Comparison of DNA-probe test and culture for the detection of Neisseria gonorrhoeae in genital samples

Nucleic acid amplification tests for gonorrhea and chlamydia: practice and applications

Nucleic acid amplification tests (NAATs), which are highly sensitive and specific, have provided the ability to use alternative sam-ple types for the diagnosis of sexually transmitted infections (STIs). Self-collected genital specimens, such as urine or even vaginal swabs, can now be accurately used to diagnose gonorrhea or chlamydia infections. In many cases, use of these sample types can decrease the necessity for a clinician to perform a pelvic examination on women or to collect a urethral swab from men, thus extending the diagnostic capability for detecting these infections to nonclinic screening venues. As most chlamydia infections and many gonorrhea infections are asymptomatic, the use of NAATs for self-collected samples greatly increases the types and numbers of patients that can be screened outside of clinic settings. Self-sampling also allows clinicians to easily screen patients in the clinic for STIs who are not presenting for pelvic or urogenital examinations. The application of NAATs to self-collected specimens has the potential to augment public health programs designed to control the epidemic of STIs in the community.

Urine nucleic acid amplification tests for the diagnosis of sexually transmitted infections in clinical practice

PURPOSE OF REVIEW

With the advent of highly sensitive and specific nucleic acid amplification assays, this report will demonstrate that self-collected genital specimens, such as urine or even vaginal swabs can be accurately used to diagnose sexually transmitted infections.

RECENT FINDINGS

Use of self collected samples can eliminate the necessity of a clinician to perform a pelvic examination for women or collect a urethral swab for men, thus extending the diagnostic capability for sexually transmitted infections to non-clinic screening venues. As many sexually transmitted infections are asymptomatic, this ability to use self-sampling greatly increases the numbers of patients that can be screened, and has the potential to augment public health programs designed to control the epidemic of sexually transmitted infections in the community. Patient collected samples are highly acceptable, highly accurate, and are becoming widely used. Self-sampling also allows clinicians to easily screen patients in the clinic, who are not presenting for pelvic or urogenital examinations, for sexually transmitted infections.

SUMMARY

Highly accurate molecular tests and easily obtained self-collected urogenital samples represent the ideal combination for obtaining the public health goal of decreasing the sexually transmitted infection epidemic among sexually active persons in the United States today.

Clinical management of chlamydia and gonorrhea infection in a county teaching emergency department--concerns in overtreatment, undertreatment, and follow-up treatment success

To date, several studies have examined overtreatment or undertreatment of Neisseria gonorrheae, Chlamydia trachomatis, or both in women. However, no study has looked at both subpopulations together, along with eventual treatment of disease-positive patients who were not empirically treated. This study is unique, for it looks at all of these subpopulations to assess overall efficacy of management of these diseases in women. A 1-year prospective, descriptive study was performed in a teaching county hospital Emergency Department (ED). There were 1260 women receiving a pelvic examination and routine GEN-PROBE testing for gonorrhea and chlamydia who were studied. The main outcome measures were the proportion of women disease positive and initially not treated (undertreated), the proportion of women disease negative who were initially treated (overtreated), as well as the follow-up treatment rate for those undertreated. Finally, the subpopulation of women disease positive and not empirically treated was examined in detail. Of 1260 GEN-PROBE-tested women, 81 (6.4%, 95% CI 1.1-11.7%) were disease positive and 31/81 (38.3%, 95% CI 21.2-55.4%) of these women were undertreated. Furthermore, 20/31 (64.5%, 95% CI 43.5-85.5%) women did not return for follow-up treatment. The billable health care dollars of routine GENPROBE testing per woman (n = 11/1260, 0.9%) returning for treatment as a result of the test was $4762.80 US dollars. Four hundred twenty-six (33.8%) of the 1260 women were empirically treated on the initial visit. Of these 426 initially treated women, 376 (88.3%, 95% CI 85.1-91.5%) were GEN-PROBE negative for disease (overtreated). The billable health care dollars of this overtreatment was $12,449.51 US dollars. This study demonstrates that health care providers are substantially overtreating women who are gonorrhea and chlamydia negative. This generates moral, ethical, health care, and financial concerns. Additionally, one-third of disease-positive women are not treated on initial visit and the majority of undertreated patients are not returning for subsequent treatment. This study provides support for investigating improved methods in the management of chlamydia and gonorrhea in women.

