BACKGROUND: Between 2011 and 2015, there were 3,267 cases of chronic hepatitis C (HCV) infection reported in St. Louis County, but no cases of acute HCV infection. HCV case reports generally lack the clinical data needed to distinguish between acute and chronic infection. The St. Louis County Department of Public Health (DPH) has historically lacked the capacity to investigate HCV cases. Accordingly, DPH also lacks data about cases’ histories with respect to injection drug use (IDU) – the leading risk factor for acute HCV infection. However, DPH has data about deaths due to heroin overdose in St. Louis County, which can be used as a proxy variable for IDU. This study sought to determine what proportion of chronic HCV cases might represent new infections, and how this proportion has changed over time.
METHODS: This analysis included all non-institutionalized St. Louis County residents with HCV infections reported between 2011 and 2015. According to death certificate data, males, people aged 25 to 44 years, and people living in the South and Inner North regions of St. Louis County had the highest rates of death from heroin overdose between 2010 and 2014. Using data from Missouri’s reportable diseases database, the proportion of HCV infections represented by each of these high-risk groups was calculated.
RESULTS: Chronic HCV cases increased by 57.4% between 2011 (n=578) and 2015 (n=910). Males accounted for 62.8% (n=363) of cases in 2011 and 62.0% (n=564) of cases in 2015. People aged 25 to 44 years accounted for 18.3% (n=106) of cases in 2011 and 32.3% (n=294) of cases in 2015. People living in Inner North or South St. Louis County accounted for 36.5% (n=211) of cases in 2011 and 52.0% (n=473) of cases in 2015. People with any two of these risk factors accounted for 29.2% of cases in 2011 and 38.6% of cases in 2015. People with all three risk factors accounted for 2.8% of cases in 2011 and 10.8% of cases in 2015.
CONCLUSIONS: The groups at greatest risk of dying from a heroin overdose in St. Louis County represented a greater proportion of HCV infections in 2015 than in 2011. This suggests a possible increase in HCV transmission among a population at high risk for acute HCV infection. This analysis is limited by the use of a proxy variable for IDU, but these results could be useful in targeting scarce resources for case investigation and prevention efforts.