Evaluation of COBAS AMPLICOR (Roche): accuracy in detection of Chlamydia trachomatis and Neisseria gonorrhoeae by coamplification of endocervical specimens

Molecular Approaches to the Diagnosis of Chlamydia

Chlamydia trachomatis is known as the most common bacterial infection agent to pass with sexual transition. This microorganism is an obligatory intracellular parasite. A variety of infections are caused by C. trachomatis, including trachoma, pneumonias in newborns, genital and urinary tract infections, and lymphogranuloma venereum (LGV), which is caused by LGV strains. The diagnosis of Chlamydia trachomatis can be made by cultures and isolations, antigens and antibodies (direct fluorescence, enzyme immunoassays), hybridization, or polymerase chain reaction (PCR). Each year, infection and diagnosis rates increase in the developed world. Since Chlamydia is mostly asymptomatic, screening, and treatment are a key to detecting cases. Polymerase chain reaction (PCR), ligase chain reaction (LCR), and nucleic acid sequence-based amplification (NASBAa) molecular methods can be used for the detection, low concentration, quantification, and identification of organisms. While the traditional PCR method confirms its existence, it can quantify real-time PCR (RT-PCR). This method (RT-PCR) may have low sensitivity among variants of the same species. Also, PCR scans, which receive urine service, offer great advantages. PCR from initial void urine (FVU) samples is highly sensitive in detecting the organism. Urine Chlamydia screenings are more acceptable in large populations and asymptomatic detections.

Diagnosis of Chlamydia trachomatis genital infections in the era of genomic medicine

PURPOSE

Chlamydial genital infections constitute significant sexually transmitted infections worldwide. The often asymptomatic status of C. trachomatis (CT) infections leads to an increased burden on human reproductive health, especially in middle- and low-income settings. Early detection and management of these infections could play a decisive role in controlling this public health burden. The objective of this review is to provide an insight into the evolution of diagnostic methods for CT infections through the development of new molecular technologies, emphasizing on -omics' technologies and their significance as diagnostic tools both for effective patient management and control of disease transmission.

METHODS

Narrative review of the diagnostic methodologies of CT infections and the impact of the introduction of -omics' technologies on their diagnosis by review of the literature.

RESULTS

Various methodologies are discussed with respect to working principles, required specifications, advantages, and disadvantages. Implementing the most accurate methods in diagnosis is highlighted as the cornerstone in managing CT infections.

CONCLUSION

Diagnostics based on -omics' technologies are considered to be the most pertinent modalities in CT testing when compared to other available methods. There is a need to modify these effective and accurate diagnostic tools in order to render them more available and feasible in all settings, especially aiming on turning them to rapid point-of-care tests for effective patient management and disease control.

A systematic review and meta-analysis of different diagnostic procedures to detect gonococcus infection in resource-limited scenario

Context

Neisseria gonorrhoeae is a Gram-negative diplococcus, an obligate human pathogen, and the etiologic agent of the sexually transmitted infection (STI), gonorrhoea. culture is the standard procedure for diagnosis, which may be supported by nucleic acid tests and microscopy.

Aims

To determine the best possible method of diagnosis for Gonococcus infection in resource-limited settings.

Settings and Design

The meta-analyses were designed to determine the difference in diagnosis between Culture and nucleic acid amplification tests (NAATs) and also between the different Amplification Tests and widely available Roche COBAS AMPLICOR test.

Subjects and Methods

Databases searched were Pubmed, Medline, Google Scholar and Cochrane reviews. Risk ratio (RR) with 95% confidence intervals was estimated for the dichotomous outcomes. The random-effect model was applied for all the studies in the analysis.

Statistical Analysis Used

The meta-analysis was computed in RevMan Version 5.3, Copenhagen, Denmark.

Results

In the first analysis, NAATs significantly improved the chances of detection in comparison to the standard culture and final RR was 1.24 (1.05-2.51), which put the diamond on the right of no-effect axis, indicating more positives by NAATs. In the second analysis, AMPLICOR had the more positive results, which may have indicated better detection rate, as well as less specificity and final RR was 0.809 (0.737-0.888), which put the diamond on the left of the non-effect axis, indicating more positives by AMPLICOR.

