A large healthcare-associated outbreak of hepatitis C virus genotype 1a in a clinic in Korea

Among the 1721 patients tested, 96 were IgG-positive and 70 were viral RNA-positive. Among the 61 patients whose viral loads were greater than the detection limit, 41 (67.2%) were classified as genotype 1a, 1 (1.6%) as genotype 1b, 18 (29.5%) as genotype 1, and one (1.6%) as genotype 2. After sequencing, 12 genotype 1 cases were further classified as genotype 1a (11) or 1b (1). The sequences of the core-E2 and NS5B regions of 45 patients formed a monophyletic cluster distinct from genotype 1a. The hepatitis C virus sequences from patients and environmental specimens were well-matched in the partial E1 gene region. We detected genotype 1a RNA in environmental specimens, indicating a healthcare-associated outbreak caused by reuse of syringes and contaminated multi-dose vials. Our molecular epidemiological investigation of hepatitis C genotype 1a, rare in Korea, will aid investigations of infection sources during future pathogen outbreaks.