Modelling the impact of tailored behavioural interventions on chlamydia transmission

Abstract

Behavioural interventions tailored to psychological characteristics of an individual can effectively achieve risk-reducing behaviour. The impact of tailored interventions on population-level chlamydia prevalence is unknown. We aimed to assess the impact on overall chlamydia prevalence five years after the introduction of an intervention aimed at increasing self-efficacy, social norms, attitudes and intentions towards condom use (i.e., condom intervention), and an intervention aimed at increasing health goals and decreasing impulsiveness (i.e., impulsiveness intervention). A pair model, informed by longitudinal psychological and behavioural data of young heterosexuals visiting sexual health centers, with susceptible-infected-susceptible structure was developed. The intervention effect was defined as an increased proportion of each subgroup moving to the desired subgroup (i.e., lower risk subgroup). Interventions tailored to subgroup-specific characteristics, assuming differential intervention effects in each subgroup, more effectively reduced overall chlamydia prevalence compared to non-tailored interventions. The most effective intervention was the tailored condom intervention, which was assumed to result in a relative reduction in chlamydia prevalence of 18% versus 12% in the non-tailored scenario. Thus, it is important to assess multiple psychological and behavioural characteristics of individuals. Tailored interventions may be more successful in achieving risk-reducing behaviour, and consequently, reduce chlamydia prevalence more effectively.

Figure 1

In the left panel (a), the impact of introducing condom promotion at SHC, an impulsiveness intervention at SHC, and condom promotion campaign, assuming a non-differential (ND) intervention effect (solid lines), and a differential (D) intervention effect (dashed lines) on overall chlamydia prevalence for five consecutive years is shown. On the right panel (b), the impact of introducing condom promotion at SHC, and an impulsiveness intervention at SHC with differential intervention effects, assuming that only individuals who were diagnosed with chlamydia were targeted (CT + , dash-dotted lines), and that only individuals who tested chlamydia negative were targeted (CT−, dotted lines), on overall chlamydia prevalence for five consecutive years is shown. Note that the y-axis starts at 10% to better visualize the differences between the interventions.

Figure 2

Impact on chlamydia prevalence five years after the introduction of condom promotion at SHC (a), and of the impulsiveness intervention at SHC (b) with differential intervention effects, targeted at only at individuals who tested chlamydia positive (CT +), only at individuals who tested chlamydia negative (CT−), and targeted at all tested (All).

Figure 3

Uncertainty analyses mixing parameter. Impact on overall chlamydia prevalence five years after the introduction of condom promotion at SHC (a–c), impulsiveness intervention at SHC (d–f), targeted at only at individuals who tested chlamydia positive (CT +), only at individuals who tested chlamydia negative (CT−), and targeted at all tested (All), and the condom promotion campaign (g), for different values of the mixing parameter. CT Chlamydia trachomatis, CT+  Chlamydia trachomatis positive; CT− Chlamydia trachomatis negative, RD relative difference.

Figure 4

Uncertainty analyses intervention effect. Impact on overall chlamydia prevalence five years after the introduction of condom promotion at SHC (a–c), impulsiveness intervention at SHC (d–f), targeted at only at individuals who tested chlamydia positive (CT+), only at individuals who tested chlamydia negative (CT−), and targeted at all tested (All), and the condom promotion campaign (g), for assuming no differential intervention effect, differential intervention effect, partially differential intervention effect, and alternate differential intervention effect. CT Chlamydia trachomatis, CT+  Chlamydia trachomatis positive; CT− Chlamydia trachomatis negative, RD relative difference.