S09.4 Prevalence of molecular markers for azithromycin resistance found in Treponema pallidum in British Columbia, Canada

Abstract

<h3>Introduction</h3> In 2000, BC Centre for Disease Control (BCCDC) executed a mass treatment campaign with azithromycin in an attempt to curb a syphilis outbreak. As a result of mass treatment, syphilis case numbers decreased temporarily, but within two years the outbreak began to ramp up again. An antibiotic resistance study was performed on selected samples from the past 20 years in British Columbia to understand the local trends of azithromycin-resistant syphilis in BC. <h3>Materials/Methods</h3> BCCDC Public Health Laboratory selected positive (n=273) samples from 2000 to 2019 for azithromycin resistance testing. A two reaction RFLP (Restriction Fragment Length Polymorphism) panel was designed to detect two possible mutations in the 23S rRNA gene of Treponema pallidum, which confer azithromycin resistance. <h3>Results</h3> Among samples tested, over 75% contained one of the two mutations leading to macrolide resistance. The majority of the samples had the A2058G mutation. Only four of the screened samples tested positive for the A2059G mutation. None of the samples that were tested contained both resistance-conferring mutations in the 23S rRNA gene. To note only about 8.5% (5/59) of specimens collected in the first 10 years were drug resistant. Although case of azithromycin-resistant T. pallidum were detected in 2000, almost no additional resistant cases were detected among selected specimens for the next 10 years, except four cases in year 2004. In contrast, the drug resistance prevalence drastically increased to 93.9% (201/214) over the next 10 years (2010–2019). <h3>Conclusions</h3> While azithromycin is not first or second choice in recommended syphilis treatment regimen in British Columbia, it is a drug of choice for many countries in other parts of the world; increasing azithromycin drug resistance, therefore, is a real global concern. In this presentation we will discuss the positivity rate for azithromycin resistance-conferring point mutations observed in our positive T. pallidum PCR samples.