Harm reduction works: extremely low HIV incidence over almost 20 years among people who inject drugs in Australia

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Incidence of new HIV infections among people who inject drugs in Australia is extremely low, results of a retrospective study published in the online edition of AIDS show. Investigators examined incidence among people who inject drugs who had repeat HIV tests between 1995 and 2012. The annual incidence rate remained low throughout the study period at just 0.11 per 100 person-years. The investigators attribute this “remarkable” prevention success to the early introduction of free and legal syringe and needle exchange programmes in Australia.

Globally, an estimated 3 million HIV infections involve people who inject drugs. Research involving 84 countries, conducted in 2007, showed that HIV prevalence among people who inject drugs ranged from 0.01% to 72%.

An understanding of incidence rates among people who inject drugs is important so that prevention campaigns can be planned and evaluated. Research conducted in Australia in the early 1990s found a very low HIV incidence among people who inject drugs (0.17-0.21 per 100 person-years). Investigators examined data obtained between 1995 and 2012 to see if this low incidence rate had been sustained.


person years

In a study “100 person years of follow-up” could mean that information was collected on 100 people for one year, or on 50 people for two years each, or on ten people over ten years. In practice, each person’s duration of follow-up is likely to be different.

retrospective study

A type of longitudinal study in which information is collected on what has previously happened to people - for example, by reviewing their medical notes or by interviewing them about past events. 


Short for people who inject drugs.

The study population involved people who inject drugs who participated in the Australian Needle Syringe Program Survey. To be included in the investigators’ analysis, individuals were required to be HIV negative at baseline and to have had two or more HIV tests at least one year apart during the study period.

A total of 34,000 records were available for analysis. Approximately a quarter (26%; 8873 records) were from the 3528 individuals with repeat test results. After excluding 38 participants who were HIV positive at baseline, the study cohort comprised 3490 individuals who contributed 8763 records.

The median interval between repeat HIV tests was two years. A total of 17 repeat-testers seroconverted for HIV, yielding an incidence rate of 0.11 per 100 person-years (CI: 0.07-0.17).

The majority of incident infections (n = 12; 71%) involved gay men. Incidence was low among gay men but significantly higher among this population than other risk groups (0.83 vs 0.03 per 100 person-years; p < 0.001). No other social or demographic factors were associated with serconversion.

“Results indicate extremely low and sustained HIV incidence over almost two decades”, write the authors. “Consistent with HIV transmission patterns among the broader Australian population, the majority of HIV infections occurred among PWID [people who inject drugs] who identified as MSM [men who have sex with men].”

The authors note that Australia is acknowledged internationally as a leader in harm reduction. They believe that the early introduction of needle and syringe exchanges prevented the emergence of a large-scale HIV epidemic among people who inject drugs. Other factors possibly contributing to the low incidence include migration patterns and the self-limiting nature of HIV outbreaks among people who inject drugs.


Iversen J et al. Extremely low and sustained HIV incidence among people who inject drugs in a setting of harm reduction. AIDS, online edition: DOI: 10.1097/QAD.000000000000068, 2013.