Conclusions

In a resource-limited scenario like India, the syndromic management of STIs are considered to be the norm. A positive diagnosis is only given if the tests are confirmed by Culture, as it is still considered to be the gold standard of diagnosis. However, in many cases, due to suboptimal transportation and lack of proper handling, culture in unable to grow even if the patient is infected. In such cases, Nucleic Acid Tests should be able to detect an infection.

Ureaplasma urealyticum and U. parvum in sexually active women attending public health clinics in Brazil

Ureaplasma urealyticum and U. parvum have been associated with genital infections. The purpose of this study was to detect the presence of ureaplasmas and other sexually transmitted infections in sexually active women from Brazil and relate these data to demographic and sexual health, and cytokines IL-6 and IL-1β. Samples of cervical swab of 302 women were examined at the Family Health Units in Vitória da Conquista. The frequency of detection by conventional PCR was 76·2% for Mollicutes. In qPCR, the frequency found was 16·6% for U. urealyticum and 60·6% U. parvum and the bacterial load of these microorganisms was not significantly associated with signs and symptoms of genital infection. The frequency found for Trichomonas vaginalis, Neisseria gonorrhoeae, Gardnerella vaginalis and Chlamydia trachomatis was 3·0%, 21·5%, 42·4% and 1·7%, respectively. Higher levels of IL-1β were associated with control women colonized by U. urealyticum and U. parvum. Increased levels of IL-6 were associated with women who exhibited U. parvum. Sexually active women, with more than one sexual partner in the last 3 months, living in a rural area were associated with increased odds of certain U. parvum serovar infection.

Gonorrhoea diagnostics: An update

Diagnosis of gonorrhoea is an ongoing challenge. The organism is fastidious requiring meticulous collection and transport for successful cultivation. Asymptomatic infections are common which go undetected by conventional methods thereby leading to continued transmission and the risk of complications. The nucleic acid amplification tests, now increasingly used in developed countries, offer improved sensitivity compared to bacterial culture. However, these continue to suffer sequence related problems leading to false positive and false negative results. Further, these cannot be used for generation of data on antibiotic susceptibility because genetic markers of antibiotic resistance to recommended therapies have not been fully characterised. They are unaffordable in a setting like ours where reliance is placed on syndromic approach for sexually transmitted infection (STI) management. The use of syndromic approach has resulted in a considerable decline in the number of Neisseria gonorrhoeae isolates that have been cultured for diagnostic purposes. Many laboratories formerly doing so are no longer performing culture for gonococci, and the basic skills have been lost. There is a need to not only revive this skill but also adopt newer technologies that can aid in accurate diagnosis in a cost-effective manner. There is room for innovation that can facilitate the development of a point-of-care test for this bacterial STI.

Tracking false-negative results in molecular diagnosis: proposal of a triplex-PCR based method for leishmaniasis diagnosis

Background

Molecular biological methods have become increasingly relevant to the diagnosis and control of infectious diseases, such as leishmaniasis. Since various factors may affect the sensitivity of PCR assays, including DNA yield and purity, an optimal extraction method is pivotal. Losses of a parasite’s DNA during extraction may significantly impair its detection by PCR and lead to false-negative results. This study proposes a triplex PCR assay targeting the parasite’s DNA, an external control (pUC18) and an internal control (G3PD) for accurate diagnosis of leishmaniasis.

Results

Two primer pairs were designed to detect the plasmid pUC18 and a triplex PCR assay targeting the Leishmania braziliensis kinetoplast DNA, the external control and the internal control was standardized. The triplex PCR assay was assessed for its ability to detect the three target DNA fragments simultaneously.

PCR products from pUC18 DNA resulted in bands of 368 (P1) and 316 (P2) base pairs (bp). The triplex PCR optimized with the chosen external control system (P1) allowed the simultaneous detection of the internal control (G3PD – 567 bp) as well as of small quantities (10 pg) of the target parasite’s DNA, detected by amplification of a 138 bp product.

