x(97)rJoo44-9

161

LOCKSMITH Table 1. Chlamydia

Definitions

of Performance

of Diagnostic

Tests for Gonorrhea

Statistic

Definition

Sensitivity Specificity Positive Negative

predict

value

predictive

value

Proportion of those Proportion of those negative Proportion of those infection Proportion of those have infection

and gonorrhea have been measured has been culture.1.3 Definitions of the statistics commonly used to measure the performance of diagnostic tests are reviewed in Table 1. Culture is the preferred method when the diagnosis is problematic and in cases of suspected sexual assault or abuse. The main advantages of culture are high specificity and the ability to preserve the organisms for additional studies, such as antibiotic susceptibility testing. Although chlamydia culture is moderately expensive ($90*), culture for gonorrhea is very inexpensive ($15*), relative to other test methods. Culture, however, has numerous disadvantages as a screening method for these organisms. The requirements for collection, storage, and transport are stringent for either organism and are not always met, and delays of three or more days can elapse between time of collection and availability of results. The sensitivity of chlamydial culture varies from 60-90% ,4-9 depending on the prevalence of infection and the conditions surrounding sample collection, transport, and processing. The sensitivity is enhanced when well-trained clinicians collect the samples and the clinic is relatively close to the laboratory.” A major obstacle to the diagnosis of chlamydial infection by any method has been improper or inadequate sample collection. Although the organism causes a mucous membrane

infection,

*Based on outpatient University of Florida

162

and

it is an intra-

laboratory charges Shands Hospital.

at the

with infection who test positive without infection who test who test positive

who have

who test negative

who

do not

cellular pathogen that primarily infects columnar epithelial cells. Therefore, the collected specimen must contain an adequate number of infected cells. Purulent discharge is not an appropriate specimen for chlamydia detection but is often submitted. Before collecting the specimen for chlamydial cell culture, all secretions and discharge should be removed from the cervical OS. Swabs with plastic or wire shafts and tips made of cotton, rayon, or calcium alginate should be used. Swabs with wooden shafts should not be used because wood may contain substances that are toxic to ch1amydiae.l” In nonpregnant women, use of an endocervical brush rather than a swab may increase the sensitivity of culture and nonculture tests. The swab or brush should be inserted 1-2 cm into the endocervical canal, just past the squamo-columnar junction, and rotated firmly against the wall for 10-30 seconds. It then should be withdrawn without touching the surface of the vagina and placed in transport medium or used to prepare a slide for direct fluorescent antibody testing.‘” The transport requirements for chlamydial specimens are strict, and deviations from the recommended media and storage conditions decrease test sensitivity. The specimen should be transported to the laboratory immediately after collection

or stored

at 4°C if prompt

transport is not possible. If a delay in processing is unavoidable, the specimen can be stored at 4% for 48

hours. If a longer delay is anticipated, the specimen should be stored at -70°C or colder. Freezing may decrease the isolation rate by up to 20%.1° Another factor limiting the sensitivity of endocervical culture for C trachomatis is the substantial proportion of female urogenital infections affecting sites other than the endocervix. Studies have shown that 50-60% of women infected with C trachomatis have infections in both the cervix and urethra, 30% are infected in the cervix alone, and 540% are infected in the urethra a10ne.8,11 Accordingly, addition of urethral culture to endocervical culture increases the detection rate by 15-20%." The sensitivity of gonorrhea culture is approximately 80-95%.1”Z14 False negative results are attributed to inadequate specimen collection or storage, transport problems, or inhibition of growth by the components of selective media.‘” For culture of N gonorrhoeae, rayon or dacron tipped swabs should be used to collect the specimen. The organism has fastidious growth requirements, so the culture sample must be immediately plated on an agar medium and transported to a chamber that provides a CO,enriched atmosphere. Specimens from nonsterile sites require a selective medium, such as ThayerMartin agar, that prevents overgrowth by other more rapidly growing species. The organism is identified by direct visualization under the microscope and detection of oxidase and catalase positivity.

