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Spatial-Temporal Epidemiology of the Syphilis Epidemic in Relation to Neighborhood-Level Structural Factors in British Columbia, 2005–2016

Salway, Travis PhD*,†; Gesink, Dionne PhD; Lukac, Christine MPH; Roth, David PhD; Ryan, Venessa MPH; Mak, Sunny MSc; Wang, Susan MSc; Newhouse, Emily MD§; Hayden, Althea MD§; Bharmal, Aamir MD; Hoyano, Dee MD; Morshed, Muhammad PhD*,**; Grennan, Troy MD*,†; Gilbert, Mark MD*,†; Wong, Jason MD*,†

doi: 10.1097/OLQ.0000000000001034
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Background Spatial clusters of syphilis have been observed within several jurisdictions globally; however, the degree to which they are predicted by the spatial distributions of gay, bisexual, and other men who have sex with men (GBM) and testing remains unknown. We sought to describe the spatial-temporal epidemiology of infectious syphilis and identify associations between neighborhood-level factors and rates of syphilis, in British Columbia, Canada.

Methods We used ArcGIS to map infectious syphilis cases among men (2005 to 2016), SaTScan to detect areas with significantly elevated rates of syphilis, and spatial regression to identify associations between neighborhood-level factors and rates of syphilis.

Results Five clusters were identified: a core in downtown Vancouver (incidence rate ratio [IRR], 18.0; 2007–2016), 2 clusters adjacent to the core (IRR, 3.3; 2012–2016; and IRR, 2.2; 2013–2016), 1 cluster east of Vancouver (IRR, 2.1; 2013–2016), and 1 cluster in Victoria (IRR, 4.3; 2015–2016). Epidemic curves were synchronized across cluster and noncluster regions. Neighborhood-level GBM population estimates and testing rates were both associated with syphilis rates; however, the spatial distribution of syphilis was not fully explained by either of these factors.

Conclusions We identified two novel ecologic correlates of the spatial distribution of infectious syphilis—density of GBM and rates of syphilis testing—and found that these factors partially, though not entirely, explained the spatial distribution of clusters. Residual spatial autocorrelation suggests that greater syphilis testing coverage may be needed and low-barrier GBM-affirming testing should be expanded to regions outside the core.

Infectious syphilis was spatially concentrated in British Columbia, Canada. Rates of syphilis were partially correlated with area-level density of gay and bisexual men and rates of testing.

From the *School of Population and Public Health, Department of Pathology and Laboratory Medicine, and Department of Medicine, University of British Columbia

Clinical Prevention Services and Public Health Analytics, British Columbia Centre for Disease Control, Vancouver, BC

Dalla Lana School of Public Health, University of Toronto, Toronto, ON

§Vancouver Coastal Health, Vancouver

Fraser Health, Surrey

Island Health, Victoria, BC

**British Columbia Centre for Disease Control Public Health Laboratory, Vancouver, Canada

Conflicts of interest and sources of funding: None declared.

Correspondence: Travis Salway, PhD, BC Centre for Disease Control, 655 West 12th Ave, Vancouver, BC, Canada V5Z 4R4. E-mail: travis.salway@bccdc.ca.

Received for publication March 21, 2019, and accepted June 3, 2019.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text, and links to the digital files are provided in the HTML text of this article on the journal’s Web site (http://www.stdjournal.com).

Online date: June 27, 2019

© Copyright 2019 American Sexually Transmitted Diseases Association