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Background: Congenital syphilis (CS) is a devastating yet preventable disease. Standard case definitions are used to ensure jurisdictions use consistent approaches when classifying and reporting cases of notifiable disease. In the late 1980s CDC developed an algorithm (the “old algorithm”) to assist with CS case classification. However, the old algorithm classified cases in a manner that deviated significantly from the case definition. Inconsistent methods of CS classification could affect national trends in reported CS cases. In 2013, CDC released a revised algorithm that aligned with the standard case definition.
Methods: We reviewed all CS investigations conducted among infants born in 2012 in NYC. We evaluated each investigation using the standard case definition as it existed in 2012 as the gold standard, and calculated the sensitivities and specificities of the old and revised algorithm, as well as the classification assigned by NYC.
Results: Among 166 infants investigated for CS, there were no stillbirths or laboratory-confirmed cases. The case definition classified 8/166 (4.8%) as probable cases, while the old algorithm classified 69/166 (41.6%) as probable cases (sensitivity 87.5% (7/8), specificity 60.7% (96/158)). The revised algorithm had a sensitivity and specificity of 100%, while NYC’s case classification had 50% sensitivity (4/8) and 100% specificity (158/158). Four probable cases were missed by NYC, including one that was also missed by the old algorithm.
Conclusions: Applying the CS case definition accurately and consistently is challenging. In NYC, despite using the CS case definition for classification, program staff erroneously classified 50% of probable cases as non-cases. NYC recently convened a workgroup to review policies, procedures, staff training and the process of CS investigations. Other jurisdictions should consider similar efforts to ensure consistent use of the case definition when reporting CS.