The Contribution of Unstable Housing to HIV and Hepatitis C Virus Transmission Among People Who Inject Drugs Globally, Regionally, and at Country Level: A Modelling Study

Background: People who inject drugs (PWID) experience high levels of unstable housing which is associated with increased HIV and hepatitis C virus (HCV) acquisition risk. We estimated the contribution of unstable housing to HIV and HCV transmission among PWID globally, regionally, and at country level.

Methods: We developed simple dynamic deterministic models of unstable housing and HIV/HCV transmission to simulate country-level HIV/HCV epidemics among PWID. Each country’s model was calibrated using country-specific data from systematic reviews on duration of injecting, mortality, and prevalences of unstable housing, HIV and HCV among PWID. Based on our recent systematic review and meta-analysis, unstably housed PWID were assumed to have a 39% (95%CI: 6-84) and 64% (95%CI: 43-89%) higher risk of HIV and HCV transmission, respectively, than stably housed PWID. We estimated the transmisison population attributable fraction (tPAF) of HIV and HCV transmission associated with unstable housing, defined as the percentage of infections prevented over 2020-2029 by removing the additional transmission risk due to unstable housing.

Results: The HIV and HCV models included 56 and 55 countries, respectively (> two-thirds of the global PWID population). Globally, unstable housing contributes 7·9% (95% credibility interval [CrI] 2·3–15·7) of new HIV infections and 11·2% (7·7–15·5) of new HCV infections among PWID over 2020-2029. TPAFs were greater across high-income countries (HIV 17·2% [95%CrI 5·1–30·0]; HCV 19·4% [95%CrI 13·8–26·0]) than low/middle-income countries (HIV 6·6% [95%CrI 1·8–13·1]; HCV 8·3% [95%CrI 5·5–11·7]). The greatest tPAFs were estimated in Afghanistan, Czech Republic, India, USA, England, and Wales where unstable housing contributes more than 20% of new HIV and HCV infections.

Conclusion: Unstable housing is an important modifiable risk factor for HIV and HCV transmission among PWID in many countries. The study emphasises the importance of implementing initiatives to mitigate these risks and reduce housing instability.