Conclusions

The new tool standardized herein enables a more reliable interpretation of PCR results, mainly by contributing to quality assurance of leishmaniasis diagnosis. Furthermore, after simple standardization steps, this protocol could be applied to the diagnosis of other infectious diseases in reference laboratories. This triplex PCR enables the assessment of small losses during the DNA extraction process, problems concerning DNA degradation (sample quality) and the detection of L. braziliensis kDNA.

Low prevalence of Chlamydia trachomatis infection in non-urban pregnant women in Vellore, S. India

Objective

To determine the prevalence and risk factors for Chlamydia trachomatis (CT) infection in pregnant women and the rate of transmission of CT to infants.

Methods

Pregnant women (≥28 weeks gestation) in Vellore, South India were approached for enrollment from April 2009 to January 2010. After informed consent was obtained, women completed a socio-demographic, prenatal, and sexual history questionnaire. Endocervical samples collected at delivery were examined for CT by a rapid enzyme test and nucleic acid amplification test (NAAT). Neonatal nasopharyngeal and conjunctival swabs were collected for NAAT testing.

Results

Overall, 1198 women were enrolled and 799 (67%) endocervical samples were collected at birth. Analyses were completed on 784 participants with available rapid and NAAT results. The mean age of women was 25.8 years (range 18–39 yrs) and 22% (95% CI: 19.7–24.4%) were primigravida. All women enrolled were married; one reported >one sexual partner; and six reported prior STI. We found 71 positive rapid CT tests and 1/784 (0.1%; 95% CI: 0–0.38%) true positive CT infection using NAAT.

Conclusions

To our knowledge, this is the largest study on CT prevalence amongst healthy pregnant mothers in southern India, and it documents a very low prevalence with NAAT. Many false positive results were noted using the rapid test. These data suggest that universal CT screening is not indicated in this population.

The laboratory diagnosis of Neisseria gonorrhoeae

The present article describes the laboratory diagnosis of Neisseria gonorrhoeae by culturing of the organism from different types of clinical specimens followed by confirmatory tests. The success of culture methods requires good quality collection and transport of clinical specimens. The present guide describes the media requirements and cultural conditions for N gonorrhoeae growth and the characteristics for a presumptive identification of N gonorrhoeae. Confirmatory tests include biochemical tests, chromogenic enzyme substrate tests, immunoassays and nucleic acid methods. Nucleic acid detection methods include either amplification-based methods or nonamplification tests, and are increasingly used in clinical laboratories where a viable culture is not possible to obtain. Nucleic acid methods can also be used to detect the presence of low numbers in a specimen. Nucleic acid detection methods need confirmation with another amplification method or gene target. Controls must be included to ensure true positive and negative results, and to rule out nucleic acid contamination. Monitoring of antimicrobial susceptibilities of N gonorrhoeae is important to investigate treatment failure and to evaluate the efficacy of currently recommended therapies. Many methods for the characterization of N gonorrhoeae require cultures. The useful typing methods for determining strain relatedness include auxotyping, serotyping, plasmid profile analysis, DNA sequencing of the porB gene and pulsed-field gel electrophoresis. Quality assurance programs for diagnostic testing and antimicrobial susceptibility testing is reviewed.

Molecular Diagnosis of Sexually Transmitted Chlamydia trachomatis in the United States

Chlamydia, with its Chlamydia trachomatis etiology, is the most common bacterial sexually transmitted infection in the United States and is often transmitted via asymptomatic individuals. This review summarizes traditional and molecular-based diagnostic modalities specific to C. trachomatis. Several commercially available, FDA-approved molecular methods to diagnose urogenital C. trachomatis infection include nucleic acid hybridization, signal amplification, polymerase chain reaction, strand displacement amplification, and transcription-mediated amplification. Molecular-based methods are rapid and reliable genital specimen screening measures, especially when applied to areas of high disease prevalence. However, clinical and analytical sensitivity for some commercial systems decreases dramatically when testing urine samples. In vitro experiments and clinical data suggest that transcription-mediated amplification has greater analytical sensitivity than the other molecular-based methods currently available. This difference may be further exhibited in testing of extragenital specimens from at-risk patient demographics. The development of future molecular testing could address conundrums associated with confirmatory testing, medicolegal testing, and test of cure.

