Diagnosis of urogenital Chlamydia trachomatis infection by use of DNA amplification

Chlamydiaceae in cattle: commensals, trigger organisms, or pathogens?

Epidemiological data indicate that infection of cattle with chlamydiae such as Chlamydophila (C.) pecorum, C. abortus, C. psittaci and Chlamydia suis, is ubiquitous with mixed infections occurring frequently. The apparent lack of association between infection and clinical disease has resulted in debate as to the pathogenic significance of these organisms, and their tendency to sub-clinical and/or persistent infection presents a challenge to the study of their potential effects. However, recent evidence indicates that chlamydial infections have a substantial and quantifiable impact on livestock productivity with chronic, recurrent infections associated with pulmonary disease in calves and with infertility and sub-clinical mastitis in dairy cows. Data also suggest these infections manifest clinically when they coincide with a number of epidemiological risk factors. Future research should: (1) use relevant animal models to clarify the pathogenesis of bovine chlamydioses; (2) quantify the impact of chlamydial infection at a herd level and identify strategies for its control, including sub-unit vaccine development; and (3) evaluate the zoonotic risk of bovine chlamydial infections which will require the development of species-specific serodiagnostics.

Comparative performance of the Roche COBAS Amplicor assay and an in-house real-time PCR assay for diagnosis of Chlamydia trachomatis infection

This study investigated the comparative performance of the Amplicor assay and an in-house semi-automated, multiplex real-time PCR for the diagnosis of genital chlamydial infection. Four different assays, the COBAS Amplicor CT test (Amplicor PCR), in-house real-time PCR (IHRT-PCR), in-house nested cryptic plasmid PCR and in-house nested major outer membrane protein PCR, were performed on genital swabs from 1000 consecutive patients attending a genitourinary medicine clinic. The samples were designated true positive if Chlamydia trachomatis DNA was detected by at least two of the four above-mentioned assays while a sample was defined as true negative if C. trachomatis DNA was detected in only one or none of the assays. By this criterion, there were 129 true positive and 871 true negative samples for C. trachomatis DNA in this cohort. Amplicor PCR designated 144 samples positive: 128 (89%) of 144 samples were true positive and 16 (11%) were false positive. IHRT-PCR detected 126 of 129 true positive samples and did not generate any false positive results. The sensitivity of IHRT-PCR was comparable with, and specificity was higher than, Amplicor PCR for the diagnosis of genital chlamydial infection.

A novel real-time PCR to detect Chlamydia trachomatis in first-void urine or genital swabs

Screening for Chlamydia trachomatis infections can be performed on urine samples and genital swabs using molecular techniques. A novel approach was developed that combined an automated extraction procedure, an automated liquid-handling system and real-time PCR to detect C. trachomatis from urine or swabs. This novel real-time PCR approach was compared to the commercial Cobas Amplicor system on 628 specimens. In a retrospective analysis, 51 samples that tested positive using the Cobas assay were also positive with the real-time PCR, whereas the 49 samples negative with Cobas were also negative with the real-time PCR, for an overall agreement of 100 %. Among 528 prospective samples consecutively received at the authors' laboratory with a request for C. trachomatis PCR, five PCR reactions were inhibited when tested with Cobas. These five inhibited samples were found negative with the real-time PCR. Among the remaining 523 samples, 45 (8.6 %) were positive with both methods, 476 (91 %) were negative with both methods, and 2 (0.4 %) were positive with Cobas but negative with the real-time PCR. Thus, when considering Cobas as the gold standard, the overall agreement was 99.6 %, the sensitivity of the real-time PCR was 95.7 % and the specificity was 100 %. The two discrepant samples were retested in parallel and were found negative with both methods. When testing a batch of 25 samples, both reagent costs and laboratory technician time were reduced with the new technique (7.30 euros per sample and 134 min) compared to Cobas (11.20 euros per sample and 232 min). Moreover, due to reduced organizational constraints, the median time from sample reception to result was only 24 h using the automated platform. Overall, this novel real-time PCR approach exhibited an excellent specificity and a sensitivity similar to that of Cobas Amplicor PCR for the detection of C. trachomatis. Given its high throughput potential and low costs/laboratory technician time requirement, it may be useful for future use in large C. trachomatis screening programs.

