Investigation of mediating effects of sexual behaviours on the effect of a novel digital intervention on sexually transmitted reinfections: secondary analysis of a randomised controlled trial
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Background
Preventing sexually transmitted re-infections brings health benefits and can be significantly less costly than treating their sequelae. Safetxt is a potential novel digital intervention developed to promote safer sexual behaviours. However, a recent randomised controlled trial of safetxt found no effect on reinfection at 1 year (OR 1.13, 95%CI: 0.98-1.31). We investigated if safetxt’s effect was mediated through sexually risky behaviours.
Methods
We used data from 6248 young people with STIs from 92 UK sexual health clinics. The direct and indirect effects of safetxt on reinfection were estimated using the counterfactual approach. Condom use at last sexual encounter, number of sexual partners and STI testing were assessed as mediators. These were analysed singly and together, using regression models and a formal weighting approach. The assumptions of each approach were considered and tested. Analyses were repeated in the subgroup showing the most promising effect of safetxt: men who have sex with men or with men and women (MSM/MSMW).
Results
No evidence was found for the total, indirect or direct effects differing from the null. Despite not being significant, for MSM/MSMW, some of safetxt’s effect on reducing reinfection was identified as being offset through its effect on number of sexual partners.
Conclusions
There was no evidence that safetxt’s effect on reinfection was mediated through changes in sexually risky behaviours. Adaptations to specifically target these behaviours are unlikely to improve safetxt’s overall effect. However, improving safetxt’s effect on the number of sexual partners a participant has may improve its effect for MSM/MSMW.
What is already known on this topic
The safetxt intervention did not result in a reduction in reinfection rate among 16-24 year olds diagnosed with chlamydia, gonorrhoea or non-specific urethritis in the UK. However, safetxt did result in increased condom use at 1 year. Results of the safetxt trial were most promising for men who have sex with men or with men and women (MSM/MSMW).
What this study adds
Disaggregating the effect of a novel digital intervention on sexually transmitted reinfections allows understanding of the mechanisms through which it acts. Investigators hypothesised that safetxt’s true effect was being mediated through changes in other sexual behaviours. This study shows there is no evidence of this from the safetxt trial.
How this study might affect research, practice or policy
All estimated effects were non-significant. Overall safetxt’s effect in the primary trial analysis was not due to mediation through condom use, number of sexual partners or STI testing. In MSM/MSMW, safetxt’s effect was identified as being reduced through number of sexual partners. Alterations to improve safetxt’s effect on the number of sexual partners a participant has could be considered with the aim of improving its overall effect on reinfection for MSM/MSMW.
