Study asks: What if a “concentrated” HIV epidemic is bigger than 1 percent?

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In a “generalized HIV epidemic,” what if all transmission during sex work stopped?

Call it a different kind of 1 percent — the kind that doesn’t connote privilege. In the definition that sets the course of HIV programming, an epidemic is considered “concentrated” among specific populations, (i.e. JAIDScoversex workers, people who inject drugs, and men who have sex with men) if HIV prevalence among a population as a whole is less than one percent. In that case, the need to focus prevention efforts on those “key” populations is acknowledged. But when an epidemic has spread among more than 1 percent of the population as a whole, it is considered “generalized,” and if the interventions targeting the general population also reach populations marginalized by laws, policies, and stigma, they are welcome to them. But what if the definitions of concentrated and generalized confuse, rather than inform HIV interventions? What if, for example, failures to reach sex workers and their clients is responsible for a higher general prevalence than previously assumed?

Researchers led by Marie-Claude Boily of the Department of Infectious Disease Epidemiology at Imperial College in London, did the math to answer that question using sexual behavior and health data from across west and central Africa. They created 1000 hypothetical epidemics from the data and followed them. They found that HIV prevalence across a population driven by sex work in west and central Africa can be as high as 12 percent. In other words, an epidemic can spread beyond 1 percent of a general population,  and still be driven by failures to reach one specific population.

Instead of being defined by a number, the authors concluded, “concentrated epidemics should be defined as [those] where vulnerabilities and risk behaviors in a small fraction of a population can lead to a disproportionate amount of HIV transmission, and sustain onward transmission.”

More accurately defining the nature of their epidemics, the authors note, will help governments to target their responses for maximum effectiveness.

The report on the study, What Really is a Concentrated HIV Epidemic and What Does it Mean for West and Central Africa?, is part of a Journal of Acquired Immune Deficiency Syndromes supplement on HIV Risks and Vulnerabilities Among Key Populations in West and Central Africa.

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