The cumulative impact of harm reduction on the Swiss HIV epidemic: cohort study, mathematical model and phylogenetic analysis. Open Forum Infectious Diseases
Marzel et al. aimed to perform a quantitative evaluation of the cumulative impact of implemented harm reduction measures in Switzerland on the HIV incidence and prevalence among injecting drug users (IDUs). For that, they constructed a compartmental, deterministic transmission model represented as a nonlinear system of 32 ordinary differential equation. This model reconstructed the national epidemic into the IDUs population from the first HIV case in 1980 until 2015. The authors used phylogenetic cluster analysis of HIV-1 pol sequences to quantify the epidemic spillover from IDUs to the general population.
Overall, harm reduction prevented 15’903 (range, 15’359–16’448) HIV infections among IDUs until the end of 2015, 5’446 acquired immune deficiency syndrome (AIDS) deaths (range, 5’142–5’752), and a peak HIV prevalence of 50.7%. Introduction of harm reduction 2 years earlier could have halved the epidemic, preventing 3’161 (range, 822–5’499) HIV infections and 1’468 (range, 609–2’326) AIDS deaths. Suddenly discontinuing all harm reduction in 2005 would have resulted in outbreak re-emergence with 1’351 (range, 779–1’925) additional HIV cases. Without harm reduction, the estimated additional number of heterosexuals infected by HIV-positive IDUs is estimated to have been 2’540 (range, 2’453–2’627), which is equivalent to the total national reported incidence among heterosexuals in the period of 2007 to 2015.
In conclusion, the proposed model estimated that a very high prevalence of HIV (~50%) among IDUs would have occurred in the absence of harm reduction. The study-results highlight, based on the Swiss experience, the pivotal role of harm reduction for successful curbing of HIV transmission among IDUs and prevention of grave repercussions for the general population.