Enzyme Immunoassay In recent years, the enzyme immunoassay (EIA) antigen detection technique had been the most commonly used nonculture diagnostic laboratories

method in handling

large numbers of chlamydial speciEIA employs enzymemens?’ Prim

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NEW DIAGNOSTIC TESTS

labeled monoclonal or polyclonal antibodies to detect chlamydial lipopolysaccaride (LPS). The specimen is added to one of two solid phase systems or a membrane system. The antibody binds to the chlamydial antigen, and the bound enzyme converts a colorless substrate into a colored product. The absorbance of the reaction mixture is measured with a spectrophotometer at 450 nm wavelength. Total processing time ranges from 15-30 minutes for membrane systems to 3-4 hours for solid phase systems. Both systems are commercially available.4.‘fi The main advantages of EIA are the objective interpretation of its results, rapidity, and ease of use, particularly for batching and interpreting large volumes.* The sensitivity of EIA varies from 65-95%, with culture as the reference standard. Its sensitivity is considered to be satisfactory in high-risk populations, such as in individuals with mucopurulent cervical discharges, sexually transmitted disease clinics, and other sites where the prevalence of Ctrachomatis is high.‘.“,” The main disadvantage of EIA is its inadequate sensitivity in low-risk populations. Additionally, the assay is likely to be inadequate in detecting recently acquired chlamydial infections and in posttreatment tests of cure, where the amount of infective particles may be 1ow.l” The specificity of EIA for chlamydia is 95% or greater. False positive results are due primarily to cross reactivity of the antibodies with common micro-organisms, such as Staphylococcus aureus, group B streptococci, and a variety of gram-negative organisms.lF Although 95% specificity seems to suggest a low false positive rate, this 5% figure becomes accentuated in low-risk populations, where the false positives can actually outnumber the true positives.‘” Considering the potential serious social ramifi-

cations of false positive tests for sexually transmitted diseases, EIApositive specimens require verification, usually with direct fluorescent antibody staining or EIA directed toward a different antigen. Verification will virtually eliminate false positive results, but it adds labor and cost.‘” Enzyme immunoassay for detection of N gonorrhoeae is commercially available for urethral swab specimens in men and endocervical swab specimens in women. As with EIA for detection of chlamydia, its usefulness is hampered, most notably in low-risk populations, by its 80% sensitivitv and 95% specifici4.14 ty*

Direct Fluorescent Anti body The first nonculture chlamydia method developed was the Direct Fluorescent Antibody (DFA) test. Its main advantage over culture is its total processing time of 30 - 60 minutes. By allowing direct visualization of C trachomatis elementary bodies, it permits immediate assessment of specimen adequacy. Interpretation of the smear, however, is subjective, and a certain amount of skill is required for optimal accuracy. Furthermore, DFA is not suitable for screening large numbers of samples because it is labor intensive and time consuming for the technicians, and operator fatigue and error become problematic over extended periods of time.” The DFA test makes use of monoclonal antibodies directed against species-specific antigens. Antibodies directed against the major outer membrane protein (MOMP) of C trachomatis appear to be the most specific and produce the most intense fluorescence.13 Occasionally, even these very specific antibodies stain bacteria other than C trachomatis, particularly when these specimens have been obtained from the

rectum. With cell culture as the reference standard, the sensitivity of DFA has varied from 50-80%. In general, the detection rate is greater when lower cutoff values for elementary bodies are used and in populations with a high prevalence of disease. The specificity of DFA is greater than 95%.”

