BACKGROUND: The burden of chronic hepatitis C virus (HCV) infection was previously unknown in Salt Lake County (SLCo), Utah, due to limited surveillance capacity. To address this gap, we reclassified cases according to the 2016 CSTE/CDC chronic hepatitis C case definition and explored the data to build an epidemiologic profile of chronic HCV infection in Salt Lake County.
METHODS: Chronic HCV cases reported during 1990-2015 were reviewed and re-assigned a case status according to the 2016 case definition. Descriptive and spatial analyses were performed on confirmed and probable cases and rates were calculated per 100,000. To assess co-morbidities, chronic HCV cases were matched to hepatitis C and drug poisoning deaths (2007-2014) and to liver transplant recipients (1992-2014). To assess co-infections, chronic HCV cases were matched to surveillance data including chlamydia, gonorrhea, syphilis, invasive group A streptococcal disease (2009-2015), HIV/AIDS and hepatitis B (1988-2015). Matched results were manually reviewed to determine true matches.
RESULTS: Reclassification identified an additional 11,760 cases of chronic HCV infection, totaling 19,897 cases, reported during 1990-2015. The 2015 age-adjusted incidence rate was 116.1 (109.5-122.7) and the 2010-2014 age-adjusted mortality rate was 0.813 (0.554-1.072). Incidence was two times higher among males than females, particularly among males aged 55 years and older. Co-morbidities included hepatitis B (2%), chlamydia (1%), drug poisoning deaths (1%) and HIV/AIDS (1%); less than 0.5% of chronic HCV cases received a liver transplant post-HCV diagnosis. Eighty percent of hepatitis C deaths matched to chronic HCV cases. At least 7% of cases cleared infection. Spatial analysis revealed one neighborhood with increasingly high case counts over time.
CONCLUSIONS: Use of the 2016 case definition resulted in a higher rate of chronic HCV infection; previous case definitions relied heavily on interpretation of antibody results, leading to many cases with an unknown case status. Our 2015 incidence rate was higher than the 2014 incidence rate in most CDC Enhanced Viral Hepatitis Surveillance Sites. Approximately one-fifth of hepatitis C-related deaths may have been due to undiagnosed chronic HCV infection. The unexpectedly low percentages of co-morbidities may also be due to a large proportion of undiagnosed HCV-infected individuals. Robust surveillance and data quality improvements are needed to better characterize affected populations.