partial secular trend effect on the intervention group's observed drug-use risk behavior change.

There are a number of other possible uncontrolled factors that could account for the observed reduction in the injection drug-use risk behaviors and HIV seroconversion. Although participants were not "selected" for services on the basis of their measured level of risk, it is possible that they agreed to become a participant when their needle risk was at an abnormally high level. Due to maturation or instability in their levels of use, we would expect that on subsequent assessment, these clients would reveal a lower level of risk behavior (i.e., they would regress toward the population mean). Without a control group, it is not possible to assess the extent to which trait instability or maturation is at work.

Saturation of the at-risk pool of injectors (which happens when most of the susceptible injectors have already been infected) is yet another possible alternative explanation for the result depicted in Figure 6.1. Although the Chicago researchers contend that saturation could not account for the reported decline in seroincidence, because HIV seroprevalence remained constant in their cohort at 32 percent throughout their prospective study, it is still possible that saturation did impact on their findings. That is, saturation among those who remained susceptible (susceptibility being defined on the basis of risk of exposure through drug-use risk behavior) may have occurred, given that a substantial proportion of the cohort removed their risk of exposure (i.e., their drug-use risk behavior) and were no longer in the pool of susceptibles (assuming no risk of exposure through sexual-risk behavior).

Nonetheless, the data tend to suggest that there was a decrease in risky drug-use behavior over time, with an attendant decrease in new HIV infection in the cohort as originally assembled (irrespective of other risk behaviors).3 It also highlights that bleach distribution occurs in the context of street outreach, making it difficult to disentangle bleach effect per se from the outreach worker effect. Moreover, the corresponding decline in self-report drug-use risk behavior and HIV incidence does also provide supporting evidence for the construct validity of self-report data.

The null results of epidemiologic studies reviewed earlier in conjunction with the program evaluation results reviewed above reveal the potential critical role of outreach activities in achieving meaningful behavioral change. In fact, these investigators (Wiebel et al., 1994) reported that injection drug users in the study group most frequently reduced risk not by always using bleach to clean injection equipment, but, rather, by eliminating the sharing of syringes and other injection equipment altogether. These changes in injection practices occurred over a time when there was no syringe exchange in Chicago, nor were there local laws permitting the possession of



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