Nucleic Acid Techniques Although culture, DFA, and EIA have been useful in detecting chlamydia and gonorrhea infections, the tests suffer from excessive labor intensity, complicated logistics, or suboptimal sensitivity. Newer diagnostic methods employing gene technology have the advantages of rapidity, automated technology, reasonable expense, and potential for improved sensitivity without significant loss of specificity. These methods are based on either the direct detection of organism-specific RNA sequences with nucleic acid probes (nucleic acid hybridization) or the amplification of organism-specific DNA sequences by polymerase chain reaction (PCR) or ligase chain reaction (LCR). Because the newer tests may have greater sensitivity than the existing reference standard (culture), performance evaluations on these tests are problematic. The true sensitivity of a test will be overestimated when compared to the existing reference standard if the reference standard’s sensitivity is less than 100% and the sensitivity of the test being evaluated is less than or equal to that of the reference standard, as is the case with EIA and DFA. If the sensitivity of the test being evaluated exceeds that of the reference standard, however, its measured value may be underestimated, as would its specificity. The “expanded gold standard” utilizes DFA and alternate DNA amplification tests to resolve discrepant results, namely culturenegative and nucleic acid-positive

LOCKSMITH

samples.4,” Also known as discrepant analysis, this analytic technique attempts to evaluate test performance more accurately by providing a hybrid gold standard that has a higher sensitivity than the tests being measured against it. Discrepant analysis has been criticized on grounds that it upwardly biases the performance statistics of the new test. One specific criticism is that the additional tests are limited to the samples that have discrepant results, when they should be applied to all samples. In addition, the alternate DNA amplification tests have not been approved by the U.S. Food and Drug Administration, and the independence of different amplification test method errors has never been demonstrated.17 Conversely, use of culture as the comparative gold standard clearly is inadequate because it downwardly biases the performance of the new test. Therefore, evaluations of these new tests primarily are utilizing the expanded gold standard, with some studies providing two sets of performance statistics, one set against the expanded gold standard and one set against culture.

Nucleic Acid Probes Nucleic acid hybridization tests (DNA probes) utilize chemiluminescent DNA segments that are complementary to specific sequences of C trachomatis or Ngonorrhoeae ribosomal RNA. This assay permits direct detection of the organism in urogenital and conjunctival specimens. A luminometer supplied by the manufacturer detects the labeled organisms. The most thoroughly evaluated of these assays is the Gen-Probe PACE-2 (Gen-probe, San Diego, CA).4.g The DNA probes offer the same advantages of EIA with some improvements. The assay is inexpensive and simply performed, with a 164

total processing time of 2-3 hours. Large batches of samples can be processed easily. The PACE-2 kit contains the appropriate swab and tube with transport medium.4,g The transport medium effectively stabilizes the specimens after collection, and both C trachomatis and N gonorrhoeae are collected, separately processed, and then analyzed from the same swab.5 The main disadvantage of PACE-2 is the cost of the equipment required for sample processing and detection.4 The sensitivity of PACE-2 for detecting C trachomatis ranges from 73-9fj~o.‘%.5.8.“.1” For detection of N gonorrhoeae, the sensitivity is 8599% .4.5 These estimates are at least comparable to those of culture and superior to those of EIA. The sensitivity of the DNA probes may be adversely affected by technical error or mutation. PACE-2 specificity is 9i’-100% for both organisms. 4,5~8~g~16 Most evaluations of the DNA probes have been performed in relatively high prevalence populations. In populations with lower prevalences, the sensitivity of the test may be lower and the positive predictive value will undoubtedly be lower. The importance of near 100% specificity in screening low prevalence populations cannot be overemphasized. The specificity of PACE-2 can be improved to virtually 100% when used in conjunction with a probe competition assay (PCA).4.8,16,18 This confirmatory test determines whether a positive signal is due to the presence of the organism of interest or to interfering material in the sample. Blood, dust, lint, or glove powder may bind to labeled probe, causing nonspecific chemiluminescence. In the PCA, unlabeled probe is added to the sample, which inhibits luminescence in true positive samples but will not cause a decrease in signal intensity in the false positive samples? Unlike the EIA, where a confirmatory test is required for all positive spec-

imens, PACE-2 requires PCA supplementation only for borderline positive results. Woods and Garza’* recommend that each laboratory using PACE-2 establish its own cutoff value in the positive range above which specificity would be W100% and, below which, PCA would be routinely performed.

