Confirmation by 16S rRNA PCR of the COBAS AMPLICOR CT/NG test for diagnosis of Neisseria gonorrhoeae infection in a low-prevalence population

Targeted surveillance strategies for efficient detection of novel antibiotic resistance variants

Genotype-based diagnostics for antibiotic resistance represent a promising alternative to empiric therapy, reducing inappropriate antibiotic use. However, because such assays infer resistance based on known genetic markers, their utility will wane with the emergence of novel resistance. Maintenance of these diagnostics will therefore require surveillance to ensure early detection of novel resistance variants, but efficient strategies to do so remain undefined. We evaluate the efficiency of targeted sampling approaches informed by patient and pathogen characteristics in detecting antibiotic resistance and diagnostic escape variants in Neisseria gonorrhoeae, a pathogen associated with a high burden of disease and antibiotic resistance and the development of genotype-based diagnostics. We show that patient characteristic-informed sampling is not a reliable strategy for efficient variant detection. In contrast, sampling informed by pathogen characteristics, such as genomic diversity and genomic background, is significantly more efficient than random sampling in identifying genetic variants associated with resistance and diagnostic escape.

Prevalence and sociodemographic risk factors of chlamydia, gonorrhoea and syphilis: a national multicentre STI survey in New Caledonia, 2012

OBJECTIVES

To estimate prevalence and identify sociodemographic risk factors for Neisseria gonorrhoeae (NG), Chlamydia trachomatis (CT) and Treponema pallidum infections in New Caledonia.

METHOD

A national cross-sectional survey was undertaken using a three-stage random sampling of general practice surgeries and public dispensaries. Participants were included through opportunistic screening and using a systematic step for selection. The study sample was weighted to the general population aged 18-49 years. Prevalence and risk factors were calculated by logistic regression.

RESULTS

CT was the most common sexually transmitted infection, with a prevalence of 9% (95% CI 6.6% to %11.4), followed by NG 3.5% (95% CI 1.9% to 5.1%), previous or latent syphilis 3% (95% CI 1.7% to 4.3%), NG and CT co-infection 2.1% (95% CI 0.8% to 3.3%) and active syphilis 0.4% (95% CI 0.0% to 0.9%). Being from a young age group (18-25 years), being single, having a low level of education and province of residence were all associated with higher prevalence of all three STIs. Being of Melanesian origin was associated with higher prevalence of both CT and NG. There was a significant interaction between ethnic group and province of residence for prevalence of CT. Female gender was associated with higher prevalence of CT.

CONCLUSIONS

The prevalence of CT was similar to estimates from other healthcare-based surveys from the Pacific, but higher for NG and lower for active syphilis infection. All sexually transmitted infections estimates were much higher than those found in population-based surveys from Europe and the USA. The sociodemographic risk factors identified in this study will help guide targeted prevention and control strategies in New Caledonia.

Evaluation of six commercial nucleic acid amplification tests for detection of Neisseria gonorrhoeae and other Neisseria species

Molecular detection of Neisseria gonorrhoeae in extragenital samples may result in false-positive results due to cross-reaction with commensal Neisseria species or Neisseria meningitidis. This study examined 450 characterized clinical culture isolates, comprising 216 N. gonorrhoeae isolates and 234 isolates of nongonococcal Neisseria species (n = 218) and 16 isolates of other closely related bacteria, with six commercial nucleic acid amplification tests (NAATs). The six NAATs tested were Gen-Probe APTIMA COMBO 2 and APTIMA GC, Roche COBAS Amplicor CT/NG and COBAS 4800 CT/NG tests, BD ProbeTec GC Qx amplified DNA assay, and Abbott RealTime CT/NG test. All assays except COBAS Amplicor CT/NG test where four (1.9%) isolates were not detected showed a positive result with all N. gonorrhoeae isolates (n = 216). Among the 234 nongonococcal isolates examined, initial results from all assays displayed some false-positive results due to cross-reactions. Specifically, the COBAS Amplicor and ProbeTec tests showed the highest number of false-positive results, detecting 33 (14.1%) and 26 (11%) nongonococcal Neisseria isolates, respectively. On the first testing, APTIMA COMBO 2, APTIMA GC, Abbott RealTime, and Roche COBAS 4800 showed lower level of cross-reactions with five (2.1%), four (1.7%), two (1%), and two (1%) of the isolates showing low-level positivity, respectively. Upon retesting of these nine nongonococcal isolates using freshly cultured colonies, none were positive by the APTIMA COMBO 2, Abbott RealTime, or COBAS 4800 test. In conclusion, the COBAS Amplicor and ProbeTec tests displayed high number of false-positive results, while the remaining NAATs showed only sporadic low-level false-positive results. Supplementary testing for confirmation of N. gonorrhoeae NAATs remains recommended with all samples tested, in particular those from extragenital sites.

