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Swifter public health response could have prevented Indiana HIV outbreak

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September 25, 2018

In March 2015, then-Indiana Gov. Mike Pence declared a public health emergency in response to a large HIV outbreak in Scott County among people who inject drugs, or PWID, launching a temporary needle exchange program that research has shown led to a reduction in risky behaviors among PWID. But newly published findings show that Pence’s declaration came 2 months after HIV infections actually peaked in the outbreak, and that the number of infections could have been substantially reduced if the public health response came sooner.

“Although Governor Pence eventually authorized state officials to establish programs to prevent new HIV infections and treat infected individuals on March 26, 2015, questions remain about the timing and scale of the response,” Yale School of Public Health researchers Gregg S. Gonsalves, PhD, associate professor of epidemiology, and Forest W. Crawford, PhD, associate professor of biostatistics and ecology and evolutionary biology, wrote in The Lancet HIV. “In this study, we used published time series of HIV diagnoses in Scott County and associated estimated HIV infection dates based on recency assay results to reconstruct the dynamics of the Scott County HIV outbreak and the public health response from 2011 to 2015.”

Using publicly available reports from the CDC and Indiana researchers, Gonsalves and Crawford collected weekly case data from the outbreak, as well as data regarding the uptake of HIV testing, treatment and prevention services to determine if an earlier response to the outbreak would have affected the number of infections. They extracted data from a CDC report to formulate upper and lower bounds for the cumulative HIV incidence and estimated the recency of each transmission event.

They used modeling to “capture the transmission dynamics” of the outbreak and estimated the number of individuals with an undiagnosed HIV infection, the case-finding rate per undiagnosed HIV infection and model-based bounds for the HIV transmission rate throughout the epidemic. These models were used to investigate the potential effect of initiating the same interventions at two earlier key time points in 2011 and 2013.

According to Gonsalves and Crawford, undiagnosed HIV infections peaked in Scott County at 126 cases around Jan. 20, 2015 — 2 months before the public health emergency declaration on March 26, 2015, by then-Governor Mike Pence.

The researchers estimated that the outbreak included between 183 and 184 infections by Aug. 11, 2015. They calculated that a public health intervention initiated in April 2011 could have reduced the number of HIV infections in the outbreak to 10 or fewer.

An intervention began in in January 2013 could have reduced the cumulative HIV incidence to between zero and 56 cases by Aug. 11, 2015, they said.

Gonsalves and Crawford noted that the initial infections causing the outbreak were not detected for several years. In 2014, when the outbreak erupted, months went by without recognition from state or local officials and it took a full year for a public health response to begin, they said.

According to the study, in 2008, local experts recommended that syringe-exchange programs be established to prevent infectious disease outbreaks. However, even after Indiana’s 2010 to 2011 hepatitis C virus outbreak among PWID, “these recommendations remained unheeded.” Moreover, the state’s only HIV testing provider closed in 2013 because of state funding cuts. This, according to Gonsalves and Crawford, “could have delayed the diagnosis of the initial case of HIV infection in Scott County.”

“The conservative nature of our approach, [including] using actual data on diagnoses, nonparametric bounds for cumulative incidence, and not assuming an effect of syringe-exchange programs on the transmission rate, suggests that had the interventions deployed in Scott County in 2014–15 been available earlier, the outbreak might have been substantially blunted,” the researchers wrote. “Future HIV outbreaks could be minimized if HIV testing and treatment are available in places vulnerable to the transmission of blood-borne infections among PWID. Syringe-exchange programs and use of opioid-agonist therapy are crucial HIV prevention tools that could offer the chance to prevent new outbreaks among PWID.” – by Marley Ghizzone

Disclosures: The authors report no relevant financial disclosures.

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