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P773 Increased detection rates of primary syphilis by PCR in a provincial laboratory
  1. Prenilla Naidu,
  2. Fiona Ko
  1. Provincial Laboratory for Public Health, Edmonton, Canada


Background North America is experiencing an exponential rise in the numbers of infectious syphilis cases. The United States of America had 9.5/100,000 cases in 2017 which is a 10.5% increase from 2016 and a 72.7% increase from 2013. This trend is no different in Canada with Alberta being particularly afflicted as one of the provinces with higher rates. Alberta had a 250% increase in the number of infectious syphilis cases in 2018 compared with 2017 (1380 vs 535) (Figure 1). It is no surprise that the laboratories are experiencing a similar rise in the volume of syphilis tests. Polymerase chain reaction (PCR) for detection of primary syphilis is a relatively new test method in the armamentarium of diagnostic tests for syphilis and is not widely available mainly due to the lack of commercially available assays.

Methods The Laboratory for Public Health in Alberta offers an in house syphilis PCR assay. It is a multiplex assay targeting both the tpp47 and polA1 genes and the B2M human DNA control, using TaqMan primers and probes. The assay has been validated for testing lesion swabs.

Results In concert with the rise in infectious syphilis cases, the lab has seen a 68.6% increase in syphilis test volume in 2018 over that of 2017. The positivity rate increased by 23.8% in 2017 and 264.8% in 2018. Direct testing diagnosed 33% (456/1380) of infectious syphilis cases in 2018. The majority of test requests originate from the two STI clinics, serving the inner city populations of the two major cities in the province.

Conclusion With the technical difficulty and quality control issues of the treponemal Direct Fluorescent Antibody test (DFA) and darkfield microscopy, molecular assays can play an important role in identifying early syphilis cases, when serology has the lowest sensitivity, thereby assisting public health in their efforts to decrease transmission.

Disclosure No significant relationships.

  • syphilis

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