Aptima Combo 2 testing detected additional cases of Neisseria gonorrhoeae infection in men and women in community settings

Aptima Combo 2 (AC2) Neisseria gonorrhoeae testing of 81,405 patients who were tested by culture and 14,666 who were AC2 tested for Chlamydia trachomatis detected 142 extra infections and confirmed 106 culture-positive samples (the positivity rate increased from 0.13 in testing by culture to 0.26 in testing by AC2). Retrievable AC2 positive samples were confirmed (98.5%) by an alternate AGC test.

Nucleic Acid Amplification of the opa Gene for Detection of Neisseria gonorrhoeae: experience from a diagnostic laboratory

We report results of Neisseria gonorrhoeae nucleic acid amplification testing (NAAT) with the Abbott m2000 PCR at a tertiary laboratory 6 months after its introduction. Of 5,475 specimens tested, 45 samples (0.82%) tested positive for N. gonorrhoeae. Eight were not cultured, but seven tested positive with a porA pseudogene NAAT.

Design of a multiplex PCR assay for the simultaneous detection and confirmation of Neisseria gonorrhoeae

OBJECTIVES

To improve the detection of Neisseria gonorrhoeae by designing a multiplex PCR assay using two N gonorrhoeae-specific genes as targets, thereby providing detection and confirmation of a positive result simultaneously.

METHODS

PCR primers were designed to detect two N gonorrhoeae genes, namely porA and pgi1. Primers for an internal control targeting the ompW gene of Vibrio cholerae were also designed and incorporated in the assay. The DNA of 45 clinical isolates including 33 N gonorrhoeae isolates, seven non-gonococcal Neisseria species, and five non-Neisseria species was tested using the multiplex PCR assay.

RESULTS

All 33 N gonorrhoeae isolates were successfully detected by the assay and none of the non-gonococcal isolates was detected. The assay showed a sensitivity and specificity of 100%, and a limit of detection of 1.25 ng of DNA.

CONCLUSION

This multiplex PCR assay offers a sensitive and specific assay suitable for the detection of N gonorrhoeae, and offers real potential for diagnostic use.

Diagnosis, management and prevalence estimation of gonorrhoea: influences of Aptima Combo 2 assay with alternative target confirmation

Case-notes and laboratory data were retrospectively reviewed for influences of dual testing by Aptima Combo 2 (AC2) for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) on the diagnosis, management and prevalence estimation of gonorrhoea in the genitourinary (GU) medicine clinic and community. NG positives by AC2 were confirmed by Aptima Gonococcus assay. Unconfirmed positives were rare. Our study showed that in the GU medicine clinic, AC2 detected about 20% extra cases of NG beyond culture. For best standard of care, NG culture and microscopy are still required in some patients to ensure that treatment is rapid and appropriate. Compared to self-referral at the GU medicine clinic, community tests made a substantial contribution to the overall number of NG cases found (40 community versus 35 Macclesfield GU medicine clinic). The ratio of female to male NG cases found was significantly higher (P = 0.002) in the community (13 M, 27 F) than at the GU medicine clinic (25 M, 10 F). In the community, over 60% of NG infections occurred in chlamydia-negative patients. The overall prevalence of NG in the GU medicine clinic was 1.3%, the true prevalence being much lower at 0.9% on primary test. Prevalence in the community was 0.4%. Data from dual testing in the community can clarify NG prevalence beyond the existing KC60 (sexually transmitted infections) reports.

