Incidence of syphilis continues to increase among HIV-positive men who have sex with men (MSM) in Ontario. Our objective was to determine the effect of acute syphilis on virologic failure (VF) among virally suppressed HIV-positive MSM taking antiretroviral therapy (ART) and determine if the relationship is confounded by drug use.
The OHTN Cohort Study is a voluntary cohort of people receiving HIV care in Ontario. Syphilis and viral load (VL) data were retrieved via linkage with the provincial laboratory.
Analyses included 2632 MSM from 2008 to 2015, on ART, with ≥1 questionnaire and 2 consecutive VL of <50 copies per milliliter 6 months apart. VF was defined as (1) VL of ≥1000 copies per milliliter or (2) 2 consecutive VLs of ≥200 copies per milliliter ≥1 month apart. We modeled acute syphilis as a time-varying covariate on VF using Poisson regression. Time-varying drug use was assessed for confounding using an iterative process where potential confounders were removed and then reintroduced into the model. Our model allowed for repeat observations using generalized estimating equations.
VF incidence was 3.5 per 100 person-years [95% confidence interval (CI): 3.4 to 4.2]. The rate ratio for VF for acute syphilis was 1.5 (95% CI: 0.9 to 2.4) in the unadjusted model; 1.6 (95% CI: 1.0 to 2.4) in the model adjusted for age, education, region, and income; and 1.2 (95% CI: 0.7 to 1.9) in the final model with additional adjustment for drug use.
Acute syphilis was not associated with VF among virologically suppressed MSM on ART. Consequently, ART may still reduce HIV transmission risk to sexual partners.
aCentre for Urban Health Solutions, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada;
bDalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada;
cPublic Health Laboratories, Public Health Ontario, Toronto, Ontario, Canada;
dDepartment of Medicine, University of Toronto, Toronto, Ontario, Canada;
eInstitute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada;
fDivision of General Internal Medicine, St. Michael's Hospital, Toronto, Ontario, Canada;
gKunin-Lunenfeld Centre for Applied Research and Evaluation, Baycrest Health Sciences, Toronto, Ontario, Canada;
hToronto General Hospital Research Institute, University Health Network, Toronto, Ontario, Canada;
iMount Sinai Hospital, University Health Network, Toronto, Ontario, Canada;
jDepartment of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada;
kDepartment of Psychiatry, University of Toronto, Toronto, Ontario, Canada;
lDivision of Infectious Diseases, St. Michael's Hospital, Toronto, Ontario, Canada; and
mDepartment of Family and Community Medicine, St. Michael's Hospital, Toronto, Ontario, Canada.
Correspondence to: Ann N. Burchell, PhD, Department of Family and Community Medicine, Li Ka Shing Knowledge Institute, St. Michael's Hospital, 30 Bond Street, Toronto, ON M5B 1W8, Canada (e-mail: firstname.lastname@example.org).
Supported by the Canadian Institutes of Health Research operating grant 111146, CIHR/Ontario HIV Treatment Network New Investigator Award to D.H.S.T, an OHTN Chair to J.R. and a Fondation Baxter & Alma Ricard Chair in Inner City Health at St. Michael's Hospital for A.M.B. The OHTN Cohort Study is funded by the AIDS Bureau, Ontario Ministry of Health and Long-Term Care.
Presented at the STI & HIV World Congress; July 9–12, 2017; Rio de Janeiro, Brazil; and the Canadian Association for HIV Research Conference; April 6–9, 2017; Montreal, Canada.
T.O. is currently employed at Roche Diagnostics. The remaining authors have no funding or conflicts of interest to disclose.
Members are listed in Appendix 1.
The opinions, results, and conclusions are those of the authors only. No endorsement by the Ontario HIV Treatment Network or Public Health Ontario is intended or should be inferred.
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Received September 13, 2018
Accepted December 27, 2018