Nucleic Acid Amplification Techniques POLYMERASE CHAIN REACTION AND LIGASE CHAIN REACTION The most recently introduced assays, which offer the greatest promise for the future, are the nucleic acid amplification techniques. Of these, the PCR and LCR have been the most extensively studied. In multiple evaluations, these assays have detected IO-20% more positive specimens than culture, without a significant decline in specificity.” The potential for greater sensitivity of the DNA amplification methods probably stems from their efficiency in detecting specimens containing either cultivable (culture positive) or noncultivable (culture negative) organisms7 and their ability to detect organisms at lower concentrations than any other method available.14.1g Another apparent advantage of the DNA amplification methods is their ability to evaluate specimens from urine as well as the female endocervix and male urethra. Previous attempts to isolate chlamydia from the urine by culture have been unsuccessful.” Although chlamydial antigen detection assays with concentrated first catch urine (FCU) have met with some success in men,” similar attempts in women have been unsuccessful.“” Polymerase chain reaction was the first commercially available amplified nucleic acid test for detection of C trachomatis.g The assay is also available for direct detection of Prim

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Ngonorrhoeae in combination with chlamydia but, in this form, it has not been evaluated extensively. The Amplicor C trachomafis assay (Roche Diagnostics, Branchburg, NJ) has been the most rigorously studied. Polymerase chain reaction technology employs three basic processes: amplification, hybridization, and detection. In the initial process, C trachomatis-specific, plasmid-based, target DNA in the specimen is amplified up to a billion-fold in a thermocycler, using biotinylated DNA primers that are complementary to the target DNA sequence.4.” The primers plus the original template serve as templates for the next cycle of hybridization. As subsequent cycles are performed, the amplification proceeds exponentially. After adequate amplification, the sample is transferred to a 96-well plate coated with oligonucleotide probes complementary to the amplified DNA sequences (amplicons). Avidin-horseradish peroxidase is added to the captured amplicons, and a calorimetric reaction ensues. The organism is detected by spectrophotometric absorbance at 450 nm. Total processing time is 4-5 hours4 Although PCR is relatively demanding and labor intensive, its cost is roughly equivalent to that of EIA or DFA. When culture has been used as the gold standard, the sensitivity of PCR for chlamydia is 89-loo%.*.' Using the expanded gold standard, PCR sensitivity is 80-97%, a figure at least equal to, and possibly more sensitive than, culture.*.‘” Specificity is 99 -100% .4.n.1D The sensitivity of PCR for detecting C trachomatis in women has been lower than expected for two main reasons. First, most of the studies evaluating PCR have used endocervical specimens. Because a substantial proportion of chlamydial infections exist only in the urethra, the endocervix alone is probably not the best source for Volume

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achieving optimal sensitivity. Second, up to 15% of clinical specimens from either the endocervix or the urine contain inhibitors of PCR amplification, leading to false negative results.8.16 Few studies to date have attempted specifically to determine the best source of material for optimizing the sensitivity of the new detection methods. The limited data available indicate that urine is superior to endocervical specimens, at least for the detection of chlamydia.‘” An explanation for this improved sensitivity is that chlamydial material originating from the cervix typically is carried with the vaginal discharge to the perineum and then into the urine. Presumably, organisms detected in the voided urine originate from both the urethra and the cervix, whereas those detected in the endocervix originate solely from the cervix.8 Although urine is not always contaminated by cervical organisms, it may be the best source for detection that currently is available. Amplification methods on urine offer clear advantages over the other methods. The sample is more easily collected than a cervical swab specimen, results are available quickly, and the sensitivity is at least equal to that of culture. Despite urine samples demonstrating a higher percentage of positive results in truly infected women, urine PCR has not shown improved detection over either culture or endocervical PCR, presumably due to endogenous PCR inhibitors in samples obtained from women. A recent large study in a low prevalence population showed the sensitivity of PCR improved from 82% to 97% on urine specimens and from 82% to 85% on endocervical specimens when dilution of the samples was performed to overcome the effect of inhibitors.* Another smaller study from a high prevalence population demonstrated that endocervical PCR sen-

