Reasons for the sharp increase of genital chlamydia infections reported in the first months of 2007 in Sweden

Chlamydial and Gonococcal Genital Infections: A Narrative Review

Sexually transmitted infections (STIs) constitute one of the leading causes of disease burden worldwide, leading to considerable morbidity, mortality, health expenditures, and stigma. Of note are the most common bacterial STIs, chlamydial and gonococcal infections, whose etiological agents are Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG), respectively. Despite being usually asymptomatic, in some cases these infections can be associated with long-term severe complications, such as pelvic inflammatory disease, chronic pelvic pain, infertility, ectopic pregnancy, and increased risk of other STIs acquisition. As the symptoms, when present, are usually similar in both infections, and in most of the cases these infections co-occur, the dual-test strategy, searching for both pathogens, should be preferred. In line with this, herein we focus on the main aspects of CT and NG infections, the clinical symptoms as well as the appropriate state-of-the-art diagnostic tests and treatment. Cost-effective strategies for controlling CT and NG infections worldwide are addressed. The treatment for both infections is based on antibiotics. However, the continuing global rise in the incidence of these infections, concomitantly with the increased risk of antibiotics resistance, leads to difficulties in their control, particularly in the case of NG infections. We also discuss the potential mechanism of tumorigenesis related to CT infections. The molecular bases of CT and NG infections are addressed, as they should provide clues for control or eradication, through the development of new drugs and/or effective vaccines against these pathogens.

Changes in the Trend of Sexually Acquired Chlamydia Infections in Sweden and the Role of Testing: A Time Series Analysis

BACKGROUND

We investigated the notification trends of sexually acquired chlamydia (chlamydia) and its association with testing in Sweden before (1992-2004) and after (2009-2018) the discovery of a new variant of Chlamydia trachomatis (nvCT).

METHODS

We applied monthly time series analysis to study chlamydia trends and annual time series to study chlamydia rates adjusted for testing. We analyzed incidence nationally and by county group (based on able and unable to detect nvCT at time of discovery).

RESULTS

We present data on 606,000 cases of chlamydia and 9.9 million persons tested. We found a U-shaped chlamydia trend during the period 1992-2004, with an overall increase of 83.7% from 1996 onward. The period 2009-2018 began with a stable trend at a high incidence level followed by a decrease of 19.7% during the period 2015-2018. Peaks were seen in autumn and through during winter and summer. Similar results were observed by groups of county, although with varying levels of increase and decrease in both periods. Furthermore, increased testing volume was associated with increased chlamydia rates during the first period (P = 0.019) but not the second period.

CONCLUSIONS

Our results showed that chlamydia trends during the period 2009-2018 were not driven by testing, as they were during the period 1992-2004. This suggests less biased notified chlamydia rates and thus possibly a true decrease in chlamydia incidence rates. It is important to adjust case rates for testing intensity, and future research should target other potential factors influencing chlamydia rates.

Rise and fall of the new variant of Chlamydia trachomatis in Sweden: mathematical modelling study

Objectives

A new variant of Chlamydia trachomatis (nvCT) was discovered in Sweden in 2006. The nvCT has a plasmid deletion, which escaped detection by two nucleic acid amplification tests (Abbott-Roche, AR), which were used in 14 of 21 Swedish counties. The objectives of this study were to assess when and where nvCT emerged in Sweden, the proportion of nvCT in each county and the role of a potential fitness difference between nvCT and co-circulating wild-type strains (wtCT).

Methods

We used a compartmental mathematical model describing the spatial and temporal spread of nvCT and wtCT. We parameterised the model using sexual behaviour data and Swedish spatial and demographic data. We used Bayesian inference to fit the model to surveillance data about reported diagnoses of chlamydia infection in each county and data from four counties that assessed the proportion of nvCT in multiple years.

