Improving the detection of congenital syphilis: reviewing test utility and adherence to recommendations

Western Australia (WA) has experienced a resurgence of congenital syphilis. Appropriate microbiology testing of the neonate is recommended to confirm infection, including syphilis immunoglobulin M (IgM), rapid plasma reagin (RPR) paired with a maternal sample, and polymerase chain reaction (PCR) on placenta and nasal swabs. We examined the performance of microbiology tests in confirmed congenital syphilis cases and the adherence to testing recommendations in those assessed as high risk. We reviewed the microbiology results of confirmed congenital syphilis cases in WA between 1 January 2018 and 31 December 2023. In addition, microbiology testing of neonates from metropolitan Perth identified as being at a high risk of congenital syphilis between 1 January 2021 and 31 October 2023 was reviewed. Eighteen congenital syphilis cases were identified; data were unavailable for a case born interstate. Of the 17 included cases, the case fatality rate was 35% (6/17; five stillbirths and one perinatal death). Placenta tissue PCR was positive in all stillbirths. Of the 12 live births, 83% were symptomatic at delivery. Perinatal testing was performed in 11 live births (11/12); IgM was detected in 55% (6/11). Placenta tissue PCR was positive in 88% (7/8 tested). Nasal swab PCR was positive in 57% (4/7 tested). There were 22 neonates classified as being at a high risk for congenital syphilis infection; all had IgM and RPR testing. Syphilis PCR was performed on placenta tissue samples in 64% (14/22) and on nasal swabs in 64% (14/22) of cases. Comprehensive microbiological testing, including syphilis IgM and placenta tissue PCR, is required to confirm congenital syphilis infection. Continuous evaluation of testing will be crucial for individual case detection and monitoring of the ongoing outbreak. Given the risk of incomplete specimen collection, our data support ​the adoption of a risk-based approach for neonates at risk of congenital syphilis, with management guided by maternal serology and treatment history.