Eurosurveillance - Volume 12, Issue 10, 01 October 2007

Chlamydia trachomatis is the most commonly reported bacterial sexually transmitted infection (STI) in Europe. Genital chlamydial infection causes cervicitis and salpingitis in women and urethritis and conjunctivitis in both men and women.

In 2006, a new variant of Chlamydia trachomatis was reported in Sweden. Three countries – Ireland, Norway, and Denmark – have detected the variant to date, but very few cases in total have occurred. The European network for STI surveillance (ESSTI) and the European Centre for Disease Prevention and Control (ECDC) assessed the potential spread of the variant in other European countries, and concluded that there is currently no evidence that the variant has spread widely across Europe. However, the variant strain has been reported in between 10% and 65% of infected patients in Sweden. It is too early to tell whether the variant will remain confined to Sweden or whether the number of cases will significantly increase. Enhanced surveillance will need to be continued to address these concerns.

After a continuous increase in the reported chlamydia incidence over the past 10 years in Sweden, the incidence decreased by 2% in 2006. A new genetic variant of Chlamydia trachomatis (nvCT) was discovered in Sweden in October 2006 that could not be detected by some of the commonly used diagnostic tests, which led to underreporting of chlamydia cases. This variant has also been called 'swCT' by some authors. After the switch at the end of 2006 to other diagnostic tests that can detect nvCT, the reported incidence rose considerably (75 per 100,000 population) in the beginning of 2007. The objective of this study was to explore alternative explanations for this increase and to propose further action if needed.

A mutant Chlamydia trachomatis variant was detected in Sweden in 2006 and has since also been diagnosed in Norway, but not in Ireland or the Netherlands. This paper describes a study aimed at assessing the presence of the new variant in Denmark. Between November 2006 and April 2007 we tested 3,770 specimens using methods capable of detecting the new variant and distinguishing it from the wild type. In late March 2007 we found one case of the new variant in a 19-year old Danish woman without any known relationship to Sweden. It is surprising that the spread of this sexually transmitted pathogen into Denmark and within Denmark has been so low in view of its rapid and substantial spread within Sweden.

This report describes the actions of public health experts in cooperation with specialists in sexually transmitted diseases (STD), epidemiologists and (molecular) microbiologists to investigate the possible introduction of the swCT variant in the Netherlands:

In 2006, a plasmid deletion mutant of Chlamydia trachomatis was identified in Sweden that can not be detected with those commercial tests targeting the deleted area. In order to study the spread of this strain in France, a laboratory-based surveillance system was set up by the National Reference Centre for Chlamydiae and the Institut de Veille Sanitaire. Among 1,141 C. trachomatis-positive specimens from all over France, the new variant was only detected in one case. This case was a non-French resident consulting a sexually transmitted infections clinic. Although the new variant does not seem to be established in France as yet, surveillance based on the testing of C. trachomatis-positive samples from all over France continues.

Genital Chlamydia trachomatis (GCT) infection is the most common bacterial sexually transmitted infection (STI) in Ireland. A retrospective analysis of 2,087 laboratory-confirmed GCT patient episodes from 2001 to 2006 in the Mid-West of Ireland was undertaken in conjunction with statutorily notifiable data that were reported by the Sexually Transmitted Disease/Genito-Urinary Medicine (STD/GUM) services in the region and used in national surveillance. Data were analysed by year, source, sex and age. The annual incidence of GCT in the Mid-West is increasing. A substantial proportion of GCT infections were diagnosed in the non-STD/GUM setting. The issue of sexually active young people seeking STI screening is a sensitive one, and delays increase the potential for transmission and the possibility of long-term complications when the disease is not treated. Based on this sample, national surveillance would significantly underestimate the burden of disease in Ireland, due to under-reporting. This would have implications for any national chlamydia screening programme. Among those who sought testing, women aged 15 to 19 years are five times more likely to be found positive than men in the same age group. Of those diagnosed in the non-STD/GUM setting, 83% were women. General practitioners and clinicians might consider targeting those aged 15 to 29 years for opportunistic screening and sexual health advice. Contact tracing and follow-up in the non-STD/GUM setting, as well as access for general practitioners to ongoing education on STIs are challenges to be addressed.

Network analysis, tying together sociology and epidemiology, provides a means of looking at the epidemic from a sociogeographic point of view. By highlighting the links between people in sexual networks, it can be useful when designing public health campaigns and carrying out contact tracing.