Results

Model results indicated that nvCT emerged in central Sweden (Dalarna, Gävleborg, Västernorrland), reaching a proportion of 1% of prevalent CT infections in late 2002 or early 2003. The diagnostic selective advantage enabled rapid spread of nvCT in the presence of high treatment rates. After detection, the proportion of nvCT decreased from 30%–70% in AR counties and 5%–20% in counties that Becton Dickinson tests, to around 5% in 2015 in all counties. The decrease in nvCT was consistent with an estimated fitness cost of around 5% in transmissibility or 17% reduction in infectious duration.

Conclusions

We reconstructed the course of a natural experiment in which a mutant strain of C. trachomatis spread across Sweden. Our modelling study provides support, for the first time, of a reduced transmissibility or infectious duration of nvCT. This mathematical model improved our understanding of the first nvCT epidemic in Sweden and can be adapted to investigate the impact of future diagnostic escape mutants.

The Swedish new variant of Chlamydia trachomatis

PURPOSE OF REVIEW

This review focuses on the anatomy of the Swedish new variant of Chlamydia trachomatis (nvCT). This information provides an interesting insight into the emergence of new strains (how, where, and when), and the important lessons learned are discussed.

RECENT FINDINGS

In late 2006, the nvCT was first reported in Sweden; it carries a 377 bp deletion within its plasmid which covers the single targets originally used by Roche and Abbott diagnostic systems. The nvCT spread rapidly with thousands of falsely negative diagnoses. Genome sequencing and phenotypic characterization showed that the biological fitness of nvCT when compared with wild-type CT in vitro is unaltered. Therefore, the rapid transmission of nvCT was due to the selective advantage gained from failed diagnosis and the introduction of nvCT into a high-frequency transmitting population. The proportions of nvCT cases are now converging toward equilibrium with the wild-type CT strains. Interestingly, the nvCT remains rarely reported beyond the Nordic countries.

SUMMARY

The spread of nvCT had a substantial impact on C. trachomatis identification, epidemiology, and public health in Sweden. Lessons learned from this experience include the importance of investigating the incidence and epidemiology of infection in detail, the frequent participation in appropriate quality assurance schemes, and the careful design of diagnostic assays. The nvCT presents a unique opportunity to study the spread of a single C. trachomatis strain within both the human and bacterial populations; this may substantially increase our knowledge of epidemiology and transmission of chlamydial infections, and other sexually transmitted infections.

Protective immunity to Chlamydia trachomatis genital infection: evidence from human studies

Background. Some screening and treatment programs implemented to control Chlamydia trachomatis genital infections and their complications have shown initial reductions in infection prevalence, followed by increases to preprogram levels or higher. One hypothesis is that treatment shortens duration of infection, attenuates development of protective immunity, and thereby, increases risk of reinfection. Methods. A literature review was undertaken to assess evidence supporting the concept of protective immunity,its characteristics, and its laboratory correlates in human chlamydial infection. The discussion is organized around key questions formulated in preparation for the Chlamydia Immunology and Control Expert Advisory Meeting held by the Centers for Disease Control and Prevention in April 2008. Results. Definitive human studies are not available, but cross-sectional studies show that chlamydia prevalence,organism load, and concordance rates in couples decrease with age, and organism load is lower in those with repeat infections, supporting the concept of protective immunity. The protection appears partial and can be overcome after reexposure, similar to what has been found in rodent models of genital infection. No data are available to define the duration of infection required to confer a degree of immunity or the time course of immunity after resolution of untreated infection. In longitudinal studies involving African sex workers, a group presumed to have frequent and ongoing exposure to chlamydial infection, interferon-g production by peripheral blood mononuclear cells in response to chlamydial heat-shock protein 60 was associated with low risk of incident infection.In cross-sectional studies, relevant T helper 1-type responses were found in infected persons, paralleling the studies in animal models. Conclusions. The data support the concept that some degree of protective immunity against reinfection develops after human genital infection, although it appears, at best, to be partial. It is likely that factors besides population levels of immunity contribute to trends in prevalence observed in screening and treatment programs.Future studies of protective immunity in humans will require longitudinal follow-up of individuals and populations,frequent biological and behavioral sampling, and special cohorts to help control for exposure.