Performance of three nucleic acid amplification tests for detection of Chlamydia trachomatis and Neisseria gonorrhoeae by use of self-collected vaginal swabs obtained via an Internet-based screening program

Use of self-obtained vaginal specimens processed by nucleic acid amplification tests (NAATs) has significantly increased the utilization of nontraditional locations for Chlamydia trachomatis and Neisseria gonorrhoeae screening programs. One important emerging source of such venues includes home-based self-sampling kits available via the Internet. The objective of our study was to evaluate the performance of three commercially available NAATs (Becton-Dickinson ProbeTec SDA, Gen-Probe Aptima Combo2 TMA, and Roche Amplicor PCR) for detection of C. trachomatis and N. gonorrhoeae in vaginal samples obtained via an Internet-based screening program. From July 2004 to August 2005, 500 self-collected vaginal swabs were tested for C. trachomatis and N. gonorrhoeae by using all three NAATs. Another 500 samples were collected between August 2005 and November 2007 and tested by ProbeTec and Combo2; PCR testing was discontinued due to low specificity for N. gonorrhoeae. All tests were conducted according to the manufacturers' procedures; the "gold standard" for an infected C. trachomatis or N. gonorrhoeae patient was defined as > or = 2 positive NAAT results. Of the first 500 swabs submitted, 46 were C. trachomatis infected (9.2%) and 5 were N. gonorrhoeae infected (1.0%), and 3 of these were coinfected (0.6%). All C. trachomatis and N. gonorrhoeae Combo2-positive/ProbeTec-negative samples were confirmed as true positives by an alternative NAAT. For C. trachomatis, ProbeTec, Combo2, and PCR had sensitivities of 82.6%, 100%, and 100%, with specificities of 100%, 100%, and 99.3%, respectively. For N. gonorrhoeae, ProbeTec, Combo2, and PCR had sensitivities of 80%, 100%, and 100%, with specificities of 100%, 100%, and 98.8%, respectively. Of the total 1,000 swabs submitted, 92 were C. trachomatis infected (9.2%) and 15 were N. gonorrhoeae infected (1.5%), and 7 of these were coinfected (0.7%). There were no ProbeTec-positive/Combo2-negative samples. For C. trachomatis, ProbeTec and Combo2 had sensitivities of 81.5% and 100%, with specificities of 100% and 100%, respectively. For N. gonorrhoeae, ProbeTec and Combo2 had sensitivities of 80% and 100%, with specificities of 100% and 100%, respectively. Overall, ProbeTec had 17 C. trachomatis false-negative results (1.7%) and 3 N. gonorrhoeae false-negative results (0.3%), while Combo2 had none. Our results were consistent with the sensitivities and specificities stated by the manufacturers. NAATs perform well for detection of chlamydia and gonorrhea with self-obtained vaginal swabs shipped in a dry state to a laboratory. For 1,000 self-collected vaginal swabs tested by NAATs, the sensitivities for C. trachomatis and N. gonorrhoeae for Combo2 were 100% and 100%, while they were 81.5% and 80%, respectively, for ProbeTec. For 500 PCR samples, the C. trachomatis sensitivity was 100% and the N. gonorrhoeae sensitivity was 100%, with specificities of 99.3% and 98.8%, respectively.

Evaluation of CDC-recommended approaches for confirmatory testing of positive Neisseria gonorrhoeae nucleic acid amplification test results

We evaluated three of the CDC approaches for confirming Neisseria gonorrhoeae (gonococcus [GC])-positive nucleic acid amplification test (NAAT) results: (i) repeating the original test on the original specimen, (ii) testing the original specimen with a different test, and (iii) performing a different test on a duplicate specimen collected at the same visit. For the first approach, clinical specimens were initially tested by Aptima Combo 2 (AC2) (Gen-Probe Inc., San Diego, CA), ProbeTec (strand displacement amplification [SDA]) (Becton Dickinson Co., Sparks, MD), and Amplicor (PCR) (Roche Molecular Systems, Branchburg, NJ). The original GC-positive specimens were then retested by the same NAAT for confirmation. For the second approach, specimens initially positive by AC2, SDA, or PCR were retested by different NAATs (SDA, PCR, AC2, and Aptima Neisseria gonorrhoeae assay [AGC]; Gen-Probe Inc.). For the third approach, duplicate urethral swabs and first-catch urine (FCU) samples from men and duplicate cervical swabs and FCU samples from women were each tested by SDA, AC2, and AGC in parallel. We found that 89 to 96% of samples positive by SDA, PCR, and AC2 were confirmed by repeat testing and that 85 to 98% of SDA, PCR, and AC2 results were confirmed by using different NAATs on the original specimen. For FCU samples from men, any NAAT can be used for confirmation. However, for all other specimen types, some NAATs cannot be used to confirm positive results from other NAATs. Thus, a single repeat test appears to be a reliable method for confirmation, but by doing more extensive testing, an additional 5% were confirmed. With >90% of all GC-positive NAATs being confirmed, our results show that confirmatory testing is not warranted for these genital specimens.

