Self-reported sexually transmitted infections among adolescents and adults in Zambia and Zimbabwe: evidence from Demographic and Health Surveys, 2005-2018

Objectives
Globally, curable sexually transmitted infections (STIs) are increasing, particularly in sub-Saharan Africa, yet epidemiological data remain limited, hindering progress towards the 2030 global STI targets. This study assessed the prevalence of self-reported STIs in the last 12 months among adolescent girls and women (AGW) and adolescent boys and men (ABM) aged 15–59 who ever had sex in Zambia and Zimbabwe at three time points. It also assessed whether observed changes across survey rounds persisted after adjusting for sociodemographic and sexual behaviour characteristics.

Design
We analysed six rounds of Demographic and Health Surveys, three per country, collected between 2005 and 2018, using descriptive statistics and logistic regression, while accounting for survey design.

Setting
Zambia and Zimbabwe.

Participants
A total weighted sample of 86 366 AGW and ABM was included in the study.

Outcome measure
Self-reported STIs in the last 12 months.

Results
Overall, self-reported STI prevalence was higher in Zimbabwe than Zambia. Among Zambian ABM, self-reported STIs increased from 6.2% in 2007 to 7.1% in 2018 (adjOR=1.28, 95% CI 1.05 to 1.57, p=0.005). Among Zimbabwean AGW, prevalence decreased from 11.7% in 2005/2006 to 8.3% in 2015 (adjOR=0.72, 95% CI 0.61 to 0.85, p<0.001). No significant differences between survey rounds were observed among AGW in Zambia (2007: 5.2%, 2018: 5.1%, adjOR=1.01, 95% CI 0.83 to 1.22, p=0.070) and ABM in Zimbabwe (2005/2006: 7.9%, 2015: 8.4%; adjOR=1.13, 95% CI 0.92 to 1.38, p=0.371). Self-reported STIs were associated with marital status, HIV status and number of sexual partners in the last 12 months among ABM and AGW. Among ABM, self-reported STIs decreased with older age at sexual debut. In Zimbabwe, lower educational attainment and wealth were also associated with higher STI prevalence.

Conclusion
These findings highlight differences in STI prevalence by sex and country across survey rounds, underscoring the need for tailored STI prevention, diagnostic and treatment strategies, particularly for high-risk groups.