The Use of Urine and Self-obtained Vaginal Swabs for the Diagnosis of Sexually Transmitted Diseases

Studies have reported that self-collected specimens, such as urine or vaginal swabs, can be successfully used to diagnose sexually transmitted infections when they are used with nucleic acid amplification assays. This eliminates the necessity for a clinician-performed pelvic examination for women, or a urethral swab for men, for sample collection. These nucleic acid amplification assays used with self-collected specimens are highly sensitive and specific, and their use may be extended to broad nonclinic screening venues, where their use can augment public health programs designed to control the epidemic of sexually transmitted diseases.

Detection of Neisseria gonorrhoeae and Chlamydia trachomatis colonization of the gravid cervix

OBJECTIVES

The aims of the study were to determine whether a Gram stain of cervical mucus can accurately rule out infection with Neisseria gonorrhoeae or Chlamydia trachomatis and to compare a diagnostic test that is based on the polymerase chain reaction with a deoxyribonucleic acid probe in the detection of these organisms.

STUDY DESIGN

Gravid patients were screened for N gonorrhoeae and C trachomatis with a deoxyribonucleic acid probe, Gram stain, and analysis with the polymerase chain reaction. A normal, noninfected sample was defined by <10 polymorphonuclear leukocytes per high-power field on the Gram stain. Standard statistical methods were used to compare results of the Gram stain and the deoxyribonucleic acid probe, as well as to compare results of deoxyribonucleic acid probe hybridization and polymerase chain reaction analysis. A P value of <.05 was considered statistically significant.

RESULTS

Patient enrollment totaled 519. The prevalence of infection as determined by deoxyribonucleic acid probe hybridization was 1.4% for N gonorrhoeae (7/518) and 6.8% for C trachomatis (35/518). The cervical Gram stain predicted the absence of infection in 17% (90/518) of patients, with a negative predictive value of 99% for N gonorrhoeae and 97% for C trachomatis. African American race, age <20 years, and unmarried status were all predictors of the presence of C trachomatis or N gonorrhoeae cervicitis. For the patients who lacked these risk factors (n = 74), the Gram stain had 100% negative predictive value. Analysis with the polymerase chain reaction detected 8 additional patients with C trachomatis and 105 additional patients with N gonorrhoeae, in comparison with deoxyribonucleic acid probe hybridization.

CONCLUSION

The cervical Gram stain can accurately predict the absence of N gonorrhoeae and C trachomatis in gravid women. Analysis with the polymerase chain reaction indicates that N gonorrhoeae and C trachomatis are significantly more prevalent in this population than previously reported.

Evaluation of the abbott LCx assay for detection of Neisseria gonorrhoeae in endocervical swab specimens from females

The Abbott LCx Neisseria gonorrhoeae assay (Abbott Laboratories, Abbott Park, Ill.) uses a ligase chain reaction (LCR) amplification in the LCx probe system for detection of a specific nucleotide sequence in the Opa-encoding gene of N. gonorrhoeae. We evaluated the LCx assay in a comparison with conventional culture employing modified Thayer-Martin media for the detection of N. gonorrhoeae from female endocervical specimens obtained from patients attending a sexually transmitted disease clinic. Discordantly LCR-positive and culture-negative specimens were further evaluated by testing with another LCR assay which used an N. gonorrhoeae-specific pilin probe. Specimens positive by both LCR assays were considered confirmed LCx-positive specimens. A specimen was considered to contain N. gonorrhoeae when it was either culture positive or culture negative and confirmed LCx positive. A total of 403 female endocervical specimens were evaluated. The prevalence of N. gonorrhoeae in this population was 8.7%. The sensitivity and specificity of the LCx assay were 94.3 and 99.4%, and those of culture were 77.1 and 100%, respectively. The Abbott LCx assay is a rapid, sensitive method for detection of N. gonorrhoeae in female endocervical specimens.

Evaluation of the Gen-Probe PACE 2 assay for the detection of asymptomatic Chlamydia trachomatis and Neisseria gonorrhoeae infections in male arrestees

BACKGROUND

The LET and Gen-Probe PACE 2 assay are used to screen male arrestees for evidence of infection with chlamydia and gonorrhea in the intake/booking area of the Jefferson Parish Correctional Center.