Biologie moléculaire et microbiologie clinique en 2007

La biologie moléculaire est omniprésente en biologie médicale et plus particulièrement en microbiologie. De nombreux articles démontrent son importance tant dans le domaine du diagnostic que du pronostic, de l'évaluation thérapeutique, de l'épidémiologie ou des risques biologiques naturels ou non. La quantité considérable d'articles sur ce sujet n'apporte pas toujours une réponse évidente sur le rôle de la biologie moléculaire dans un laboratoire de microbiologie qu'il soit hospitalier ou non. Cette revue constitue une synthèse des apports de cette discipline en microbiologie. À partir de cet état des lieux, certaines questions se posent, par exemple : la biologie moléculaire constitue-t-elle un réel apport en microbiologie ? Dans quelles indications prescrire un examen de biologie moléculaire ? Les réponses ne sont pas toujours simples. Elles sont évidentes dans certains cas (l'hépatite C par exemple) et le sont moins dans d'autres, la tuberculose par exemple. Dans la première partie de l'article, nous avons parlé des généralités appliquées à la microbiologie. Dans cette deuxième partie, nous abordons certaines applications, reflets de l'importance prise par la biologie moléculaire en microbiologie.

Evaluation of a rapid point-of-care test for the detection of gonococcal infection among female sex workers in Benin

OBJECTIVES

To assess the validity of the PATH (Seattle, Washington, USA) GC-Check rapid test, a point-of-care immunochromatographic strip test, in the detection of gonococcal infection among female sex workers (FSWs) in Benin.

METHODS

Women consulting consecutively at two FSW-dedicated clinics in Cotonou and Porto Novo (Benin) were recruited over three, 1-month periods between October 2003 and July 2004. After written informed consent, participants were administered a short interview and underwent a speculum examination where two cervical swabs were collected (in a subset of women, a vaginal swab was also collected). One cervical swab and the vaginal swab were immediately tested with the rapid test. The other cervical swab was frozen at -20 degrees C for at most four weeks and then transported to Québec (Canada), where it was tested with the Roche Amplicor CT/NG PCR assay. Samples positive for gonococcal infection were confirmed using a 16SrRNA PCR assay.

RESULTS

1084 FSWs (median age 29 years) participated in the study, of whom 50 (4.6%) had a confirmed gonococcal infection. The sensitivity, specificity, positive and negative predictive values of the rapid test on cervical samples were 70.0% (95% confidence interval (CI) 55.4% to 82.1%), 97.2% (95% CI 96.0% to 98.1%), 54.7% and 98.5%, respectively. The sensitivity of the rapid test on vaginal swabs among 759 women (37 positives for gonococcal infection) was significantly lower than with the cervical swab (54.1%, p = 0.008), whereas the specificity was comparable (98.2%, p = 0.13).

CONCLUSIONS

The PATH GC-Check test may be as efficient as a gold standard polymerase chain reaction (PCR) test for treating gonococcal infection when taking into account the proportion of women who do not return for their test results. In clinics serving populations with moderate prevalence of this infection, it could significantly reduce over-treatment compared to the syndromic approach.

Neisseria species identification assay for the confirmation of Neisseria gonorrhoeae-positive results of the COBAS Amplicor PCR