TESTS

sitivity increased from 88% to 95% after specimen dilution.‘” Polymerase chain reaction assessment of either urine of endocervical specimens offers distinct advantages in low-risk screening populations because of its speed, accuracy, and ability to handle large numbers of specimens. The advantages of PCR in symptomatic populations, however, are less clear. The proportion of false negative results due to inhibitors becomes particularly important in testing symptomatic populations, where the negative predictive value of PCR may decline more than that of culture. If the effect of PCR inhibitors could be eliminated, PCR clearly would be superior to any of the nonamplified methods currently in use, regardless of the prevalence of chlamydia.” The LCR is based on the same principles as PCR with one modification designed to further improve specificity. Ligase chain reaction uses two complementary probes that, when the correct template is available, hybridize next to each other and become ligated together. The newly ligated primers plus the original template serve as templates for the next cycle of hybridization. The use of two probes may confer additional specificity in that even a one base-pair mismatch near the junction of the probes will inhibit ligation and, thus, amplification.‘” Ligase chain reaction can be performed on first-catch urine specimens and on genitourinary swabs. It has been applied for detection of C trachomatis and N gonorrhoeae. Most investigations have concentrated on detection of chlamydia in urine samples, where LCR appears to offer the most advantages. The main advantages of urine LCR over culture for detection of chlamydia are possible superior sensitivity, more rapid availability of results, and greater ease of sample collection As with PCR, LCR on endocervital swabs does not appear to offer 165

LOCKSMITH Table

2. Characteristics of Tests for Chlamydia and Gonorrhea Test

Chlamydia trachomatis Cell culture EIA

Sensitivity

(%)*

60-90 65-85

Specificity 100 95

(%)*

Cost+

Time

$92 $42

2-3 d 15 min-4 hr

DFA

50-75

96-99

$42

30-60

DNA probe

73-96

97-100*

$22

2-3 hr

PCR

80-97

99

$51

4-5 hr

LCR

86-96

99-100

$51

4-5 hr

80-95

99-100 95 97-100* 100

$15 $42 $32 $51

2-3 15 2-3 4-5

Neisseria gonorrhoeae Culture EIA DNA probe LCR

80 85-99

95-100

min

d min-4 hr hr hr

Comments

Logistically complex Large numbers of specimens processed in short amount of time Interpretation requires experience and skill: not good for large numbers Can analyze gonorrhea from same swab; good for large numbers Urine sensitivity may be higher than endocervical; good for large numbers Good for large numbers; can analyze gonorrhea from same sample Logistically complex but inexpensive See EIA above See DNA probe above See PCR and LCR above

EIA. enzyme immunoassay: DFA, Direct Fluorescent Antibody: DNA deoxyribonucleic acid: PCR. polymerase * Sensitivity and specificity calculated against an expanded gold standard. + Cost estimates based on outpatient laboratory charges at the Iinivrrsity of Florida Shands Hospital. * Specificity is optimized when borderline positive? results are verifirxi with the probe competition assay

any advantages over LCR on urine specimens. Ligase chain reaction has no proven benefit over PCR other than perhaps a greater experience with urine specimens and greater experience for detection of gonorrhea. The sensitivity of urine LCR for detection of chlamydia appears to be greater than that of cell culture when an expanded gold standard is used. Four recent large studies determined the sensitivity of urine LCR to be 86-96%.“,7,2”,24 In two of these studies, LCR and cell culture were directly compared, and LCR demonstrated significantly greater sensitivity: 94% versus 65%,” and 86% versus ~4%.~ One of these studies was a multicenter trial with a total prevalence of chlamydia of 8% (range: S--20% across centers). In this study, the positive predictive value of LCR was 99.3% and the negative predictive value was 99.4%.“i Ligase chain reaction may have the highest sensitivity available, but it is still less than 100%. False negative results could stem from urine not being contaminated with cervical organisms, DNA mutation, and loss of the target plasmid by the 166