GOAL OF THIS STUDY

To determine the accuracy of the Gen-Probe PACE 2 assay for the detection of asymptomatic infection with Chlamydia trachomatis and Neisseria gonorrhoeae infections in male arrestees.

STUDY DESIGN

From December 1993 to March 1994, 196 arrestees younger than 22 years were screened with the Gen-Probe PACE 2 assay and McCoy shell vial culture for Chlamydia trachomatis. From April to October 1994, 444 arrestees of all ages were screened with the Gen-Probe PACE 2 assay and standard culture for Neisseria gonorrhoeae. The sensitivity, specificity, and predictive values of the Gen-Probe PACE 2 assay, compared with culture, were calculated with 95% confidence intervals.

RESULTS

The Gen-Probe PACE 2 assay compared with culture had a sensitivity, specificity, and positive predictive value for Chlamydia trachomatis of 84%, 99%, and 93% and for Neisseria gonorrhoeae of 54%, 99.5%, and 78%.

CONCLUSION

The Gen-Probe PACE 2 assay is useful for screening young males in this jail setting and is more accurate for detecting Chlamydia trachomatis compared with Neisseria gonorrhoeae.

Comparisons of cost and accuracy of DNA probe test and culture for the detection of Neisseria gonorrhoeae in patients attending public sexually transmitted disease clinics in Los Angeles County

BACKGROUND

Strict handling and transport requirements for the successful use of culture in the detection of Neisseria gonorrhoeae warrant investigation of accurate and cost-effective test alternatives such as the Gen-Probe PACE 2 DNA probe assay (Gen-Probe, Inc., San Diego, CA).

STUDY DESIGN

The Gen-Probe PACE 2 DNA probe assay for N. gonorrhoeae was compared with conventional culture methods in the principal Los Angeles County (LAC) Department of Health Services (DHS) Public Health Laboratory and three of its branch laboratories. Urethral and endocervical samples were collected from 1,566 patients (921 males; 645 females) attending six LAC DHS sexually transmitted disease clinics. Cost analysis was performed comparing material and labor costs of the two test methods.

RESULTS

The overall prevalence based on culture was 11.8% (15.7% for males; 6.4% for females). Nine samples were culture positive, Gen-Probe negative and four samples were culture negative, Gen-Probe positive and remained discordant after discrepant analysis. The sensitivity and specificity were 94.6% and 99.7%, respectively, for the PACE 2 assay compared with culture. The positive and negative predictive values were 97.8% and 99.3%, respectively. No statistically significant difference was found between the two tests. A cost analysis found an average cost of $3.11/test for culture and $3.85/test for PACE 2, given the approximate 12% disease prevalence in this population.

CONCLUSIONS

Gen-Probe's PACE 2 assay may provide an acceptable, cost-effective alternative to culture, especially among high-risk males.

Non-cultural detection of rectal and pharyngeal gonorrhoea by the Gen-Probe PACE 2 assay

OBJECTIVE

To assess the sensitivity and specificity of the Gen-Probe PACE 2 assay, which uses a chemiluminescent labelled single-stranded DNA probe to detect gonococcal ribosomal RNA (rRNA), for the non-cultural detection of rectal and pharyngeal gonorrhoea in homosexual men.

SUBJECTS

161 homosexual men attending the Department of Genitourinary Medicine, Edinburgh Royal Infirmary during the latter half of 1995 and the first quarter of 1996.

METHODS

Duplicate rectal and pharyngeal swabs were collected for culture on modified New York City (MNYC) medium and detection of gonococcal nucleic acid by the Gen-Probe assay. Repeatedly reactive Gen-Probe specimens from culture negative patients were also tested by the Gen-Probe competition assay (PCA).

RESULTS

Of the 161 patients, 23 (14.3%) gave a positive culture at one or both sites (rectum 10, throat 8, rectum and throat 5) compared with 28 (16.7%) who gave a positive Gen-Probe result at one or both sites (rectum 9, throat 11, rectum and throat 8). After resolution of discrepant results by PCA the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of Gen-Probe was 94.1%, 100%, 100% and 99.3% for rectal specimens while the corresponding values for pharyngeal specimens were 86.4%, 100%, 100%, and 97.9%. The sensitivity and NPV of rectal culture were 88.2% and 98.6% while the corresponding values for pharyngeal culture were 59% and 93.9%. Gen-Probe was significantly more sensitive than throat culture (p < 0.05) but not rectal culture (p > 0.2). The average Relative Light Units (RLU) value for the cut-off was 386 (range 351-450) while the average for a positive result was 20306 (range 403-110104): this was, however, significantly higher (p = 0.019) in rectal specimens 31325 (range 1705-110104) than in throat specimens 10447 (range 403-15633).

