title: Ignoring 'downstream infection' in the evaluation of harm reduction interventions for injection drug users.
abstract: Harm reduction interventions to reduce blood-borne disease incidence among injection drug users (IDUs). A common strategy to estimate the long-term impact of such interventions is to examine short-term incidence changes within a specific group of individuals exposed to the intervention. Such evaluations may overstate or understate long-term program effectiveness, depending upon the relationship between short-term and long-term incidence and prevalence. This short paper uses steady-state comparisons and a standard random-mixing model to scrutinize this evaluation approach. It shows that evaluations based upon short-term incidence changes can be significantly biased. The size and direction of the resulting bias depends upon a simple rule. For modest interventions, such analyses yield over-optimistic estimates of program effectiveness when steady-state disease prevalence exceeds 50% absent intervention. When steady-state prevalence is below 50%, such analyses display the opposite bias.
authors.affiliation: University of Michigan School of Public Health, Ann Arbor 48109-2029, USA. haroldp@sph.umich.edu
authors.forename: H A
authors.initials: HA
authors.lastname: Pollack
mesh_terms: D017848:Blood-Borne Pathogens; D003140:Communicable Disease Control / Q000706:statistics & numerical data*; D006801:Humans; D018671:Needle-Exchange Programs / Q000706:statistics & numerical data*; D015397:Program Evaluation / Q000706:statistics & numerical data; D015819:Substance Abuse, Intravenous / Q000150:complications*