organism. Ligase chain reaction inhibitors exist but they have less effect than PCR inhibitors. Preliminary evidence estimates the prevalence of LCR inhibitors to be 5-6% of all specimens.‘,7 Ligase chain reaction is available commercially for detection of N gonorrhoeae in endocervical and urine specimens. Preliminary evaluations have shown reasonable accuracy of the test for both media. The assay amplifies target DNA sequences within the N gonorrhoeae opacity gene. It is designed to offer the same relative advantages as other amplification methods, such as rapidity and elimination of the logistical problems that can decrease test sensitivity. Performance evaluations to date have been conducted primarily in high prevalence populations using expanded gold standards.1”,‘4 A recent multicenter study, in which the prevalence of genital gonorrhea ranged from 3-18% and the total prevalence was 7%) compared LCR on endocervical swabs to culture. The sensitivity of LCR across centers was 96-lOO%, compared to 73-92% for culture. LCR sensitivity remained fairly high at 96% at the

chain

reaction:

LCR. ligase

chain

reaction

center with the lowest prevalence, whereas the sensitivity of culture was 73% at the center with the 3% prevalence.14 Another study performed in a high prevalence population compared urine LCR to both endocervical culture and combined endocervical and urethral culture. The accuracy of all three methods was approximately equal, with sensitivities of 95-96% and specificities of loo%.‘” As with LCR testing for chlamydia, the advantages of LCR over culture for detection of gonorrhea are most pronounced in low prevalence screening populations, where the sensitivity appears to be greater and the logistics of LCR are better suited. One important advantage of gonorrhea culture over LCR, which chlamydia culture does not possess, is significantly lower cost. Although the relative costs of all the various tests differ from center to center, gonorrhea culture is typically one third the cost of PCR or LCR. Thus, LCR for gonorrhea likely will have narrower clinical applicability than LCR for chlamydia. In settings where the performance of pelvic examinations is difficult, or where transport conditions may Prim Care Update

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lead to reduced sensitivity of culture, urine LCR testing for gonorrhea has potential advantages. Examples of such settings include school based clinics, detention centers, or other institutional infirmaries.‘” Endocervical specimens for LCR testing do not offer any advantages over urine specimens.

Summary Ultimately, the choice of methodologies used in a particular setting will be based on many factors. Pertinent characteristics of each test described in this article are surnmarized in Table 2. Until recently, culture has been accepted as the most accurate means of diagnosing infection with C fruchomatis or N gonorrhoeue. Advances in nucleic acid technologies have provided us with chlamydia and gonorrhea tests that may be more sensitive and just as specific as culture. with greater logistical efficiency. The costs of these newer methods are comparable to, or lower than, culture for chlamydia detection. In the case of gonorrhea, culture still offers a significant cost advantage. Because of its time-tested 1000/o specificity, culture will remain a mainstay for diagnosis of gonorrhea and chlamydia infection in cases with medicolegal implications. Culture is the only method available that has been adequately tested for specimens from sites other than the genitourinary tract .J The best diagnostic method for a particular setting will vary depending on one’s desire for accuracy, the cost of the test, logistical considerations, and the prevalence of infection within the population being served.

for the 3. CDC. Recommendations prevention and management of Chlamydia trachomatis infections. MMWR 1993;42(RR-12):7-8. 4. Woods G. Update on laboratory diagnosis of sexually transmitted diseases. Clin Lab Med 1995;15:66584.

5. Iwen PC, Walker RA, Warren KL, et al. Evaluation of nucleic acid-based test (PACE 2C) for simultaneous detection of Chlamydia trachomatis and N gonorrhoeae in endocervital specimens. J Clin Microbial 1995:33:2587-91. 6. Lee HH, Chernesky MA, Schachter J. et al. Diagnosis of Chlamvdia trachomatis genitourinary infection in women bv ligase chain reaction assay in u&e. Lancet 1995:345: 213-6. 7.

1411-4.