The Swedish new variant of Chlamydia trachomatis: genome sequence, morphology, cell tropism and phenotypic characterization

Chlamydia trachomatis is a major cause of bacterial sexually transmitted infections worldwide. In 2006, a new variant of C. trachomatis (nvCT), carrying a 377 bp deletion within the plasmid, was reported in Sweden. This deletion included the targets used by the commercial diagnostic systems from Roche and Abbott. The nvCT is clonal (serovar/genovar E) and it spread rapidly in Sweden, undiagnosed by these systems. The degree of spread may also indicate an increased biological fitness of nvCT. The aims of this study were to describe the genome of nvCT, to compare the nvCT genome to all available C. trachomatis genome sequences and to investigate the biological properties of nvCT. An early nvCT isolate (Sweden2) was analysed by genome sequencing, growth kinetics, microscopy, cell tropism assay and antimicrobial susceptibility testing. It was compared with relevant C. trachomatis isolates, including a similar serovar E C. trachomatis wild-type strain that circulated in Sweden prior to the initially undetected expansion of nvCT. The nvCT genome does not contain any major genetic polymorphisms - the genes for central metabolism, development cycle and virulence are conserved - or phenotypic characteristics that indicate any altered biological fitness. This is supported by the observations that the nvCT and wild-type C. trachomatis infections are very similar in terms of epidemiological distribution, and that differences in clinical signs are only described, in one study, in women. In conclusion, the nvCT does not appear to have any altered biological fitness. Therefore, the rapid transmission of nvCT in Sweden was due to the strong diagnostic selective advantage and its introduction into a high-frequency transmitting population.

Repeat infection with Chlamydia trachomatis: a prospective cohort study from an STI-clinic in Stockholm

Background

Infection with genital Chlamydia trachomatis (Ct) is the most common notifiable sexually transmitted infection (STI) in Sweden. A mutated Chlamydia, nvCT, has contributed to the increase. The occurrence of repeat infections is not investigated in Sweden. The current paper presents the study protocol for the first Swedish clinical investigation of repeat Chlamydial infection. The concern of the study is whether a Chlamydia infection at inclusion indicates an increased risk for Chlamydia at follow-up after 6–8 months, gender-specific risk factors for and clinical presentation of repeat infections.

Methods and design

Sesam City is a drop-in clinic in the city centre of Stockholm. Patients 20 years and older are admitted. During 2007, the clinic had 15 000 visits, 60% made by men. In December 2007, a cohort study began, and data collection was finished in April 2009. A total of 2813 study participants aged 20–39 years were recruited. Data collection included an anonymous self-administered paper-and-pen questionnaire on sexual behaviour, reproductive health and history of Chlamydia, and condom use. Chlamydia tests were performed by self-sampled specimens, analyzed by the ProbeTec (Becton Dickinson) method, Ct-positive specimens also analyzed with a nvCT-specific method. Data from medical records were summarized in clinical report forms. Patients positive for Chlamydia were retested 4 weeks after treatment. Contact tracing covered sexual contacts during the last 12 months. At follow-up 6–8 months after inclusion, Chlamydia tests were performed, and a new questionnaire and CRF completed.

Discussion

A STI-clinic-based prospective cohort study allowed us to survey 2813 adult patients. The collected data will provide gender-specific information on the occurrence of and risk for repeat Chlamydia infection, the occurrence of nvCT, and clinical data and information on sexual behaviour and reproductive health, risk-taking and condom use.

Emergence and spread of Chlamydia trachomatis variant, Sweden

A variant of Chlamydia trachomatis that had escaped detection by commonly used systems was discovered in Sweden in 2006. In a nationwide study, we found that it is now prevalent across Sweden, irrespective of the detection system used. Genetic analysis by multilocus sequence typing identified a predominant variant, suggesting recent emergence.