Screening assays for Neisseria gonorrhoeae exhibit low positive predictive values, particularly in low-prevalence populations. A new real-time PCR assay that detects and identifies individual Neisseria spp. using melt curve analysis was compared to two previously published supplementary assays. NsppID, a 16S rRNA real-time PCR/melt curve assay developed to distinguish N. gonorrhoeae from other Neisseria spp., was compared to real-time PCR assays targeting genes reportedly specific for N. gonorrhoeae, the cppB gene and the porA pseudogene. A total of 408 clinical specimens (324 female endocervical swabs and 84 male urine or urogenital swab specimens) were screened using the COBAS Amplicor assay for Chlamydia trachomatis and N. gonorrhoeae (CT/NG) (Roche Diagnostics, Indianapolis, IN) followed by confirmatory testing via real-time PCR. The NsppID assay detected Neisseria spp. in 150/181 COBAS-positive specimens (82%), including six dual infections, and identified N. gonorrhoeae in 102 (56%) specimens. Sixty-nine of 181 (38%) specimens were positive for N. gonorrhoeae by porA pseudogene, and 115/181 (64%) were positive for cppB. However, cppB was also positive in 15% of COBAS-negative specimens, more than either NsppID (4%) or porA pseudogene (2%) assays. The porA pseudogene assay had the highest specificity for both genders but the lowest sensitivity, especially in female specimens. NsppID had a slightly lower specificity but greater sensitivity and overall accuracy. The least desirable confirmatory assay was cppB, due to poor specificity. The NsppID assay is an accurate confirmatory assay for N. gonorrhoeae detection. In addition, the NsppID assay can identify the non-N. gonorrhoeae species responsible for the majority of false-positive results from the COBAS Amplicor CT/NG assay.

Pyrosequencing of the DNA gyrase gene in Neisseria species: effective indicator of ciprofloxacin resistance in Neisseria gonorrhoeae

The quinolone resistance determining region (QRDR) of the gyrA gene in ciprofloxacin-susceptible strains (n=53) and strains of Neisseria spp. with reduced susceptibility (n=70) was determined by the pyrosequencing method. Results showed that the QRDR of the gyrA gene is an effective molecular indicator of resistance to ciprofloxacin in Neisseria gonorrhoeae, and presumably in Neisseria meningitidis, but not in all other Neisseria spp. This sequence was not unique for N. gonorrhoeae and seems unsuitable for species verification of N. gonorrhoeae. However, whether it is also possible to use this region for verification depends on the specificity of the primary screening method used.

A fast real-time polymerase chain reaction method for sensitive and specific detection of the Neisseria gonorrhoeae porA pseudogene

Ever since the advent of molecular methods, the diagnostics of Neisseria gonorrhoeae has been troubled by false negative and false positive results compared with culture. Commensal Neisseria species and Neisseria meningitidis are closely related to N. gonorrhoeae and may cross-react when using molecular tests comprising too-low specificity. We have devised a real-time polymerase chain reaction (PCR), including an internal amplification control, that targets the N. gonorrhoeae porA pseudogene. DNA was automatically isolated on a BioRobot M48. Our subsequent PCR method amplified all of the different N. gonorrhoeae international reference strains (n = 34) and N. gonorrhoeae clinical isolates (n = 176) but not isolates of the 13 different nongonococcal Neisseria species (n = 68) that we tested. Furthermore, a panel of gram-negative bacterial (n = 18), gram-positive bacterial (n = 23), fungal (n = 1), and viral (n = 4) as well as human DNA did not amplify. The limit of detection was determined to be less than 7.5 genome equivalents/PCR reaction. In conclusion, the N. gonorrhoeae porA pseudogene real-time PCR developed in the present study is highly sensitive, specific, robust, rapid and reproducible, making it suitable for diagnosis of N. gonorrhoeae infection.

Why do we need quality-assured diagnostic tests for sexually transmitted infections?

The bacterial sexually transmitted infections (STIs) syphilis, gonorrhoea and chlamydia can all be cured with a single dose of antibiotic. Unfortunately, however, these infections often remain undiagnosed as many infected individuals have few if any symptoms. Diagnostic tests with high sensitivity and specificity are available for all three infections but, owing to their expense and the lack of laboratory capacity, most people in developing countries do not have access to these tests. There is a great need for simple, cheap diagnostic tests for STIs that can be performed at the point of care, enabling treatment to be given immediately. It is hoped that recent advances in our understanding of the pathogenesis of these infections, and the availability of the complete genome sequences for each causative organism, will lead to the development of improved point-of-care tests that will reduce the burden of these diseases in developing countries.

Why do we need quality-assured diagnostic tests for sexually transmitted infections?

The bacterial sexually transmitted infections (STIs) syphilis, gonorrhoea and chlamydia can all be cured with a single dose of antibiotic. Unfortunately, however, these infections often remain undiagnosed as many infected individuals have few if any symptoms. Diagnostic tests with high sensitivity and specificity are available for all three infections but, owing to their expense and the lack of laboratory capacity, most people in developing countries do not have access to these tests. There is a great need for simple, cheap diagnostic tests for STIs that can be performed at the point of care, enabling treatment to be given immediately. It is hoped that recent advances in our understanding of the pathogenesis of these infections, and the availability of the complete genome sequences for each causative organism, will lead to the development of improved point-of-care tests that will reduce the burden of these diseases in developing countries.