8. Pasternack R. Vuorinen P. Kukankorpi A, Pitk+irvi T, Miettinen A. Detection of Chlamydia trachomatis infections in women by Amplicor PCR: comparison of diagnostic performance with urine and cervical specimens. J Clin Microbial 1996;34:995-8. Y. . LeBar WD. Keeping up with new technology: new approaches to diagnosis of chlamydia infection. Clin Chem 1996;42:809-12. 10. Mahoney JB, Chernesky MA. Elect of swab type and storage temperature on the isolation of Chlamydia trachomatis from clinical specimens. J Clin Microbial 1985:22: 865-7.

J, Vesterinen E. Chlamydia trachomatis in cervicitis and urethritis in women. Stand J Infect Dis 1982;32:45-54. 12. Stamm WE. Diagnosis of Chlamydia trachomatis genitourinary infections. Ann Intern Med 1988: 108:710-7. 13.

1.

42(SS-3):21-7.

Smith KR, Ching S. Lee H, et al. Evaluation of ligase chain for use with urine for identification Neisseria gonorrhoeae in females attending a sexually transmitted disease clinic. J Clin Microbial 1995; 33:455-7.

14.

Cbing S, Lee H, Hook EW III. Jacobs MR, Zenilman J. Ligase chain reaction for detection of Neisseria &Jon-

orrheae in urogenital swabs. J Clin Microbial 1995;33:3111-4. Hook EW III, Handenfield HH. Gonococcal infections in the adult. In: Holmes K, et al, editors. Sexually transmitted diseases. New York: McGraw-Hill Book Co, 1995:14965.

Meittinen A, Vuorinen P. Varis T, HBllstriim 0. Comparison of enzyme immunoassay antigen detection, nucleic acid hybridization and PCR assay in the diagnosis of Chlamydia trachomatis infection. Em J Clin Microbial Infect Dis 1995;14: 546-9. 17. Hadgu A. The discrepancy of discrepant analysis. Lancet 1996;348: 592-3. 18. Woods GL, Garza DM. Use of GenProbe probe competition assay for direct detection of Chlamydia trachomatis and N. gonorrhoeae in urogenital specimens. J Clin Microbiol 1994;32;2540-3. 19. Dille BJ, Butzen CC, Birkenmeyer LG. Amplification of Chlamydia trachomatis DNA by ligase chain reaction. J Clin Microbial 1993:31: 729-31. 20. Smith TF, Weed LA. Comparison oi urethral swabs, urine, and urinary sediment for isolation of Chlamydia trachomatis. J Clin Microbial 1975; 2:134-5. 21. Chernesky M, Castriciano S, Sellors J, et al. Detection of Chlamydia trachomatis antigens in urine as an alternative to swabs and cultures. J Infect Dis 1990;161:124-6. 22. Sellers JW, Mahony JB, Jang D, et al. Comparison of cervical, urethral, and urine specimens for detection of Chlamydiu trachomatis in women. J Infect Dis 1991:164: 16.

205-B. 23.

11. Paavonen

References CDC. Sexually transmitted diseases treatment guidelines. MMWR 1993; 42(RR14):50-62. 2. CDC. Special focus: surveillance for reproductive health. MMWR 1993;

Schachter J, Moncada J, Whidden R. et al. Noninvasive tests for diagnosis of Chlamydia trachomatis infection: application of ligase chain reaction to first catch urine specimens of women. J Infect Dis 1995;172:

15.

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Schachter J. Stamm WE, Quinn TC, et al. Ligase chain reaction to detect Chlamydia trachomatis infections of the cervix. J Clin Microbial 1994; 32:2540-3.

24.

Chernesky MA, Jang D, Lee H. et al. Diagnosis of Chlamydia trachomatis infections in men and women by testing first void urine by ligase chain reaction. J Clin Microbial 1994:32:2682-5.

Address correspondence and reprint requests to Gregoty J. Locksmith, MD, University of Florida College of Medicine. Department of Obstetrics and Gynecology, PO Box lOU294, Gainesville, FL 32610-029~.