A German Chlamydia trachomatis screening program employing semi-automated real-time PCR: results and perspectives

BACKGROUND

Genital Chlamydia trachomatis infection is a worldwide public health burden. A screening program for C. trachomatis was therefore initiated by the public health insurers in Germany ("Gemeinsamer Bundesausschuss", GBA) in April 2008.

OBJECTIVES

To estimate C. trachomatis prevalence from screening 115,766 asymptomatic females and 20,033 female patients with unspecific abdominal pain.

STUDY DESIGN

Urine samples (pooled by five for the asymptomatic screening subjects) and cervical swabs were analyzed using semi-automated real-time PCR. Infection prevalence was determined separately in four categories of women, defined by health status (asymptomatic screening vs. non-screening with unspecified symptoms) and test material used. Comparative analyses were stratified by age and pregnancy status.

RESULTS

Experimental evaluation of the assay used revealed a detection limit of 379 genome copies/ml urine. For pooled urine samples, the positive predictive value was 100% whereas the negative predictive value equaled 98.1%. The observed infection prevalence was higher for cervical swabs than for urine samples. Prevalence estimates also differed significantly between pregnant and non-pregnant adolescents (< or = 20 years), irrespective of the test material used (10.2% vs. 7.3% for cervical swabs, 10.9% vs. 6.1% for pooled urine samples).

CONCLUSIONS

Our retrospective study, based upon a very large number of females from all parts of Germany, revealed a high infection prevalence in adolescents, particularly in pregnant adolescents, thereby justifying the screening directive of the German GBA.

Evaluation of an automated extraction method for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae by Cobas Amplicor PCR from different sample materials

A commercially available automated device (MagNA Pure LC) was adapted for nucleic acid extraction of urogenital specimen for subsequent PCR detection of Chlamydia trachomatis and Neisseria gonorrhoeae in a clinical laboratory. Results were compared to the standard manual extraction procedure and showed excellent correlation, with even slightly increased sensitivity.

Primary health care providers surveyed commonly misinterpret 'first void urine' for chlamydia screening

An open question survey of general practitioners (GP) and hospital emergency department (ED) doctors revealed that the term ‘FVU’ (first void urine) used for urine chlamydia testing, is ambiguous, potentially leading to incorrect urine sample collection and barriers to effective screening. The results of this survey indicate that only 4.3% (95% confidence interval [CI] 0.5–14.5%) of GP and 6.9% (95% CI 0.9–22.8%) of ED doctors respectively, correctly interpreted the meaning of FVU. The majority of clinicians surveyed misunderstood ‘FVU’ to require the first urine void of the day, accounting for 68.1% (95% CI 52.9–80.9%) of GP responses and 37.9% (95% CI 20.7–57.7%) of ED doctors responses. This highlights the need for clarification and standardisation of terminology used in urine chlamydia screening for health care providers, in order to optimise strategies for diagnosis and control of the ongoing chlamydia epidemic.

Male circumcision and women's risk of incident chlamydial, gonococcal, and trichomonal infections

BACKGROUND

Male circumcision (MC) decreases the risk of human immunodeficiency virus (HIV) acquisition in men. We explored associations between MC of the primary sex partner and women's risk of acquisition of chlamydial (Ct), gonococcal (GC), or trichomonal (Tv) infections.

METHODS

We analyzed data from a prospective study on hormonal contraception and incident human immunodeficiency virus/sexually transmitted infection (STI) among women from Uganda, Zimbabwe, and Thailand. At enrollment and each follow-up visit, we collected endocervical swabs for polymerase chain reaction identification of Ct and GC; Tv was diagnosed by wet mount. Using Cox proportional hazards models, we compared time to STI acquisition for women according to their partner's MC status.

RESULTS

Among 5925 women (2180 from Uganda, 2228 from Zimbabwe, and 1517 from Thailand), 18.6% reported a circumcised primary partner at baseline, 70.8% reported an uncircumcised partner, and 9.7% did not know their partner's circumcision status. During follow-up, 408, 305, and 362 participants had a first incident Ct, GC, or Tv infection, respectively. In multivariate analysis, after controlling for contraceptive method, age, age at coital debut, and country, the adjusted hazard ratio (HR) comparing women with circumcised partners with those with uncircumcised partners for Ct was 1.25 [95% confidence interval (CI) 0.96-1.63]; for GC, adjusted HR 0.99 (95% CI 0.74-1.31); for Tv, adjusted HR 1.05 (95% CI 0.80-1.36), and for the 3 STIs combined, adjusted HR 1.02 (95% CI 0.85-1.21).