Use of a reliable PCR assay for the detection of Neisseria gonorrhoeae in Peruvian patients

Neisseria gonorrhoeae is the most common sexually transmitted disease-causing bacterium worldwide. An in-house PCR assay targeting the carbamoyl-phosphate synthase subunit A (carA) gene was developed for the specific detection of N. gonorrhoeae in clinical specimens. Samples from 605 patients were cultured on selective medium and assayed by PCR in a double-blind fashion. Of 605 urethral/cervical samples analysed, 13 were PCR-positive, of which 11 were culture-positive. The PCR showed a sensitivity and specificity of 100% and 99.7% with these samples. PCR targeting the carA gene appears to be a reliable method for the detection of N. gonorrhoeae in clinical specimens.

Nucleic acid amplification testing for Neisseria gonorrhoeae: an ongoing challenge

Nucleic acid amplification tests (NAATs) for the detection of Neisseria gonorrhoeae became available in the early 1990s. Although offering several advantages over traditional detection methods, N. gonorrhoeae NAATs do have some limitations. These include cost, risk of carryover contamination, inhibition, and inability to provide antibiotic resistance data. In addition, there are sequence-related limitations that are unique to N. gonorrhoeae NAATs. In particular, false-positive results are a major consideration. These primarily stem from the frequent horizontal genetic exchange occurring within the Neisseria genus, leading to commensal Neisseria species acquiring N. gonorrhoeae genes. Furthermore, some N. gonorrhoeae subtypes may lack specific sequences targeted by a particular NAAT. Therefore, NAAT false-negative results because of sequence variation may occur in some gonococcal populations. Overall, the N. gonorrhoeae species continues to present a considerable challenge for molecular diagnostics. The need to evaluate N. gonorrhoeae NAATs before their use in any new patient population and to educate physicians on the limitations of these tests is emphasized in this review.

Diagnostic Tests for Chlamydial and Gonorrheal Infections

Chlamydia trachomatis and Neisseria gonorrhoeae are the two most prevalent bacterial sexually transmitted infections reported in the United States. The purpose of this article is to review the various tests available for diagnosing C. trachomatis and N. gonorrhoeae. The nucleic acid amplification tests are preferred owing to their high sensitivity and specificity and use on specimens obtained noninvasively. Non-amplified non-culture tests, such as the DNA probe test, remain a choice for settings in which nucleic acid amplification tests are not available or affordable. Culture is recommended for use on conjunctival, oropharyngeal, and rectal specimens and in cases of suspected abuse. In addition, for gonorrhea, culture is recommended when screening in populations with a low prevalence of infection. Point-of-care tests are limited by low sensitivity and should be used for only populations unlikely to return for follow-up.

A real-time PCR assay for the detection of Neisseria gonorrhoeae in genital and extragenital specimens

A Neisseria gonorrhoeae LightCycler (NGpapLC) assay targeting the porA pseudogene was compared with bacterial culture for detection of N. gonorrhoeae in 636 clinical specimens (216 cervical, 185 urethral, 196 throat, and 39 rectal swab specimens). The specificity of the NGpapLC assay was further investigated by testing a bacterial reference panel comprising several Neisseria species. Overall, 19 (3.0%) specimens were positive and 613 (96.4%) specimens were negative by both methods. Four (0.6%) specimens were positive by the NGpapLC assay only. For the cervical and urethral swabs, the NGpapLC provided 100% sensitivity and 100% specificity compared with bacterial culture. Following discrepant analysis, the clinical sensitivity and specificity of the NGpapLC for throat and rectal swabs was also 100%. For the bacterial panel, only N. gonorrhoeae isolates provided positive results. The results show the NGpapLC assay is suitable for use on a range of clinical specimens and could improve detection of pharyngeal N. gonorrhoeae.

