Collection of negative hepatitis C virus (HCV) antibody (Ab) results can aid surveillance by increasing identification of acute HCV infections. Negative to positive seroconversion of HCV-Ab is indicative of a recent exposure to HCV. The 2015 CSTE acute HCV case definition includes HCV Ab seroconversions that occur within one year, increased from six month seroconversion time period used in the 2012 definition. This study attempts to assess HCV seroconversion and seroincidence rates in Philadelphia.
METHODS:
The Philadelphia Department of Public Health (PDPH) collected 2012 - 2015 negative HCV Ab results from commercial and hospital laboratories. Negative HCV Ab test results were matched to 2013-2015 HCV Ab positive results housed in the PDPH hepatitis registry, allowing 12 months for the earliest seroconversions to occur. Seroincidence was calculated as the percentage of seroconversions occurring among individuals with an HCV Ab negative result followed by at least one additional HCV Ab test. Seroconversion cases and their providers were contacted to assess clinical and risk factor information about their disease.
RESULTS:
During 2012 - 2015, 152,632 people had at least one negative HCV Ab result, 9% (n=13,422) of whom had an additional HCV test result after the negative. There were 426 seroconversions in the study period, resulting in a 3% (426/13,422) seroincidence, and a 2% (126/6,213) seroincidence when the analysis was limited to individuals who were re-tested within 12 months of a negative result. Individuals 18-30 years of age were more likely to be tested twice, but no more likely to seroconvert as individuals ≥30 years. While 65% (n=3922) of individuals tested ≥2X in a 12 month period were female, males were more likely to seroconvert (1% vs 3%, p-value<0.001). Of investigated cases, 71% had a history of injection drug use, HIV infection, incarceration, hemodialysis, MSM, or homelessness and 14% had documented symptoms or jaundice.
CONCLUSIONS:
This study demonstrates the utility of obtaining negative HCV Ab test results and matching to HCV Ab positive test results to identify recent HCV seroconversions. Since repeat screening for HCV is frequently performed on high-risk individuals such as those receiving methadone or dialysis, or those repetitively incarcerated, seroconversion data can allow Health Departments to more accurately assess rates of acute infection in these populations. Further, without knowledge about case symptoms or jaundice, analyzing HCV laboratory data for seroconversion is a critical mechanism for identifying acute disease.