Ectopic Pregnancies and Reproductive Capacity After Chlamydia trachomatis Positive and Negative Test Results: A Historical Follow-Up Study

BACKGROUND

Recent studies have shown that women with Chlamydia trachomatis-positive test results worry about their future fertility.

GOAL

The goal of this study was to give women infected with C. trachomatis a fertility prognosis by analyzing ectopic pregnancies and birth rates

STUDY DESIGN

An historical follow-up study in a cohort of 22,264 women tested for the infection was conducted.

RESULTS

Cox regression analysis with time-dependent covariates showed that women with at least 1 C. trachomatis-positive test result had a lower incidence rate of ectopic pregnancy than women with negative test results only (adjusted hazard ratio, 0.55; 95% confidence interval [CI], 0.31-0.96). We found comparable birth rates in the 2 groups (adjusted hazard ratio, 0.92; 95% CI, 0.84-1.00).

CONCLUSIONS

Counseling of women with a C. trachomatis-positive test result should emphasize the benefit of detection and treatment of the infection in terms of future morbidity.

Molecular genetic methods for diagnosis and characterisation of Chlamydia trachomatis and Neisseria gonorrhoeae: impact on epidemiological surveillance and interventions

One of the mainstays in the prevention of Chlamydia trachomatis and Neisseria gonorrhoeae infections is the availability of laboratory diagnostics with high sensitivity and specificity. Assays for diagnosis of C. trachomatis include cell culture and nucleic acid amplification tests (NAATs). The major target sequences for C. trachomatis diagnosis by NAATs are located at the cryptic plasmid and the major target used for characterisation is the omp1 gene. The gold standard for diagnosis of N. gonorrhoeae is culture. However, numerous NAATs for identification of N. gonorrhoeae and a number of molecular genetic methods for characterisation of N. gonorrhoeae have been developed. Probably no routine laboratory can attain as high sensitivity by culturing C. trachomatis or N. gonorrhoeae as by using NAATs. For that reason NAATs can be recommended for diagnosing C. trachomatis, but not as the only diagnostic assay for N. gonorrhoeae, due to lack of antibiotic susceptibility testing and specificity problems, most pronounced for pharyngeal and rectal samples. Genotyping of C. trachomatis or N. gonorrhoeae provides additional information for contact tracing. It is recommended for N. gonorrhoeae, at least in low prevalence geographic areas, but cannot today be recommended for C. trachomatis. This is due to the low genetic variability and hence the limited benefits for partner notification. However, genotyping of C. trachomatis may play an important role under special circumstances.

Reasons for Chlamydia trachomatis testing and the associated age-specific prevalences

OBJECTIVE

to assess the age- and sex-specific prevalence of Chlamydia trachomatis infection according to the indications for testing. This was done as part of a health technology assessment to identify the populations that would benefit most from universal screening, and to identify ongoing potential superfluous testing that could liberate resources to be used for targeted screening programs.

METHODS

In Aarhus County, Denmark, population of 630,000, data were collected on 11,423 persons who were being tested for C. trachomatis (10,351 females and 1072 males). Indicated on the request slip were: the sex, the age and the reasons for testing (infected partner; planned transcervical procedure; symptoms consistent with C. trachomatis infection; or routine testing). All samples were analyzed by the Ligase Chain Reaction.

RESULTS

More than 90% of all the tests were conducted in women. The majority of tests were performed in the 21-25 years age group but the prevalence was highest in the 16-20 years age group (7.2%; 95% CI: 5.4%-9.3%). A total of 25% of all tests were carried out in asymptomatic women above the age of 30 in whom the prevalence was only 1.3% (95% CI: 0.8%-1.9%). More than three times as many women (5.8%) than men (1.7%) were tested as sexual partners to C. trachomatis-infected index patients but the risk of infection was highest among men. In women who were tested prior to a transcervical procedure, the prevalence was highest (5.5%; 95% CI: 1.8%-12.4%) in the 16-20 years age group, whereas most samples were obtained in women aged 31-35 years in whom the prevalence was only 0.8% (0.2%-2.3%).

