Higher risk profiles account for the high rates of HIV infection among injection drug users who participate in needle exchange programs, not participation in the program itself, according to researchers in Canada.

Very subtle differences in early studies that evaluated the effects of estrogen replacement therapy in menopausal women provided misleading findings. The same types of factors make the Vancouver needle exchange program appear to be less effective than it really is, co-investigator Dr. Evan Wood told Reuters Health. All of the higher risk factors were much more common among drug users who frequently attended the needle exchange program.

In a study of injection drug users, Wood, from the British Columbia Centre for Excellence in HIV/AIDS, Vancouver, and colleagues, evaluated possible explanations for the association between high HIV infection rates and frequent needle exchange program attendance.

Compared with those who did not attend the needle exchange program each day, daily needle exchange attendees were more likely to be female, Aboriginal or American Indian, in unstable housing, Downtown Eastside residents, involved in the sex trade, daily heroin users, daily cocaine users, and “shooting gallery” users, the researchers found.

Virtually all of these risk factors are associated with an increased HIV incidence, according to the study findings, reported in The American Journal of Medicine.

In fact, the researchers note, after accounting for all other variables that are significantly associated with HIV transmission, the increased risk for HIV infection among daily needle exchange program attendees versus non-daily needle exchange attendees was no longer statistically significant.

“In sum, the present study demonstrates that the reason for the previously reported association between frequent needle exchange program use and HIV infection in Vancouver is that higher-risk injection drug users tend to use the needle exchange more frequently in this setting,” the researchers write.

These findings “should be useful for policy-makers internationally who have had persistent concerns about earlier reports,” the authors point out.

“Preventing HIV infection is extremely challenging,” Wood said. “While programs like needle exchange get held to an extraordinary standard of evidence, in reality, the bulk of public resources go to programs that go totally unevaluated. For instance, the rate of incarceration of non-violent drug offenders is creating a range of health and social problems, and yet few if any are discussing if this strategy is effective.”

While needle exchange programs have been shown to reduce HIV rates, Wood added, “another important goal they achieve is making contact with this often hidden population and providing a venue where drug users can be recruited into addiction treatment and other forms of care.”

SOURCE: The American Journal of Medicine, February 2007.