Mathematical modelling of the influence of serosorting on the population-level HIV transmission impact of pre-exposure prophylaxis

Linwei Wang; Nasheed Moqueet; Anna Simkin; Jesse Knight; Huiting Ma; Nathan J Lachowsky; Heather L Armstrong; Darrell H S Tan; Ann N Burchell; Trevor A Hart; David M Moore; Barry D Adam; Derek R Macfadden; Stefan Baral; Sharmistha Mishra

doi:10.1097/QAD.0000000000002826

Mathematical modelling of the influence of serosorting on the population-level HIV transmission impact of pre-exposure prophylaxis

AIDS. 2021 Jun 1;35(7):1113-1125. doi: 10.1097/QAD.0000000000002826.

Authors

Linwei Wang¹, Nasheed Moqueet¹, Anna Simkin¹, Jesse Knight^{1

2}, Huiting Ma¹, Nathan J Lachowsky³, Heather L Armstrong^{4

5}, Darrell H S Tan^{1

6

7}, Ann N Burchell^{1

8

9}, Trevor A Hart^{9

10}, David M Moore^{4

11}, Barry D Adam¹², Derek R Macfadden⁶, Stefan Baral¹³, Sharmistha Mishra^{1

2

6

7}

Affiliations

¹ MAP-Centre for Urban Health Solutions, St. Michael's Hospital, Unity Health Toronto.
² Institute of Medical Sciences, University of Toronto, Toronto, Ontario.
³ School of Public Health and Social Policy, University of Victoria, Victoria.
⁴ British Columbia Centre for Excellence in HIV/AIDS, Vancouver, British Columbia, Canada.
⁵ School of Psychology, University of Southampton, Southampton, UK.
⁶ Department of Medicine.
⁷ Institute of Health Policy, Management, and Evaluation.
⁸ Department of Family and Community Medicine.
⁹ Dalla Lana School of Public Health, University of Toronto.
¹⁰ Department of Psychology, Ryerson University, Toronto, Ontario.
¹¹ Department of Medicine, Division of Infectious Disease, University of British Columbia, Vancouver, British Columbia.
¹² Department of Sociology, Anthropology, and Criminology, University of Windsor, Windsor, Ontario, Canada.
¹³ Department of Epidemiology, Johns Hopkins University, Baltimore, Maryland, USA.

Abstract

Objectives: HIV pre-exposure prophylaxis (PrEP) may change serosorting patterns. We examined the influence of serosorting on the population-level HIV transmission impact of PrEP, and how impact could change if PrEP users stopped serosorting.

Design: We developed a compartmental HIV transmission model parameterized with bio-behavioural and HIV surveillance data among MSM in Canada.

Methods: We separately fit the model with serosorting and without serosorting [counterfactual; sero-proportionate mixing (random partner-selection proportional to availability by HIV status)], and reproduced stable HIV epidemics with HIV-prevalence 10.3-24.8%, undiagnosed fraction 4.9-15.8% and treatment coverage 82.5-88.4%. We simulated PrEP-intervention reaching stable pre-specified coverage by year-one and compared absolute difference in relative HIV-incidence reduction 10 years post-intervention (PrEP-impact) between models with serosorting vs. sero-proportionate mixing; and counterfactual scenarios when PrEP users immediately stopped vs. continued serosorting. We examined sensitivity of results to PrEP-effectiveness (44-99%; reflecting varying dosing or adherence levels) and coverage (10-50%).

Results: Models with serosorting predicted a larger PrEP-impact than models with sero-proportionate mixing under all PrEP-effectiveness and coverage assumptions [median (interquartile range): 8.1% (5.5-11.6%)]. PrEP users' stopping serosorting reduced PrEP-impact compared with when PrEP users continued serosorting: reductions in PrEP-impact were minimal [2.1% (1.4-3.4%)] under high PrEP-effectiveness (86-99%); however, could be considerable [10.9% (8.2-14.1%)] under low PrEP effectiveness (44%) and high coverage (30-50%).

Conclusion: Models assuming sero-proportionate mixing may underestimate population-level HIV-incidence reductions due to PrEP. PrEP-mediated changes in serosorting could lead to programmatically important reductions in PrEP-impact under low PrEP-effectiveness. Our findings suggest the need to monitor sexual mixing patterns to inform PrEP implementation and evaluation.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Anti-HIV Agents* / therapeutic use
Canada
HIV Infections* / drug therapy
HIV Infections* / prevention & control
HIV Serosorting
Homosexuality, Male
Humans
Male
Pre-Exposure Prophylaxis*
Sexual and Gender Minorities*

Substances

Anti-HIV Agents

Grants and funding

FN-13455/CIHR/Canada