Evaluation of sensitivity of 10 diagnostic assays for Chlamydia trachomatis by use of a simple laboratory procedure

Prevalence of Chlamydia infection among women visiting a gynaecology outpatient department: evaluation of an in-house PCR assay for detection of Chlamydia trachomatis

Background

Screening women for Chlamydia trachomatis infection in developing countries is highly desirable because of asymptomatic infection. The existing diagnostic methods in developing countries are not effective and their sensitivity fall below 45.0% which leads to further spread of infection. There is an urgent need for improved and cost effective diagnostic tests that will reduce the burden of sexually transmitted infections in the developing world.

Methods

Prevalence of C. trachomatis infection among women visiting gynaecology department of Hindu Rao hospital in Delhi, India was determined using Roche Amplicor Multi Well Plate kit (MWP) as well as using in-house PCR assay. We used 593 endocervical swabs for clinical evaluation of the in-house developed assay against Direct Fluorescence Assay (DFA; Group I n = 274) and Roche Amplicor MWP kit (Group II, n = 319 samples) and determined the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) of the in-house developed assay.

Results

We detected 23.0% positive cases and there was a higher representation of women aged 18-33 in this group. An in-house PCR assay was developed and evaluated by targeting unique sequence within the gyrA gene of C. trachomatis. Specificity of the reaction was confirmed by using genomic DNA of human and other STI related microorganisms as template. Assay is highly sensitive and can detect as low as 10 fg of C. trachomatis DNA. The resolved sensitivity of in-house PCR was 94.5% compared with 88.0% of DFA assay. The high specificity (98.4%) and sensitivity (97.1%) of the in-house assay against Roche kit and availability of test results within 3 hours allowed for immediate treatment and reduced the risk of potential onward transmission.

Conclusions

The in-house PCR method is cost effective (~ 20.0% of Roche assay) and hence could be a better alternative for routine diagnosis of genital infection by C. trachomatis to facilitate improved screening and treatment management.

Comparison of an in-house PCR assay, direct fluorescence assay and the Roche AMPLICOR Chlamydia trachomatis kit for detection of C. trachomatis

To improve the control of Chlamydia trachomatis infection in India, a rapid, specific and cost-effective method is much needed. We developed an in-house PCR assay by targeting a unique genomic sequence encoding a protein from the C. trachomatis phospholipase D endonuclease superfamily that produces an amplified fragment of 368 bp. The specificity of the primers was confirmed using genomic DNA from other sexually transmitted disease-causing and related micro-organisms and from humans. The assay was highly sensitive and could detect as low as 10 fg C. trachomatis DNA. Clinical evaluation of the in-house-developed PCR was carried out using 450 endocervical specimens that were divided in two groups. In group I (n=274), in-house PCR was evaluated against the direct fluorescence assay. The resolved sensitivity of the in-house PCR method was 97.22 % compared with 88 % for the direct fluorescent antibody assay. In group II (n=176), the in-house PCR was compared with the commercial Roche AMPLICOR MWP CT detection kit. The resolved sensitivity of the in-house PCR assay reported here was 93.1 % and the specificity was 97.46 %, making it a cost-effective alternative for routine diagnosis of genital infection by C. trachomatis. The method should facilitate early detection leading to better prevention and treatment of genital infection in India.

Production and characterization of monoclonal antibodies to Chlamydia trachomatis

In order to develop an indigenous and reliable immunodiagnostic assay for Chlamydia trachomatis in India, monoclonal antibodies (MAbs) were developed. Serovar D of C. trachomatis (which was previously isolated from the genital tract of infected women) was propagated, purified, and used for production of monoclonal antibody. A total of 12 murine hybrid clones producing immunoglobulin G (IgG) class monoclonal antibodies to C. trachomatis (species-specific, B serogroup-specific, and serovar-specific) were developed. Enzyme-linked immunosorbent assay (ELISA) was used to screen developed murine MAbs with C. trachomatis antigen. Dot-ELISA was used to check the specificity of clones and was used for selecting hybridomas that produced anti-C. trachomatis MAb. There was no cross-reactivity of species-specific, B serogroup-specific, and D serovar-specific anti-major outer membrane protein (MOMP) monoclonal antibodies with other species of Chlamydiae i.e., C. pneumoniae and C. psitacci. Immunoblotting was done for further characterization of six of these clones, i.e., B2.2 and D5.1 (B serogroup-specific), D10.4 and G1.5 (species-specific), and H5.6 and E4.2 (D serovar-specific). Three of these clones D10.4 (species-specific), B2.2 (B serogroup-specific), and H5.6 (D serovar-specific) which reacted with 40 kd MOMP protein in Immunoblotting were used for further screening to detect C. trachomatis in endocervical specimens. The percent positivity with these clones for detection of C. trachomatis antigen by enzyme immunoassay (EIA) was 45% with D10.4, 43% with H5.6, and 35% with B2.2, while 46% of the specimens were found positive by cell culture method. This indicates a high prevalence of C. trachomatis infection in the female genital tract. The sensitivity and specificity of developed anti- MOMP monoclonal antibody in EIA for chlamydial antigen detection was 91.3% and 94.4% for D10.4 clone (species-specific), 91.30% and 98.1% for H5.6 (D serovar-specific) and 75.00% and 99.07% for B2.2 (B serogroup-specific) compared to cell culture method.

