Background: Rates of congenital syphilis (CS) have increased in the United States since 2013. Although treatment during pregnancy may effectively prevent CS, surveillance cases have been reported where the infant has evidence of infection despite their birthing parent receiving adequate therapy. To inform prevention efforts, we reviewed characteristics of these “breakthrough” surveillance cases.
Methods: We reviewed cases of CS reported through the National Notifiable Diseases Surveillance System during 2016–2020. We categorized liveborn infants as a potential breakthrough case if the birthing parent was documented to have received treatment appropriate for their stage of infection initiated ≥30 days before delivery, without evidence of reinfection, and the infant displayed clinical or laboratory findings included in the current Council of State and Territorial Epidemiologists’ case definition.
Results: During 2016–2020, there were 6,927 CS cases reported, of which 287 cases (4.1%) were classified as potential breakthrough cases, representing stable morbidity over time (4.8% in 2016, 4.5% in 2020). Cases in non-Hispanic American Indian/Alaskan Native birthing parents had a higher proportion classified as breakthrough (8.5%) than non-Hispanic Black (5.1%), non-Hispanic White (4.3%) or Hispanic birthing parents (2.9%).
CS was confirmed in six (2.1%) cases by darkfield microscopy. A further 67 cases met the CS definition by findings highly indicative of infection: reactive cerebrospinal fluid Venereal Disease Reference Laboratory testing (21 cases; 7.3%), radiographic long bone changes (41; 14.3%), or both (5 cases; 1.7%)
The remaining cases were reported with less-specific signs: elevated CSF white blood cell count or protein (146, 50.9%), other clinical findings (e.g., hepatosplenomegaly) (33, 11.5%) or both (35, 12.2%). Of the 33 cases with only other clinical findings, 26 (78.8%) had only jaundice and/or hepatitis reported.
Conclusion: Breakthrough cases represent a threat to CS elimination, as they have not been prevented by recommended public health interventions. The six cases confirmed by darkfield microscopy may represent breakthrough infections, or inaccurate birthing parent treatment data. Potential breakthrough cases that met the surveillance case definition through less-specific criteria (CSF cell counts, protein, and jaundice/hepatitis) may demonstrate an overly sensitive case definition. Further work is required to ascertain the validity of reported breakthrough cases.
