Study on Hepatitis C virus (HCV) subtypes in Sweden before and after the universal screening of blood donors

Abstract: Since the discovery in 1989 of hepatitis C virus (HCV) as the infectious agent responsible for the vast majority of post-transfusion non-A non-B hepatitis, blood transfusions are no longer a source for HCV transmission in Sweden. Anti-HCV testing was implemented for all blood donations in 1992. Since then intravenous drug use (IDU) has become the major route of transmission in the western world. Six genotypes and more than 80 subtypes of HCV have now been identified world-wide. These genotypes and subtypes are determined by genetic divergences between the HCV strains. Subtypes 1a, 1b, 2b, 2c, and 3a have global spread, while the other subtypes have a more limited geographical distribution. Little was known on the prevalence of HCV among blood donors and on which genotypes and subtypes of HCV were circulating in Sweden before the testing of all blood donations was implemented. The prevalence of anti-HCV was therefore investigated in sera sent to the Swedish Institute for Infectious Disease Control (SMI) from 412 patients; 241 were sampled between 1970 and 1991 before the universal screening in 1992, while 171 were sampled between 1992 and 2002. The samples derived from 193 (47%) blood donors, (104 sampled before, and 89 after 1992), and from seven other groups of patients. Two groups had suspected known routes of infection, intravenous drug use (IDU) 33 patients and hemodialysis, 16 patients, while it was unknown for the other patients. Anti-HCV was detected in 120 (29%) samples. The highest frequency was found among IDUs, (91%). Before general screening was implemented, 2.8% of the blood donors were positive for hepatitis C, whereas 28% of those sampled after 1992 were anti-HCV positive. Those latter samples were sent to SMI due to anti-HCV reactivity in a primary test at the blood centre. HCV RNA could be detected by PCR in 56 (47%) of the anti-HCV positive samples, the subtype could be determined by sequencing in 45 (80%) of those. The subtypes found were 1a in 31 %, 1b in 18%, 2b in 22%, and 3a in 27%. One sample was of subtype 2c. There was a tendency of increase of genotype 2 and a decrease in subtype 1a with time. 1a was found in 38% of the samples collected before 1992, while it was only found in 19% of the samples from 1992 or later. On the other hand genotype 2 was found in 17% sera sampled before 1992 and in 37% of the samples collected 1992 or later. It is not known if this genotype has recently been introduced into Sweden. Further analysis on larger series of samples is needed to confirm these preliminary results.