The invisible influence: impact of psychological mechanisms of sexual behaviour on chlamydia transmission

Chlamydia is a sexually transmitted infection (STI) and can cause long-term complications, such as subfertility. Therefore, prevention of chlamydia is important, for example through condom use. Whether people use condoms depends on psychological characteristics, such as risk perception. Mathematical models are often used to predict chlamydia transmission. Psychological characteristics and changes in these characteristics over time are rarely incorporated into mathematical models. Therefore, a study named "Mathematical models incorporating Psychological determinants: control of Chlamydia Transmission" (iMPaCT) " was conducted. Data on sexual behaviour, psychological characteristics and STI diagnoses of heterosexual men and women between 18 and 24 years old, who visited a Sexual Health Center (SHC) was collected at four time points in a year. Psychological characteristics, including self-efficacy (confidence in one's ability to use condoms), social norms (assessment of what others do or think you should do), attitudes (views towards condom use), intentions (plans to use condoms) and impulsivity (degree of control over behaviour) were found to distinguish different subgroups. These characteristics allow identification of people who are at higher risk for chlamydia or for whom behavioural change is more difficult to achieve. Combining epidemiology, behavioural sciences and mathematical modelling resulted in a more accurate assessment of chlamydia risk. In addition, model results showed that behavioural interventions, such as promoting condom use, tailored to psychological characteristics of subgroups can reduce chlamydia transmission. This provides valuable information to improve chlamydia prevention at the SHC.