CONCLUSIONS

MC was not associated with women's risk of acquisition of Ct, GC, or Tv infection in this cohort.

Antenatal lower genital tract infection screening and treatment programs for preventing preterm delivery

BACKGROUND

Preterm birth is birth before 37 weeks' gestation. Genital tract infection is one of the causes of preterm birth. Infection screening during pregnancy has been used to reduce preterm birth. However, infection screening may have some adverse effects, e.g. increased antibiotic drug resistance, increased costs of treatment.

OBJECTIVES

To assess the effectiveness and complications of antenatal lower genital tract infection screening and treatment programs in reducing preterm birth and subsequent morbidity.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (January 2008) and the Cochrane Central Register of Controlled Trials (The Cochrane Library 2007, Issue 2).

SELECTION CRITERIA

We included all published and unpublished randomised controlled trials in any language that evaluated any described methods of antenatal lower genital tract infection screening compared with no screening. Preterm births have been reported as an outcome.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligibility, trial quality and extracted data.

MAIN RESULTS

One study (4155 women) met the inclusion criteria. This trial is of high methodological quality. In the intervention group (2058 women), the results of infection screening and treatment for bacterial vaginosis, trichomonas vaginalis and candidiasis were reported; in the control group (2097 women), the results of the screening program for the women allocated to receive routine antenatal care were not reported. Preterm birth before 37 weeks was significantly lower in the intervention group (3% versus 5% in the control group) with a relative risk (RR) of 0.55 (95% confidence interval (CI) 0.41 to 0.75). The incidence of preterm birth for low birthweight preterm infants with a weight equal to or below 2500 g and very low birthweight infants with a weight equal to or below 1500 g were significantly lower in the intervention group than in the control group (RR 0.48, 95% CI 0.34 to 0.66 and RR 0.34; 95% CI 0.15 to 0.75, respectively).

AUTHORS' CONCLUSIONS

There is evidence that infection screening and treatment programs in pregnant women may reduce preterm birth and preterm low birthweights. Future trials should evaluate the effects of types of infection screening program, gestational ages at screening test and the costs of introducing an infection screening program.

Chronic endometritis in DMPA users and Chlamydia trachomatis endometritis

OBJECTIVE

This study was conducted to determine the prevalence of Chlamydia trachomatis (CT) in the endometrium of depot medroxyprogesterone acetate (DMPA) users with and without breakthrough bleeding (BTB) (unscheduled bleeding) and/or chronic endometritis (CE).

METHODS

Cross-sectional study. Endometrial biopsies were performed on 20 DMPA users who were having BTB and 20 DMPA users who were amenorrheic. The paraffin-embedded tissue sections were washed with xylene and ethanol to remove the paraffin. CT was identified in the endometrial samples using the COBAS AMPLICOR (Roche Diagnostics, Branchburg, NJ, USA) polymerase chain reaction (PCR) identification system.

RESULTS

Chronic endometritis was the most common histologic finding (10/40, 25%) and occurred more often in women experiencing BTB (35% vs. 15%) (RR 1.62, CI 0.91-2.87). No patient with CE had CT infection of the endometrium or cervix.

CONCLUSIONS

CT was not a cause of CE in this population of at-risk patients using DMPA. It is possible that CE in DMPA users reflects an inflammatory state, a function of an atrophic endometrium. This points to the possibility of nonsteroidal anti-inflammatory drugs as therapy for CE in this population rather than antimicrobials or hormonal medication.

