Concurrency revisited: increasing and compelling epidemiological evidence

Area of Science:

• Epidemiology
• Public Health
• Behavioral Science

Background:

• The role of concurrent sexual partnerships in generalized HIV epidemics in sub-Saharan Africa has been debated, with initial evidence relying on modeling and self-reported data.
• Methodological limitations in early studies prompted a need for more robust epidemiologic evidence to assess the impact of concurrency on HIV transmission.

Discussion:

• Epidemiologic data, particularly from HIV incidence studies, strongly supports concurrency as a key factor in the rapid spread of HIV in generalized epidemics.
• Evidence includes the rapid rise of HIV, transmission patterns in couples, increased risk with multiple partnering, and declines in HIV correlating with reduced concurrency.
• Alternative explanations like serial monogamy or non-sexual transmission do not adequately account for the observed epidemic dynamics.

Key Insights:

• Concurrent partnerships facilitate rapid transmission through sequential acute infections, driving the explosive growth of generalized HIV epidemics.
• A significant portion of HIV transmission occurs within concurrent partnerships, affecting both concordant negative and discordant couples.
• Observed bursts and clustering of infections further implicate concurrency and acute infection in epidemic propagation.

Outlook:

• While other factors like STIs and biological elements may amplify transmission, they likely enhance the role of concurrency rather than replace it.
• Future interventions should integrate messaging about multiple partnering and concurrency to promote safer sexual behaviors and social norms.
• Addressing concurrency is crucial for effective HIV prevention and control strategies in generalized epidemic settings.