Syphilis prevalence trends in adult women in 132 countries - estimations using the Spectrum Sexually Transmitted Infections model

Abstract

We estimated national-level trends in the prevalence of probable active syphilis in adult women using the Spectrum Sexually Transmitted Infections (STI) model to inform program planning, target-setting, and progress evaluation in STI control. The model fitted smoothed-splines polynomial regressions to data from antenatal clinic surveys and screening and representative household surveys, adjusted for diagnostic test performance and weighted by national coverage. Eligible countries had ≥1 data point from 2010 or later and ≥3 from 2000 or later from adult populations considered representative of the general female population (pregnant women or community-based studies). Between 2012 and 2016, the prevalence of probable active syphilis in women decreased in 54 (41%) of 132 eligible countries; this decrease was substantive (≥10% proportionally, ≥0.10% percentage-point absolute difference and non-overlapping 95% confidence intervals in 2012 and 2016) in 5 countries. Restricting eligible data to prevalence measurements of dual treponemal and non-treponemal testing limited estimates to 85 countries; of these, 45 countries (53%) showed a decrease. These standardized trend estimates highlight the need for increased investment in national syphilis surveillance and control efforts if the World Health Organization target of a 90% reduction in the incidence of syphilis between 2018 and 2030 is to be met.

Figure 1

Average number of eligible syphilis prevalence data points, recorded in the Spectrum STI syphilis database, grouped by WHO region. Note to Fig. 1: Lines represent linear trend lines fitted through the data points for each region.

Figure 2

Spectrum-STI estimations of adult female syphilis prevalence (a) Morocco and (b) Mongolia. Notes to Fig. 2: Data shown are after adjustment for diagnostic test performance. Neither country had any data included from years 1990–1995; both estimations used data from ANC and general populations only; both countries were classified as having a non-substantive prevalence increase over 2012–2016. Solid line = is the best estimate (median of 400 bootstraps), dashed lines are the 95% confidence interval.

Figure 3

Spectrum-estimated national syphilis prevalence in 2016 as a function of estimated prevalence in 2012, and each country’s time trend classification, for 132 countries: (a) Grouped by WHO region. (b) Grouped by time trend category. Notes to Fig. 3: The black dotted line indicates equality of prevalence within a country at 2012 and 2016.

Figure 4

Relation between number of national prevalence data points, and precision of point prevalence estimates. Notes to Fig. 4: Precision expressed, on the y-axis, as the width of the 95% CI (averaged between 2012 & 2016) divided by the point estimate. Each dot represents a country with a Spectrum national trend estimate based on data from ANC and general populations.