Evaluation of near patient testing for Chlamydia trachomatis in a pregnancy termination service

AIM

To identify and evaluate advantages and disadvantages of a near patient test (NPT) for Chlamydia trachomatis, using Clearview Chlamydia MF (Unipath Ltd) in a British Pregnancy Advisory Service (BPAS) clinic.

METHOD

The improved Clearview Chlamydia MF test was used to test endocervical swabs from 400 women attending BPAS clinic for termination of pregnancy. The results were compared with Ligase Chain Reaction (LCR), using Polymerase Chain Reaction (PCR) as the arbiter.

RESULTS

Twenty-seven women tested positive by Clearview Chlamydia MF (24 confirmed by LCR) and 32 by LCR.

COMMENT

NPT has potential advantages in specific situations where a quick result is required for optimal management of those testing positive. However, the current technology available for detection of Chlamydial infection results in time constraints, which limited its benefits in this study, where there was a high throughput of clients. A significant number of cases were missed by Clearview Chlamydia MF, though the sensitivity found is within the ranges reported for various enzyme immunoassays (EIA) - currently the most commonly used testing method. The study confirmed the high positivity in those attending for termination, especially in under 25-year-olds.

Chlamydia trachomatis infection: incidence, health costs and prospects for vaccine development

Chlamydia trachomatis infection is now the most common sexually transmitted disease worldwide. World Health Organisation figures estimated that 89 million new cases of genital Chlamydia infections occurred in 1995, highlighting the worldwide prevalence of infections and the economic burden on healthcare delivery. A number of methods have been developed for detection of chlamydial infection, which vary in sensitivity and specificity. No single method has yet gained general acceptance and in many countries Chlamydia infections are not reported, suggesting that the above figures may be an underestimate of the problem. As yet there is no consensus as to what constitutes a protective immune response against genital Chlamydia infection. Studies in animal models have shown that cell-mediated immunity, both Th1-driven macrophage activation and cytotoxic T cell responses, as well as antibody can mediate protection at different stages of the chlamydial life cycle. A successful vaccine would probably need to elicit both a systemic cell-mediated immune response to limit/resolve established infections and a mucosal IgA response to reduce bacterial shedding and the resulting spread of infection to partners of infected individuals. The immune response to Chlamydia, either through natural infection or following immunisation, also has the potential to enhance inflammation and to act as a driving force for constant mutation in the variable regions of the major outer membrane protein. As a result a constant prevalence of infection is maintained even in an immune population through the emergence of new allelic variants. Immune responses against antigens such as the 60 kDa heat shock protein can exacerbate inflammation through molecular mimicry and must not be elicited as a result of vaccination. Thus there are many challenges for the development of a successful vaccine which must elicit immunity against multiple serovars while at the same time minimising damaging pro-inflammatory immune responses.

Diagnosis of Chlamydia trachomatis and Neisseria gonorrhoeae. Genitourinary infections in males by the Amplicor PCR assay of urine

The Amplicor CT/NG polymerase chain reaction (PCR) test on urine specimens from males was prospectively evaluated against established specimens and laboratory methods for diagnosing Chlamydia trachomatis and Neisseria gonorrhoeae genitourinary infections, in patients from a remote region of Western Australia. Seventy-three males who were tested for both C. trachomatis and N. gonorrhoeae by both conventional methodology and Amplicor PCR on urine were enrolled in the study. Established testing comprised enzyme immunoassay/immunofluorescence antigen testing (EIA/IF) for C. trachomatis and microscopy and/or culture for N. gonorrhoeae on urethral swabs. Positive test results were confirmed using a set of criteria that included supplemental PCR testing and clinical history. Overall, 13.7% of patients were resolved as positive for C. trachomatis and 52.1% as positive for N. gonorrhoeae. The sensitivity and specificity of the Amplicor CT/NG PCR on male urine specimens for C. trachomatis were 80.0% (8/10) and 95.2% (60/63), compared with 60.0% (6/10) and 100.0% (63/63) for EIA/IF on urethral swabs. For N. gonorrhoeae, the sensitivity and specificity of the Amplicor CT/NG PCR on male urine specimens were both 100% (38/38 and 35/35, respectively) compared with 86.8% (33/38) and 100% (35/35) for microscopy and/or culture on urethral swabs. The results of this study indicate that the Amplicor CT/NG multiplex PCR test for C. trachomatis and N. gonorrhoeae performed on urine in males provides a highly sensitive, specific, and robust method for the diagnosis of both C. trachomatis and N. gonorrhoeae, for the early detection of both symptomatic and asymptomatic infected individuals.

