How consistent are antenatal HIV and syphilis results across data sources?
Syphilis is a curable sexually transmitted infection (STI) caused by the bacterium Treponema pallidum (TP). Globally, about 7.1 million people were newly infected with TP and an estimated 200 000 deaths were due to syphilis in 2020.
Syphilis can be transmitted from mother to child during pregnancy and childbirth. In pregnant women, TP can cause miscarriage, stillbirth, or early neonatal death as well as congenital infection in the baby. Babies born with congenital syphilis can have bone damage, severe anaemia, enlarged liver and spleen, jaundice, neurological conditions including blindness or deafness, meningitis, or skin rashes.
South Africa has a high burden of syphilis. In 2023, there were an estimated 1 739 congenital syphilis cases reported to the National Institute for Communicable Diseases (NICD), a division of the National Health Laboratory Service, up from 373 cases reported in 2020. These data from South Africa suggest increased transmission within communities.
South Africa reports high antenatal syphilis testing coverage, with the 2022 antenatal care human immunodeficiency virus (HIV) sentinel survey estimating 97.5%. Yet, delays in results and treatment remain, with the congenital syphilis case rate was still 198 per 100 000 live births in 2023. Recent guideline updates introduced rapid dual HIV/syphilis testing, more frequent screening, and clearer treatment protocols, but data to track progress toward elimination remain limited.
The antenatal care HIV sentinel surveillance system has long monitored HIV and syphilis, but while HIV testing from routine data has been validated, syphilis testing has not.
To address this gap, we assessed agreement between routine medical record data and reference laboratory testing, and compared syphilis prevalence by documentation status.
Materials and Methods
The 2022 ANC survey collected information on participant demographic characteristics, antenatal visits, and gestational age. The most recent syphilis test result was abstracted from participants’ medical records, and blood specimens were collected for HIV testing. Remnant specimens from the survey were stored at the NICD. The syphilis results abstracted from medical records were from syphilis testing performed at each participant’s first ANC visit and around 32–34 weeks’ gestation as per national guidelines at the time.
In the present study, we tested 700 randomly selected stored specimens for syphilis in the reference laboratory using a syphilis rapid diagnostic test (RDT) followed by confirmatory RPR testing on all positive samples. We assessed the agreement between the most recent syphilis test results extracted from medical records and the result of the syphilis testing performed in the reference laboratory.
Results
Among 431 women who had syphilis results available from both medical records and reference laboratory testing, the overall percentage agreement in syphilis test results extracted from medical records and reference laboratory-based syphilis testing was 96.76% (95% CI: 94.60-98.07%), and the associated kappa score was 57.16% (p<0.001).
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