CONCLUSIONS

Gen-Probe PACE 2 assay is a sensitive and specific method for the detection of rectal and pharyngeal gonorrhoea. As the Gen-Probe assay may detect nucleic acid from non viable gonococci the clinical significance of a probe positive culture negative specimen from a patient without culture evidence of gonorrhoea at another site is uncertain and requires further consideration. Nevertheless a positive result does indicate exposure to infection and could be important in ensuring appropriate partner notification action. If non-cultural methods are used to screen for gonococcal infection cultures should be obtained from patients with positive results in order that the antibiotic susceptibility and molecular epidemiology of the gonococcal population can be monitored.

Neisseria gonorrhoeae RNA/DNA hybridization and culture for screening of gonococcal infections in a low-prevalence population

Gonorrhea is still a major sexually transmitted disease (STD) worldwide. Its etiologic diagnosis is based on identification of the causative agent, Neisseria gonorrhoeae, by culture of genital secretions, which is often hampered by difficulties of sample collection and transport. Alternatively, nucleic acid hybridization techniques for routine diagnosis of N. gonorrhoeae appear to be useful by eliminating problems associated with bacterial viability, particularly for surveillance of low-prevalence populations. Our study among 1,508 outpatients undergoing routine examination for common STDs used RNA/DNA hybridization with a DNA probe specific for N. gonorrhoeae (Gen Probe Pace 2) and classical culture. Of the 1,750 specimens tested, 12 were positive by DNA probe and culture. In 8 cases, only DNA probe was positive while culture was negative. In 3 of these discrepant cases clinical and epidemiological data suggested true N. gonorrhoeae infection. Thus, DNA probe assay for N. gonorrhoeae may greatly improve screening of N. gonorrhoeae among low-prevalence populations. However, culture remains mandatory for testing antimicrobial resistance of these highly communicable infectious agents.

A tale of two sexually transmitted diseases. Prevalences and predictors of chlamydia and gonorrhea in women attending Colorado family planning clinics

BACKGROUND

The comparative prevalences and predictors of chlamydia and gonorrhea have not been studied in the family planning clinic population.

GOALS

To determine the comparative prevalences and predictors of chlamydia and gonorrhea among Colorado family planning clinic patients.

STUDY DESIGN

Cross-sectional study of public and private family planning clinic patients in Colorado tested for both chlamydia and gonorrhea (n = 12,926).

RESULTS

Among women tested for both infections, the chlamydia prevalence rate was 4.5% and the gonorrhea prevalence rate was 0.5%. Multivariate analysis showed that independent predictors of chlamydia were age younger than 25 years, black or Hispanic race-ethnicity, cervical friability, mucopus, exposure to a sex partner with chlamydia, or multiple recent sex partners. Independent predictors of gonorrhea were age younger than 20 years, black or Hispanic race-ethnicity, or exposure to a sex partner with gonorrhea; adjusted odds ratios for exposure to gonorrhea and black race were the highest for either infection.

CONCLUSIONS

The gonorrhea prevalence rate was very low compared to that of chlamydia in patients at Colorado family planning clinics. Cost-effective gonorrhea testing strategies are needed for this population.

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

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

The evaluation of infection and pulmonary maturity in women with premature rupture of the membranes

Although the etiology of PROM is multifactorial, increasing evidence regarding clinical risk factors, membrane histology, membrane culture, and amniotic fluid microbiology shows a strong association with infection. Recent studies suggest an association between genital tract infection, preterm labor (PTL), and preterm premature rupture of the membranes (pPROM). If correct, this information may be used to target areas for prevention, as well as to develop management protocols. This article reviews both the diagnostic tests for the causes associated with pPROM and the evaluation of intraamniotic infection and pulmonary maturity in patients with pPROM.

Laboratory diagnosis of sexually transmitted diseases in facilities within the United States. Results of a national survey

BACKGROUND AND OBJECTIVES

The diagnosis of many sexually transmitted diseases (STD) requires laboratory testing. The authors assessed the effects of the introduction of new tests and regulations on STD testing.

