COMMENTARIES Comments on Stimson ’ s a Has the United Kingdom averted an epidemic of HIV - 1 infection among drug injectors ?

In his editorial, Stimson argues that the prevention efforts undertaken in the United Kingdom were effective in averting an epidemic of HIV infection among injecting drug users in that country. Having made similar arguments for a prevented epidemicso among injecting drug users in ® ve speci® c cities, I tend to ® nd Stimson’ s arguments convincing. Of course, demonstrating causation is particularly dif® cult in what are essentially epidemiological community case histories. Cordray’ s analysis of quasi-experimental design issues can be very useful in establishing a logic of causation in these types of data. The apparent success of the HIV prevention programs in the United Kingdom and elsewhere raises the question of a what next?o for both public health practice and research with injecting drug users in the areas which have not (yet) experienced epidemics of HIV. Recent preliminary data from Canada offer a cautionary note. Vancouver has experienced an increase in HIV incidence among IDUs and Toronto has seen an increase in HIV prevalence among IDUs who engage in male-with-male sex. These increases in HIV infection among IDUs have occurred despite prevention efforts in those cities. Clearly, we are not at a stage where we should consider HIV prevention among IDUs to be a completed task, and should not reduce current prevention efforts. We do not yet really understand how prevention programs might avert an HIV epidemic. We do know that successful HIV prevention programs do not eliminate risk behaviorÐ a sharingo of injection equipment or having unprotected sex among IDUs. The London data collected by Stimson and colleagues as well as the Glasgow data collected by Goldberg and colleagues show that moderate numbers of IDUs in those cities report injecting with equipment used by others in the previous 6 months. In Lund, Sweden, where HIV prevalence among IDUs is approximately 2% and quite stable, 58% of IDUs report some injecting with equipment used by others in the previous 6 months. It may be time to replace a any sharingo as our primary variable in studies of IDUs in places like the United Kingdom. In low HIV seroprevalence areas, injection risk behavior that is con® ned within small groups of IDUs is very unlikely to lead to HIV transmission. This a risk behaviouro is occurring almost exclusively among people who are HIV negative, so that it is not a meaningful indicator of possible HIV transmission. a Sharingo of injection equipment with large numbers of other people, with strangers or casual acquaintances, within prisons, or using a dealer’s workso may all be much more likely to lead to HIV transmission within low seroprevalence areas. Understanding stable low HIV seroprevalence among populations of IDUs that continue some a sharingo may require that we