CONCLUSIONS

The prevalence of C. trachomatis infection justifies the screening of asymptomatic individuals below 30 years of age. At present, however, 25% of all tests are requested in asymptomatic women above the age of 30. It might be advisable to use the resources for systematic universal screening of younger individuals rather than to continue the current opportunistic screening of older women.

Genotyping of Chlamydia trachomatis would improve contact tracing

BACKGROUND

The reported number of Chlamydia trachomatis genital infections has increased 15% annually since 1997 in Sweden. Inaccurate partner notification might be one reason.

GOAL

The goals were to determine if genotyping of C trachomatis would improve partner notification and to study the duration of infection.

STUDY DESIGN

Sexual networks were constructed. C trachomatis isolates from 231 individuals attending the Orebro STD clinic during 1 year were typed by sequencing of the omp1 gene.

RESULTS

All individuals were traced and diagnoses were established in 30 of 161 networks. More than one genotype was seen in seven networks. The mean duration of C trachomatis infection in each network was calculated to be 23 weeks.

CONCLUSION

Genotyping could be a useful tool in partner notification when there are discrepant or uncommon genotypes. Limited clinic catchment areas create information difficulties that obstruct accurate contact tracing.

Microbiological aspects of the diagnosis of Chlamydia trachomatis

The available diagnostic methods for Chlamydia trachomatis infection comprise serology (indirect detection) and culture, antigen detection and nucleic acid amplification (direct detection). The rationale, applications, advantages and disadvantages of the methods and diagnostic targets are discussed. Compared to conventional methods, nucleic acid amplification tests have increased sensitivity. This allows samples to be taken at home by the patient herself and mailed directly to the laboratory. Public health strategies implying home sampling for asymptomatic men and women result in a lower prevalence and a lower risk of short-term complications in terms of pelvic inflammatory disease (PID). The importance of predictive values and the association with prevalence are highlighted.

Characterization of Chlamydia trachomatis omp1 genotypes among sexually transmitted disease patients in Sweden

A method for detection and genotyping of genital Chlamydia trachomatis infections based on omp1 gene amplification and sequencing was developed. DNA was extracted from urogenital or urine samples using a Chelex-based method, and an approximately 1,100-bp-long fragment from the omp1 gene was directly amplified and sequenced. Genotyping was performed by BLAST similarity search, and phylogenetic tree analysis was used to illustrate the evolutionary relationships between clinical isolates and reference strains. The method was used to determine the genotypes of C. trachomatis in 237 positive urogenital and/or urine specimens collected at a Swedish sexually transmitted disease clinic during 1 year. The most common genotypes corresponded to serotypes E (47%) and F (17%). The omp1 gene was highly conserved for genotype E (106 of 112 samples without any mutation) and F (41 of 42 samples without any mutation) strains but appear slightly less conserved for genotypes G (n = 6) and H (n = 6), where the sequences displayed one to four nucleotide substitutions relative to the reference sequence. Genotyping of samples collected at the follow-up visit indicated that two patients had become reinfected, while three other patients suffered treatment failure or reinfection. One woman appeared to have a mixed infection with two different C. trachomatis strains. This omp1 genotyping method had a high reproducibility and could be used for epidemiological characterization of sexually transmitted Chlamydia infections.

Chlamydia and Chlamydiales: more than meets the eye

This review summarizes the dramatic changes that have occurred in the taxonomy of bacteria known as Chlamydia. Best known for the diseases they cause in humans, these intracellular bacteria also comprise many species that are responsible for a wide variety of clinically and economically important diseases in livestock and companion animals. The old taxonomy grouped most of these species into C. psittaci because systematic methods for routinely distinguishing them were not available. DNA-based testing methods are now available that distinguish different chlamydial families, genera, and species. This summary reviews these tests and a number of oligonucleotide primers that distinguish these groups using PCR and PCR-RFLP. DNA-based methods are also being used to discover new families of chlamydia-like bacteria, at least one of which is responsible for abortion in cattle (Waddlia chondrophila). This review summarizes the pathogenic roles of the Chlamydiaceae, new families, and individual species within the order Chlamydiales. These discoveries create opportunities for veterinarians to carry out epidemiological studies of chlamydiae that previously were not possible.