The Netherlands Chlamydia Cohort Study: assessing the risk of late complications after Chlamydia trachomatis infection in women

Chlamydia trachomatis (Ct) is a common sexually transmitted infection (STI)
among young people. Although the course of infection is often asymptomatic, Ct
may lead to severe complications in women, such as pelvic inflammatory disease
(PID), prolonged time to pregnancy, ectopic pregnancy, and tubal infertility.
Since various transmission control strategies have not been successful in
reducing Ct prevalence, it may be more effective to focus on prevention of
complications after a Ct infection. Until now, the risk of complications after
Ct has not been assessed directly in a prospective cohort study, but only in
modelling studies. The estimates of complication risk after Ct vary widely
between these studies. Furthermore, factors that contribute to the development
of complications after Ct remain to be elucidated.

The aim of the NEtherlands Chlamydia Cohort STudy (NECCST) is to assess the
risk of developing complications and the time to pregnancy in women with and
without a known previous Ct infection. Furthermore, this study aims at
determining host genetic biomarkers and behavioural, demographic, and pathogen
factors that are associated with the development of these complications.

NECCST is a cohort study and a continuation of the Chlamydia Screening
Implementation (CSI), which was executed between 2008 and 2011 in Rotterdam,
Amsterdam, and South-Limburg, among people between 16 and 29 years of age. In
the CSI, persons were invited to be tested for Ct. Of all participants who gave
informed consent, biological samples have been stored in a Biobank. In NECCST
we will recruit all CSI women who consented to be approached for follow-up
(2,371 CSI Ct positive women and 12,314 CSI Ct negative women), and
prospectively follow them until 2022. Samples stored in the CSI Biobank will be
used to measure the presence of candidate host genetic biomarkers (Single
Nucleotide Polymorphisms (SNPs)). In case the sample is absent or of
insufficient quality, a new sample (buccal swab) will be obtained in 2015.
During NECCST, four data collection moments are foreseen: in 2015, 2017, 2019,
and 2021. Participants will be asked to fill in an online questionnaire at
every data collection moment. In case women report infertility/subfertility in
the questionnaire, medical records will be checked to identify the cause of
their infertility/subfertility. A separate informed consent will be obtained
for this medical record check, after the women have indicated
infertility/subfertility in the questionnaire. At the first and last data
collection moment, participants will also be asked to provide a blood sample at
home (blood drops in a collection tube), in order to measure Immunoglobulin G
(IgG) antibodies for Ct, as a marker of a previous Ct infection.

Participating women will not be subject to any health risk. However,
participants may experience some discomfort by the personal nature of the
questionnaire (e.g. questions on sexual behaviour; however, similar to the ones
they answered during the Chlamydia Screening Implementation), and by the
(self)collection of blood samples at home.