The effect of STI screening during pregnancy on vertical transmission of HIV and adverse pregnancy outcomes in South Africa: a modelling study

Abstract

Introduction: Sexually transmitted infections (STIs) in pregnancy are associated with an increased risk of vertical HIV transmission and adverse pregnancy and birth outcomes. In South Africa, syndromic management is the standard of care for STI management. We assessed the potential impact of point-of-care (POC) screening for curable STIs (Chlamydia trachomatis [CT], Trichomonas vaginalis [TV] and Neisseria gonorrhoeae [NG]) during pregnancy on vertical HIV transmission and adverse pregnancy and birth outcomes.

Method: We developed a static mathematical model to estimate the impact of syndromic management compared to POC screening of STIs in pregnant women attending antenatal clinics in South Africa over one calendar year (2022). Our model assumptions regarding the effect of CT, NG and TV on adverse pregnancy/birth outcomes and vertical HIV transmission were informed by two separate meta-analyses that we conducted. Local studies informed estimates of STI prevalence, POC screening uptake and treatment, and sensitivity of syndromic management.

Results: In the absence of POC screening for curable STIs, 25.5% of pregnant women without HIV and 34.6% of pregnant women living with HIV were estimated to have undiagnosed and untreated STIs. In the POC scenario, 92% (95% CI: 85-100%) of STIs were diagnosed and treated during pregnancy, reducing antenatal maternal HIV incidence by 10.0% (95% CI: 1.0-20.1%). Overall, vertical HIV transmission was anticipated to reduce by 8.6% (5.2-13.8%), with reductions of 20.9% (15.2-27.0%) at birth and 2.5% (-0.9% to 9.0%) postnatally, in the POC screening scenario compared to current syndromic management. POC screening of curable STIs is further estimated to reduce the incidence of stillbirth by 10.1% (1.3-18.7%), preterm delivery by 6.3% (3.4-9.7%), infants born small for gestational age by 2.7% (0.7-4.9%) and low birth weight by 9.1% (0.9-18%).

Conclusions: POC STI screening and treatment may modestly reduce maternal HIV incidence, vertical HIV transmission, and the risk of adverse pregnancy and birth outcomes, and would substantially reduce the burden of curable STIs in pregnancy. The study provides evidence to move beyond the syndromic management of STIs in South Africa, particularly in antenatal care.

Keywords: Chlamydia trachomatis; Neisseria gonorrhoeae; STI screening; South Africa; Trichomonas vaginalis; vertical HIV transmission.

Figure 1

Impact of POC screening of curable STIs in antenatal care on vertical transmission of HIV. Bars represent the percent reduction for each outcome with lower and upper error bars representing confidence intervals. Abbreviations: ANC, antenatal clinic; POC, point‐of‐care; STIs, sexually transmitted infections.

Figure 2

Sensitivity analysis of the impact of POC STI screening in ANC on vertical transmission of HIV. The horizontal bold line represents a reduction in total vertical HIV transmission (8.6%). Abbreviations: ANC, antenatal clinic; POC, point‐of‐care; STIs, sexually transmitted infections; WLHIV, women living with HIV.

Figure 3

Sensitivity analysis of the impact of POC STI screening in ANC on adverse birth outcomes. Lower and upper error bars are calculated using the 95% confidence interval limits for the odds ratio for the STI‐adverse pregnancy outcome association. Abbreviations: LBW, low birthweight; POC, point‐of‐care; PTD, preterm delivery; SGA, small for gestational age; STIs, sexually transmitted infections.

Figure 4

Effect of POC screening and treatment of curable STIs during pregnancy. The dotted lines show the risk ratio of 1. Lower and upper error bars represent the 95% confidence intervals for each outcome. Abbreviations: POC, point‐of‐care; STIs, sexually transmitted infections.