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

Smid, Joost H; Althaus, Christian L; Low, Nicola; Unemo, Magnus; Herrmann, Bjőrn (2020). Rise and fall of the new variant of Chlamydia trachomatis in Sweden: mathematical modelling study. Sexually transmitted infections, 96(5), pp. 375-379. BMJ Publishing Group 10.1136/sextrans-2019-054057

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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).


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.


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.


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.

Item Type:

Journal Article (Original Article)


04 Faculty of Medicine > Pre-clinic Human Medicine > Institute of Social and Preventive Medicine (ISPM)
04 Faculty of Medicine > Faculty Institutions > Teaching Staff, Faculty of Medicine

UniBE Contributor:

Smid, Joost Hubert, Althaus, Christian, Low, Nicola


600 Technology > 610 Medicine & health
300 Social sciences, sociology & anthropology > 360 Social problems & social services




BMJ Publishing Group


[4] Swiss National Science Foundation




Andrea Flükiger-Flückiger

Date Deposited:

28 Oct 2019 15:32

Last Modified:

05 Dec 2022 15:31

Publisher DOI:


PubMed ID:


Uncontrolled Keywords:

Chlamydia trachomatis Sweden basic reproduction number mathematical model nucleic acid amplification test





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