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Background: Neurologic involvement (neurosyphilis, (NS)) can occur at any stage of syphilis infection, and can lead to serious disability. The CDC case definition for NS requires cerebrospinal fluid (CSF) examination. Syphilis cases with neurologic symptoms that have been diagnosed and treated as NS, but lack a CSF examination, are reported to CDC without indication of NS. The NS case definition may exclude cases important for identifying epidemiologic changes of NS.
Methods: Among syphilis cases diagnosed during 2014-2015 in New York City, we identified those suspected of having NS that did not meet the case definition (“suspect NS”). Suspect NS was defined as incident syphilis with 1) treatment consistent with NS, and 2) documented neurologic symptoms, or, provider diagnosis of NS. We calculated the percent change in NS cases that would result if suspect cases were counted, and compared syphilis stage, neurologic symptoms (including ocular), sex, HIV status, sex of sex partners, and median age of suspect to confirmed/probable cases.
Results: NYC reported 11,589 cases of syphilis (any stage); 32 (0.3%) met the case definition for confirmed NS, and 20 for probable NS (0.2%). Nine cases (0.07%) met our definition of suspect NS; adding them to the confirmed/probable cases would result in a 17.3% increase in NS cases over the 2 year period. Suspect cases were significantly more likely than confirmed/probable cases to have been staged as early latent syphilis (44% vs 14%, p=.047) and to have ocular symptoms (67% vs 21%, p=.011).
Conclusions: The CDC case definition may undercount cases of this potentially serious condition. Most suspect NS cases in NYC had relatively recent syphilis infection. Most had ocular symptoms; counting them as NS could impact measures of the burden of ocular syphilis. Examination of all syphilis cases with neurologic symptoms could inform about the possible changing epidemiology of NS.