Ensuring access to HIV services and harm-reduction interventions earlier could reduce HIV incidence substantially over the course of an actual outbreak, according to a study published in The Lancet.
From 2014 to 2015, Scott County, Indiana, had a significant outbreak of HIV infection among people who inject drugs with a total of 215 incident cases attributed to the outbreak. The first attributed case of HIV infection was diagnosed on November 18, 2014. An investigation by the Indiana State Department of Health began on January 23, 2015, by which time 17 new cases of HIV infection had been recorded. By April 4, 2015, a week after Executive Order 15-05 declared a public health emergency, Scott County established a 30-day temporary syringe-exchange program, but implementation was delayed as a result of conflicts among police officers, people who inject drugs, and those distributing needles. However, Governor Mike Pence did not authorize state officials to establish programs to prevent new HIV infections and treat infected individuals until March 26, 2015. Therefore, questions remain about the timing and scale of the response and whether the scale of the outbreak could have been reduced if the public health response had been implemented before November 2014. This modeling study examined whether earlier implementation of a public health response could have reduced the scale of the outbreak.
The primary objective of this study was to determine whether an earlier response to the outbreak could have influenced the number of people infected. Using weekly case data from the HIV outbreak along with the uptake of HIV testing, treatment, and prevention services from publicly available reports from the US Centers for Disease Control and Prevention and researchers from Indiana, upper and lower bounds for cumulative HIV incidence were computed and a generalization of the susceptible-infectious-removed model was constructed to capture the transmission dynamics of the HIV outbreak. Together, these models were used to assess the potential effect if the same intervention had begun at 2 key time points earlier than the actual date of the initiation of efforts to control the outbreak.
The upper bound for undiagnosed HIV infections in Scott Country peaked at 126 by January 10, 2015, well before the Governor of Indiana declared a public health emergency on March 26, 2015. With the total number of persons infected with HIV estimated at approximately 183 to 184 by August 11, 2015, applying the observed case-finding rate scale up to earlier intervention times suggests that an earlier public health response could have reduced this number substantially. An initiation response on January 1, 2013, could have suppressed the number of people infected with HIV to ≤56, averting at least 127 infections. Further, an initiation response on April 1, 2011, could have reduced the number of incident infections with HIV to 10 or fewer people, averting at least 173 infections.
Overall, the study authors concluded that “[t]his study provides, to our knowledge, the first quantitative evidence that the number of undiagnosed HIV infections had already fallen substantially by the time a public health emergency was declared and syringe-exchange programmes implemented.”
Gonsalves GS, Crawford FW. Dynamics of the HIV outbreak and response in Scott County, IN, USA, 2011-15: a modelling study. Lancet HIV. 208;5:e569-e577.