Table 1

Sensitivity analysis—effect of varying (selected) assumptions and values, on national prevalence estimates for adults aged 15–49 years at years 2000 and 2016: (a) syphilis; (b) gonorrhoea

ParameterDefault valueAlternative assumptionPrevalence Zimbabwe, women, at 2000→2016Prevalence Morocco,
women,at 2000→2016
(a) Syphilis
Default best syphilis prevalence estimates1.94→1.54%1.48%→0.55%
Diagnostic test performance, relative to RPR-positive plus TPHA-positive (dual positivity) as ‘gold standard’
 TPHA in ANC or FP population0.80.61.0Lower value: 1.73→1.58%
Upper value: 2.11→1.49%
Lower value: 1.45→0.36%
Upper value: 1.57→0.74%
 RPR0.60.451.0Lower value: 1.99→1.38%
Upper value: 1.84→1.99%
Lower value: 1.22→0.58%
Upper value: 2.27→0.46%
 Rapid syphilis test (TPHA-based)0.70.551.0Lower value: 1.90→1.34%
Upper value: 1.96→1.96%
Not used
(b) Gonorrhoea
Default best gonorrhoea prevalence estimates2.5→3.8%0.60→0.36%
 Diagnostic test performance—gonorrhoea
  Specificity PCR and LCR for gonorrhoea, women, genital fluid99.7%99.0%100%Lower value: 2.3→3.6%
Upper value: 2.7→4.0%
Lower value: 0.28→0.11%
Upper value: 0.67→0.55%
  Specificity PCR, LCR and SDA for gonorrhoea, women, urine99.7%99.0%100%Lower value: 2.3→3.7%
Upper value: 2.7→4.0%
Lower value:0.16→0.09%
Upper value:0.82→0.44%
  Specificity PCR, LCR and SDA for gonorrhoea, women, urine and genital fluid99.799.0%100%Lower value: 2.1→3.6%
Upper value: 2.8→4.1%
Lower value: 0.11→0.05%
Upper value:0.88→0.64%
  Sensitivity of PCR/LCR and SDA for gonorrhoea, women, urine and genital fluid93.3%; 91.6%; 91.6%80%100%Lower value: 2.8→4.3%
Upper value: 2.4→3.6%
Lower value:0.67→0.41%
Upper value:0.54→0.32%
  Sensitivity of culture for gonorrhoea, women75.7%50%90%Lower value: 2.7→4.1%
Upper value: 2.6→3.8%
Not used
 Other parameters in the gonorrhoea prevalence estimation 
  Weight of UD case report data points, relative to national prevalence studies (the latter at 100%)25%1%50%Not usedLower value: 0.70→0.26%
Upper value: 0.54→0.37%
  Weight of neighbouring country prevalence surveys, relative to national prevalence studies10%0%30%Lower value: 2.2→2.5%
Upper value: 3.1→4.5%
Lower value: 0.43→0.31%
Upper value:0.82→0.43%
  Annual dilution factor in moving average estimation for gonorrhoea*20%0%40%Lower value: 3.0% constant
Upper value: 2.4→6.0%
Lower value: 0.49% constant
Upper value: 0.67→0.37%
  • *The annual dilution factor weights the contribution of each data point to the estimation for other years than the study year (earlier and later, within the period from first to last data point) downward, by a fixed proportion (default value: 20%) for each additional year away from the estimated year.

  • ANC, antenatal care; FP, family planning; LCR, ligase chain reaction; RPR, rapid plasma reagin; SDA, strand displacement amplification; TPHA, Treponema pallidum haemagglutination assay; UD, urethral discharge.