STUDY DESIGN

A questionnaire survey was mailed to a random sample of facilities listed in the STD Referral Database inquiring about tests offered, changes in testing, and reasons for changes.

RESULTS

Responses from 405 facilities were analyzed. Most responding facilities collected specimens for nontreponemal tests for syphilis (352 of 405 [86.9%]). Since each facility's information was last updated, the number reporting testing for Chlamydia trachomatis rose from 160 of 405 (39.5%) to 288 of 405 (71.1%), but testing for gonorrhea and chancroid decreased (365 of 405 [90.1%] to 328 of 405 [81%], and 182 of 405 [44.9%] to 32 of 405 [7.9%], respectively). Of 364 responses to a question on changes in tests performed in the last 2 years, 249 (68.4%) reported no change, 81 (22.3%) reported an increase, and 37 (10.2%) reported a decrease. The most frequently added tests were nonculture tests for C. trachomatis (34 of 81 [42%]) and the most frequent reason for adding tests was targeted funding (25 of 81 [30.9%]). The most frequently discontinued tests were cultures and gram stains for gonorrhea (15 of 37 [40.5%]) and other in-house tests (9 of 37 [24.3%]). Most facilities that discontinued testing cited the Clinical Laboratory Improvement Act as the reason (34 of 37 [91.9%]; 95% confidence interval = 78.1%, 98.3%).

CONCLUSIONS

The number of facilities testing for C. trachomatis has increased with funding and with the availability of nonculture tests, but the number of those testing for chancroid and gonorrhea has decreased. Implementation of the Clinical Laboratory Improvement Act may be associated with a decrease in the number of facilities performing tests for STD.

Comparison of DNA probe (Gen-Probe) with culture for the detection of Neisseria gonorrhoeae in an urban STD programme

BACKGROUND AND OBJECTIVES

The DNA probe assay is an alternative to culture for the detection of Neisseria gonorrhoeae which does not depend on the viability of the organism. There have been few published studies comparing the two methodologies. The majority of these studies have shown the probe assay to be comparable to culture. The goal of this study was to compare the performance of the DNA probe assay with culture in a high prevalence setting with nearly optimal culture transport conditions.

METHODS

Genital specimens for culture and for DNA probe assay were collected at the time of the routine visit for STD clinic patients. Results of the two methods were compared. Discrepant results were further analysed using the results of direct patient Gram stains.

RESULTS

Satisfactory matched specimens were available for 999 patients. The overall sensitivity and specificity of the DNA probe as compared with culture was 90 and 96%. Resolved values achieved by factoring in the results of direct patient Gram stains did not significantly improve the performance of the probe.

CONCLUSION

Culture remains the test of choice for the detection of gonorrhoea in a high prevalence setting where culture transport conditions are adequate.

Evaluation of nucleic acid-based test (PACE 2C) for simultaneous detection of Chlamydia trachomatis and Neisseria gonorrhoeae in endocervical specimens

A nucleic acid-based test (Gen-Probe PACE 2C System) was evaluated for the ability to detect Chlamydia trachomatis and Neisseria gonorrhoeae from endocervical specimens in a single assay. Three swab samples, randomized for collection order, were obtained from each patient and tested by N. gonorrhoeae and C. trachomatis culture and by the PACE 2C probe assay. Fifty of 395 specimens were culture positive for N. gonorrhoeae (17 specimens), C. trachomatis (26 specimens), or both (7 specimens), of which PACE 2C testing detected 48 specimens. The PACE 2C assay was positive for 56 specimens, including 8 specimens not positive by culture. Of the total of 10 discrepancies between culture and PACE 2C results, resolution testing yielded four false-negative culture, four false-positive PACE 2C, and two false-negative PACE 2C results. The sensitivity, specificity, and positive and negative predictive values for PACE 2C after reevaluation were 96.3, 98.8, 92.9 and 99.4%, respectively. The overall sensitivities for C. trachomatis and N. gonorrhoeae culture were 89.2 and 88.9%, respectively. The prevalence rate for C. trachomatis was 9.4%, and that for N. gonorrhoeae was 6.8%. The Gen-Probe PACE 2C System is a reliable alternative for screening endocervical specimens for both C. trachomatis and N. gonorrhoeae in a single assay.