Hepatitis C virus (HCV) isolates have been divided into six genotypes (1 to 6). The duration of hepatitis C standard treatment is 48 weeks for patients infected with HCV genotype 1 vs 24 weeks for those infected with genotypes 2 and 3. A total of 1544 HCV isolates from chronic patients living in the southern Brazilian states of Rio Grande do Sul (RS, n = 627) and Santa Catarina (SC, n = 917) were genotyped by restriction fragment length polymorphism (RFLP) of polymerase chain reaction (PCR) products. In RS, 338 (53.9%; 34 (5.4%; 255 (40.7%;.6%) samples were from genotypes 1, 2, and 3, respectively. In SC, 468 (51%; 26 (2.9%; 423 (46.1%;
samples were from genotypes 1, 2, and 3, respectively. Genotyping results were confirmed by direct nucleotide sequencing of PCR products derived from 68 samples, without any discrepancy between PCR-RFLP and nucleotide sequencing methods. In conclusion, almost half of the hepatitis C patients from South of Brazil are infected by genotypes 2 and 3 and, these results have important consequential therapeutic implications as they can be treated for only 24 weeks, not 48.Key words: hepatitis C virus genotypes -polymerase chain reaction -restriction fragment lengh polymorphismnucleotide sequencing -Rio Grande do Sul -Santa CatarinaChronic hepatitis C, caused by infection with hepatitis C virus (HCV), is a global health problem, with more than 170 million infected individuals worldwide (WHO 1999). In 15 -20% of acute HCV infections, the patients recover spontaneously. However, in a large majority of cases, the disease runs a chronic course, clinically silent. Persistent infection may lead to severe liver diseases, such as cirrhosis and hepatocellular carcinoma, which require intensive treatment regimens and, in some cases, liver transplantation, and long-term care.HCV is primarily transmitted by the parenteral route. Sexual and perinatal transmissions have also been demonstrated, although less frequent (Poupon 2005). Since there is no available vaccine against hepatitis C, the only means to lower the disease burden are prevention of new infections and treatment of chronic carriers.HCV has a large genetic heterogeneity. Virus isolates have been classified into six genotypes (1 to 6), based on nucleotide sequence divergence of 30 -35% (Simmonds 2004). Genotypes 1, 2, and 3 circulate around the world, while genotypes 4, 5, and 6 are restricted to determined geographical areas (McOmish et al. 1994). In Brazil, genotypes 1, 2, and 3 predominate, although genotypes 4 and 5 have also been found (Campiotto et al. 2005).HCV genotype determination is necessary to define the optimal duration of therapy and the likelihood of response. According to the European Association for the Study of the Liver (EASL 1999) International Consensus Panel and National Institutes of Health (NIH 2002) Consensus Panel on management of hepatitis C, standard therapy for chronic HCV infection is based on combination of pegylated interferon (PEG IFN) alfa-2a or alfa-2b with ribavirin (RBV) during 48 weeks for patie...