Evaluation of Gen-Probe APTIMA-based Neisseria gonorrhoeae and Chlamydia trachomatis confirmatory testing in a metropolitan setting of high disease prevalence

Prompted by reports challenging the validity of the low-positive Neisseria gonorrhoeae and Chlamydia trachomatis results generated by the APTIMA Combo 2 assay (Gen-Probe, Incorporated) and by a Centers for Disease Control and Prevention recommendation to confirm N. gonorrhoeae- or C. trachomatis-positive screens by using an alternative amplification target, we report on a comparison of this means of confirmation with an in-house algorithm of repeat testing. Primary clinical specimens yielding N. gonorrhoeae- or C. trachomatis-specific luminescent values between 100,000 and 1,000,000 were repeat tested in duplicate. A subset of specimens was forwarded for confirmatory assays (Gen-Probe) individualized for alternative N. gonorrhoeae or C. trachomatis targets. An 18-month audit revealed that 230 of 29,977 C. trachomatis screens (0.8%) and 41 of 29,064 N. gonorrhoeae assays (0.1%) yielded low-positive data. When a subset of 40 low-positive N. gonorrhoeae screens was repeat tested, 20 (50.0%) remained positive; 22 (55.0%) of the screens remained positive following performance of the confirmatory assay. In contrast, repeat testing of 153 low-positive C. trachomatis screens yielded a positive result for fewer specimens (n = 97; 63.4%) than when commercial confirmatory testing was used (n = 124; 81.0%). However, confirmation of the results for additional C. trachomatis screens by use of an alternative target did not translate into significant differences in the calculated overall C. trachomatis-positive screen rates (7.39% by repeat testing versus 7.52% by the confirmatory assay; P = 0.53). Furthermore, use of the confirmatory assay raised the positive predictive value only 1.8% over that of repeat testing. Molecular confirmatory testing did not significantly enhance the reliability of C. trachomatis- or N. gonorrhoeae-specific nucleic acid amplification testing in this metropolitan setting compared to the reliability of repeat testing.

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.

Urine gonococcal/Chlamydia testing in adolescents

PURPOSE OF REVIEW

This review will highlight the recent literature findings regarding urine-based Chlamydia and gonorrhea testing in adolescents.

RECENT FINDINGS

Rates of Chlamydia trachomatis are increasing, likely due to increased detection efficiency, but have not yet begun to decrease. Neisseria gonorrhoeae is at an all-time low. Urine-based testing for sexually transmitted infections is readily available and convenient but underutilized. Interesting approaches to a more universal screening program, including self-collected, mail-in urine samples, have been shown to be effective.

SUMMARY

In spite of recommendations urging universal screening for C. trachomatis and N. gonorrhoeae and the availability of highly accurate and convenient tests, screening rates for adolescents and young adults remain below the universal recommendations. Strategies to improve screening rates should take advantage of urine-based screening methodologies for sexually transmitted infections because of their cost-effectiveness as well as the convenience for patient and provider.

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.

PCR-based diagnostics for infectious diseases: uses, limitations, and future applications in acute-care settings

Molecular diagnostics are revolutionising the clinical practice of infectious disease. Their effects will be significant in acute-care settings where timely and accurate diagnostic tools are critical for patient treatment decisions and outcomes. PCR is the most well-developed molecular technique up to now, and has a wide range of already fulfilled, and potential, clinical applications, including specific or broad-spectrum pathogen detection, evaluation of emerging novel infections, surveillance, early detection of biothreat agents, and antimicrobial resistance profiling. PCR-based methods may also be cost effective relative to traditional testing procedures. Further advancement of technology is needed to improve automation, optimise detection sensitivity and specificity, and expand the capacity to detect multiple targets simultaneously (multiplexing). This review provides an up-to-date look at the general principles, diagnostic value, and limitations of the most current PCR-based platforms as they evolve from bench to bedside.

Is the prevention of genital chlamydial infections by community involvement possible?

