Testing and Treatment Interventions in Community Settings Key to Controlling a Recent Human Immunodeficiency Virus Outbreak Among People Who Inject Drugs in Glasgow: A Modeling Study

Background:
An HIV outbreak was identified among people who inject drugs (PWID) in Glasgow in 2015, with over 150 diagnoses by the end of 2019. The outbreak response involved scaling-up HIV testing and improving HIV treatment initiation and retention.

Methods:
We parameterised and calibrated a dynamic, deterministic model of HIV transmission among PWID in Glasgow to epidemiological data. We use this model to evaluate HIV testing and treatment interventions. We present results in terms of relative changes in HIV prevalence, incidence and cases averted.

Results:
If the improvements in both testing and treatment had not occurred, we predict that HIV prevalence would have reached 17.8% (95%CrI 14.1-22.6) by the beginning of 2020, compared to 5.9% (95%CrI 4.7-7.4) with the improvements. If the improvements had been made on detection of the outbreak in 2015, we predict that peak incidence would have been 26.2% (95%CrI 8.8-49.3) lower and 62.7% (95%CrI 43.6-76.6) of the outbreak cases could have been averted. The outbreak could have been avoided if the improvements had
already been in place.

Conclusions:
Our modelling suggests that the HIV testing and treatment interventions successfully brought the HIV outbreak in Glasgow under control by the beginning of 2020.