Modelling the potential impact of homelessness and housing interventions on HIV transmission among people who inject drugs in Pretoria, South Africa

Author: Kennedy Kipkoech, Peter Vickerman, Leigh Johnson, Andrew Scheibe, Hannah Fraser, Jack Stone, Jack Stone

Theme: Epidemiology & Public Health Research Year: 2023

People who inject drugs (PWID) in Pretoria, South Africa, have a high HIV prevalence (58.4% in 2017), and two-thirds of the estimated >8,000 PWID are homeless. Evidence suggests homelessness is an important structural barrier. We estimated the impact of scaling up HIV prevention and treatment interventions among PWID in Pretoria, including the potential importance of housing interventions.

We developed a deterministic model of HIV transmission and homelessness among PWID, parameterised and calibrated using data from Pretoria, including estimates suggesting homelessness increases syringe sharing 1.63-5.01-times. We estimated the percentage of HIV infections prevented over 2022-2030 if homelessness did not increase syringe sharing. The impact of halving levels of homelessness and/or scaling up antiretroviral therapy [ART] (from 17% to 90% of PWID with HIV) and/or harm reduction interventions (from 6% to 50% coverage for opioid agonist therapy [OAT] and 41% to 75% coverage for needle and syringe programmes [NSP]) to UNAIDS targets from 2022, was evaluated as the percentage of HIV infections prevented over 2022-2030 compared to if homelessness and interventions stayed at current levels (status quo SQ).

Removing the effects of homelessness could prevent 75.9% (95% credibility interval [CrI] 64.0-83.2%) of new HIV infections over 2022-2030. If ART or harm reduction are solely scaled-up then 38.3% (95%CrI:30.0-46.3%) and 50.4% (95%CrI:39.4-59.1%) of infections are prevented, respectively, while scaling up both prevents 63.2% (95%CrI:56.1-68.5%) of infections over 2022-2030. If homelessness is also halved, then 74.8% (95%CrI:73.1-76.4%) of infections are prevented. These combined interventions reduce incidence by 95.5% (95%CrI:90.6-97.9%) over 2022 to 2030, while just scaling up ART and harm reduction interventions reduces HIV incidence by 89.0% (95%CrI:82.2-93.4%).

Scaling up ART and harm reduction interventions could yield considerable impact among PWID in South Africa. However, interventions to address structural barriers such as homelessness could also achieve substantial impact.

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