This chapter presents different means by which community initiatives have been undertaken to reduce the prevalence and incidence of genital and allied infections caused by Chlamydia trachomatis. As most of these infections in the majority of infected individuals do not produce symptoms that are likely to urge them to attend any health care unit, screening programmes are mandatory to be able to influence the epidemic of infections with this agent. In many societies there has been a skewed gender distribution in the number of chlamydia-positive persons; this probably indicates that diagnostic service activities have been directed more against one gender than the other. The important role of partner notification, as in the case of other sexually transmitted infections, has been documented. Different means of community initiative have included counselling of school children and groups of persons more likely to be infected. Counselling by the pharmacy has an important role in many societies. Selected cohorts have been offered - via the mass media, Internet, radio and television programmes - sampling kits which can be mailed to a laboratory for testing. The establishment of youth clinics has been found effective for detecting teenagers harbouring C. trachomatis, similarly to screening at antenatal clinics. The offer of free consultations, aetiological tests and therapy has been a part of community initiatives, mimicking the services offered for some of the classic sexually transmitted infections. This chapter considers the usefulness of different test methods and stresses the need to retest those found to be positive. Barriers to the successful introduction of screening activities and diagnostic services are also considered.

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

The COBAS AMPLICOR CT/NG test is widely used for the diagnosis of Neisseria gonorrhoeae infection using genital swabs or urine samples. Although highly specific, cross-reactivity occurs with some nonpathogenic strains of Neisseria and Lactobacillus species. In low-prevalence populations, even highly specific assays may require confirmatory testing of positive results. We assessed the positive predictive value (PPV) of this test in a low-prevalence (0.5%) setting. Genital and urine specimens testing positive using the COBAS AMPLICOR NG test were retested using an investigational 16S rRNA PCR assay. Additionally, 737 specimens were tested in parallel by both culture and the above PCR protocol. Of 9,772 specimens tested in-house, 168 were positive by the AMPLICOR test; in addition, 62 AMPLICOR-positive specimens were referred to our laboratory for confirmatory testing, yielding 230 positive specimens. Of these, 72 were confirmed positive by 16S rRNA PCR, yielding a specificity of 98.7% and a PPV of 31.3%. Specificity was similar for all specimen types, whereas PPV varied with prevalence: specimens from males, females, urine specimens, and genital swabs had PPVs of 70.8, 13.3, 51.9, and 20.1%, respectively. The PPV was higher when the initial AMPLICOR optical density (OD) was > or =3.5 versus initial and repeat OD readings in an equivocal zone of > or =0.2 to <3.5 (65.1 versus 10.1%; P < 0.001). On repeat testing of specimens with ODs in the equivocal zone, 54 gave ODs of > or =0.2 and <2.0, 35 gave ODs of > or =2.0 and <3.5, and 12 gave ODs of > or =3.5, with 3.7, 20, and 33.3% confirmed positive, respectively (P = 0.004). Comparing PCR to culture as the "gold standard," specificity increased from 96.8 to 99.9% when 16S rRNA PCR was performed on specimens positive by the COBAS AMPLICOR NG test. Confirmatory testing with a more specific method such as 16S rRNA PCR should be considered in low-prevalence populations, especially for specimens with an OD in the equivocal zone.

Evaluation of the Digene Hybrid Capture II Assay with the Rapid Capture System for detection of Chlamydia trachomatis and Neisseria gonorrhoeae

Screening for chlamydial and gonococcal infection has been strongly recommended for all sexually active women under the age of 26. Advances in the ability to detect infection by nucleic acid detection techniques have improved access to screening methods in routine clinical practices. To meet the increasing demand for testing, a high-throughput system is desirable. We evaluated the performance of the Hybrid Capture 2 CT/GC (HC2) assay with the Digene Rapid Capture System (HC2-RCS). The results of HC2-RCS for endocervical samples from 330 women were compared to those of culture and the COBAS Amplicor PCR. For detection of chlamydial infection, HC2-RCS had a sensitivity and a specificity similar to those of PCR (P > 0.5) and an improved sensitivity compared to that of culture (P = 0.007). For identification of gonococcal infections, all assays performed similarly (P > 0.5). The performance of HC2-RCS was also compared to that of the manual HC2 format (HC2-M) with these samples and with 911 endocervical samples collected previously. The performance of HC2-RCS was equivalent to that of HC2-M; the overall concordance rates for the detection of chlamydia and gonorrhea were 99.7% (kappa = 0.97) and 99.8% (kappa = 0.97), respectively. When the HC2 assay was performed with a semiautomated system application designed for high throughput, it demonstrated high sensitivity and a high specificity for detection of both Chlamydia trachomatis and Neisseria gonorrhoeae.