Hepatitis C virus genotype 4 cluster with suspected sexual transmission in Chicago, IL

In July 2024, the Chicago Department of Public Health (CDPH) was notified of an increasing number of genotype 4 hepatitis C virus (HCV) infections reported by Illinois Department of Public Health. CDPH initiated a cluster detection investigation. HCV genotype (GT) 4 is most commonly seen in countries in Africa and the Middle East, with limited cases in the United States. HCV GT 4 cases were reported via the Illinois National Electronic Disease Surveillance System (INEDSS). Data were matched across three surveillance systems: enhanced HIV/AIDS reporting system for HIV, Chicago Health Information Management System for syphilis, and INEDSS for Gonorrhea, Chlamydia, and mpox history in Chicago. Cases were interviewed via phone calls or field visits to the patient’s home. A total of 30 HCV GT 4 cases (23 acute and 7 chronic) were reported to the CDPH during March 6, 2023-October 21, 2024. The majority of cases had a history of sexually transmitted infection (STI) within the previous year (77%) and 63% were living with HIV. Cluster cases were male (100%), mostly non-Latino White (40%), with a median age of 37(25–66) years old. Out of 30 cases, 18 (60%) were interviewed, 3 (10%) refused, and 9(30%) were unable to locate. Of those interviewed (n = 18), 83% reported having male sex partners with a median number of 5(2-8.5) partners, and 11% reported current injection drug use (IDU). Overall, 11% of interviewed cases reported IDU, and no common exposure locations were identified. The high number of cases who reported having multiple sexual partners and participation in group sex which led us to conclude that sexual transmission was predominantly the suspected mode of transmission among HCV cluster cases in Chicago, IL.