Background We sought to determine if the population increases in neurosyphilis cases in British Columbia, Canada were attributable to early (infectious) versus late (tertiary) syphilis stage of diagnosis by examining concordance of trends in syphilis by stage of disease and neurosyphilis diagnosis.

Methods Data were extracted from the provincial STD database that includes all syphilis diagnosis in British Columbia through a centralised programme, and where diagnoses are confirmed by physicians with syphilis expertise. Early syphilis was defined as either secondary (rash or mucous lesions), or early latent syphilis (asymptomatic with a negative or lower RPR titre within the previous year). Late latent syphilis and tertiary neurosyphilis diagnoses were defined by laboratory and clinical interpretation by experienced physicians. We excluded primary syphilis for this analysis since neurosyphilis does not occur during this stage. Trends in syphilis by stage and diagnosis were compared.

Results Overall rates of syphilis diagnosis increased from 2.0/100,000 in 1993 to 10.1/100,000 in 2012. Early syphilis increased over the same time period from 0.4/100,000 to 6.4/100,000 and neurosyphilis diagnoses increased from 0.03/100,000 (1 case) in 1993 to 0.8/100,000 (35 cases) in 2012. There was a major recent fluctuation in early syphilis diagnosis, with a 56% decline in 2009 –2010, followed by a 231% increase in 2011 – 2012. At the same time, a similar pattern of neurosyphilis diagnoses trends occurred, with a 65% decline in 2009/10 and 225% rise in 2011/12. In contrast, while late syphilis fluctuated modestly over this time period it remained generally stable (Range 1.3 – 2.9/100,000 with minimal increase).

Conclusion Neurosyphilis diagnoses generally mirrored early (infectious) syphilis rates at the population level, suggesting the majority of neurosyphilis in this epidemic occur during early rather than late stage infection. This has important implications on education and management strategies for syphilis control programmes.