Evaluation of conventional and real-time PCR assays using two targets for confirmation of results of the COBAS AMPLICOR Chlamydia trachomatis/Neisseria gonorrhoeae test for detection of Neisseria gonorrhoeae in clinical samples

Two conventional PCR-enzyme immunoassays (PCR-EIAs) and two real-time PCR assays (LightCycler system; Roche Diagnostics) were evaluated as confirmation assays with cppB and 16S rRNA genes as targets. Of 765 male and female genitourinary and nasopharyngeal specimens positive for Neisseria gonorrhoeae in the COBAS AMPLICOR Chlamydia trachomatis/Neisseria gonorrhoeae PCR test (Roche Diagnostics), 229 (30%) were confirmed positive; 13 of these (5.7%) were lacking the cppB gene. Of the 534 samples (70%) that could not be confirmed, 81 (15%) showed a positive crossing point. However, melting curve analysis revealed an aberrant melting temperature in the LightCycler 16S rRNA assay; therefore, these samples were considered non-N. gonorrhoeae Neisseria species. Both of the 16S rRNA assays performed well, with positive predictive values of 99.1% and 100% for the PCR-EIAs and the real-time assays, respectively, and a negative predictive value of 99.8% for both. The cppB assays were compromised by the absence of the cppB gene in 5.7% of the N. gonorrhoeae-positive samples, resulting in negative predictive values of 96.8% and 97.6% for the PCR-EIAs and the real-time assays, respectively. Therefore, the 16S rRNA gene is preferable to the cppB gene as a target for confirmation assays. The melting curve analysis of the real-time assays provides useful additional information.

Comparison of COBAS AMPLICOR Neisseria gonorrhoeae PCR, including confirmation with N. gonorrhoeae-specific 16S rRNA PCR, with traditional culture

A total of 3,023 clinical specimens were tested for Neisseria gonorrhoeae by using COBAS AMPLICOR (CA) PCR and confirmation of positives by N. gonorrhoeae-specific 16S rRNA PCR. The sensitivity of CA plus 16S rRNA PCR was 98.8%, compared to 68.2% for culture. Confirmation of CA positives increased the positive predictive value from 54.8 to 96.6%.

Mycoplasma genitalium: an organism commonly associated with cervicitis among west African sex workers

OBJECTIVES

To identify the contribution of Mycoplasma genitalium to the aetiology of cervicitis in sub-Saharan Africa and its relative importance in the overall burden of sexually transmitted infections among female sex workers (FSW).

METHODS

The study population consisted of FSW recruited in Ghana and Benin during the initial visit of a randomised controlled trial. A questionnaire was administered, a pelvic examination carried out, and cervical samples obtained for detection of M genitalium, Neisseria gonorrhoeae, Chlamydia trachomatis, and Trichomonas vaginalis. Clinical signs potentially indicating cervicitis were cervical discharge, pus on the cervical swab, bleeding after sampling, and inflammatory cervix.

RESULTS

Among 826 FSW, 26.3% were infected with M genitalium. N gonorrhoeae was strongly and independently associated with each of the four signs of cervicitis (adjusted odds ratios (AOR): 4.1 to 6.0). The AOR for C trachomatis were intermediate (1.3-4.1) and the AOR for M genitalium were lower (between 1.6 and 1.8) but statistically significant (p< or =0.05) for each sign.

CONCLUSIONS

M genitalium is weakly associated with signs of cervicitis in west African FSW but is highly prevalent.

Multicenter validation of the cppB gene as a PCR target for detection of Neisseria gonorrhoeae

The cppB gene is often used as a target for detection of Neisseria gonorrhoeae by PCR. Using a coded panel of 500 DNA samples, we determined that the cppB gene is missing in 5.8% of N. gonorrhoeae strains, and therefore we consider the cppB gene to be an unsuitable target.

Positive predictive value of Gen-Probe APTIMA Combo 2 testing for Neisseria gonorrhoeae in a population of women with low prevalence of N. gonorrhoeae infection

We collected specimens from women who tested positive for Neisseria gonorrhoeae using the Gen-Probe APTIMA Combo 2 (AC2), and we performed confirmatory tests using a nucleic acid amplification test (NAAT) that targets alternate gonococcal nucleic acid sequences. Among 59,664 specimens, 280 (0.47%) had positive results using AC2; 265 of these specimens were tested using the confirmatory NAAT, of which 258 yielded positive results (positive predictive value, 97.4%; 95% confidence interval, 95.1%-98.8%). Routine confirmatory testing of specimens with positive AC2 gonorrhea test results is not indicated.