Current methods of laboratory diagnosis of Chlamydia trachomatis infections

Infections caused by Chlamydia trachomatis are probably the most common sexually transmitted diseases in the United States. Commonly unrecognized and often inadequately treated, chlamydial infections can ascend the reproductive tract and cause pelvic inflammatory disease, which often results in the devastating consequences of infertility, ectopic pregnancy, or chronic pelvic pain. C. trachomatis infections are also known to increase the risk for human immunodeficiency virus infection. The obligate intracellular life cycle of C. trachomatis has traditionally required laboratory diagnostic tests that are technically demanding, labor-intensive, expensive, and difficult to access. In spite of these historical challenges, however, laboratory diagnosis of C. trachomatis has been a rapidly advancing area in which there is presently a wide array of commercial diagnostic technologies, costs, manufacturers. This review describes and compares the diagnostic methods for C. trachomatis infection that are currently approved for use in the United States, including the newest DNA amplification technologies which are yet to be licensed for commercial use. Issues to consider in selecting a test for purposes of screening versus diagnosis based on prevalence, performance, legal, social, and cost issues are also discussed.

Prevalence and serovar distribution of asymptomatic cervical Chlamydia trachomatis infections as determined by highly sensitive PCR

The prevalence rates and serovar distributions of Chlamydia trachomatis cervical infections were investigated in two different groups of women. Group I consisted of 393 asymptomatic young women (aged 17 to 30 years) who were invited to participate in a C. trachomatis screening program. Group II consisted of 734 randomly selected patients (aged 17 to 68 years) attending an inner-city gynecological outpatient clinic. C. trachomatis was detected in cervical scrapes by PCR specific for endogenous plasmid. These plasmid PCR-positive samples were subsequently subjected to genotyping by C. trachomatis-specific omp1 PCR-based restriction fragment length polymorphism analysis (J. Lan, J. M. M. Walboomers, R. Roosendaal, G. J. van Doornum, D. M. MacLaren, C. J. L. M. Meijer, and A. J. C. van den Brule, J. Clin. Microbiol. 31:1060-1065, 1993). The overall prevalence rates of C. trachomatis found in patients younger than 30 years were 9.2 and 11.8% in groups I and II, respectively. A clear age dependency was seen in group II, with the highest prevalence rate (20%) found in patients younger than 20 years, while the rate declined significantly after 30 years of age (5.9%). In women younger than 30 years, the genotyping results showed that serovars E, I, and D (in decreasing order) were frequent in group I, while serovars F, E, and G (in decreasing order) were predominantly found in group II. The study shows that C. trachomatis infections are highly prevalent in asymptomatic young women. The different serovar distributions found most likely reflect the different compositions of the study groups, but additional analysis of the case histories of individual patients suggests that certain serovars might be associated with symptomatic (i.e., serovar G) or asymptomatic (i.e., serovars D and I) infections.

General practice update: chlamydia infection in women

The prevalence of cervical Chlamydia trachomatis infection in general practice populations ranges between 2% and 12%. Untreated infection can cause pelvic inflammatory disease, tubal infertility and ectopic pregnancy. These risks are increased by cervical invasive procedures, especially termination of pregnancy. However, most women with chlamydia infection have no symptoms. General practitioners and practice nurses carrying out pelvic examinations should have facilities for taking endocervical specimens for chlamydia. Routine chlamydia screening, should be considered if the local prevalence of infection is over 6%. Otherwise chlamydia testing should be offered to women requesting termination of pregnancy and to those who have risk factors: aged less than 25 years, absence of barrier contraception, recent change of sexual partner, vaginal discharge, friable cervix or sterile pyuria. Women found to have chlamydia infection need appropriate antibiotics, advice about contact tracing and referral to a genitourinary medicine clinic. Good communication between general practitioners and genitourinary physicians is essential. Both general practitioners and practice nurses have an important role to play in reducing the prevalence of cervical chlamydia infection and its potentially devastating consequences.