Nephrol Dial Transplant. center, 5 of the 20 patients were HCV RNA positive, and two HVR1 sequences were found to be closely related and phylogenetically derived from the same cluster. The antibody responses of these patients to the HVR1 peptides representative of the genetic clusters revealed exactly the same clustering as that shown by phylogenetic analysis. These findings suggest that phylogenetic and serological analyses of HVR1 sensitively detect unrecognized and multiple transmission of HCV occurring within the same room in hemodialysis centers. Fingerprinting analyses using hypervariable regions of infectious brokers are useful in identifying the precise route of transmission of contamination. Hepatitis C computer virus (HCV) is a major causative agent of posttransfusion non-A, non-B hepatitis. Screening and confirmatory assays for circulating antibodies to HCV became available (10, 27) after the molecular cloning of the HCV genome in 1989 (3). The second-generation enzyme immunoassay for detection of anti-HCV antibody has revealed a high prevalence of antibodies to HCV in hemodialysis (HD) patients (5). Most cases of HCV contamination in HD patients are thought to be related to blood transfusions, but several reports from different parts of the world have also shown the presence of HCV contamination in nontransfused HD patients as well (8, 22, 30), and the anti-HCV antibody-positive rates have been found to increase with the duration of dialysis (8, 22, 30). This suggests that SB 202190 nosocomial transmission of HCV occurs in HD models. Recently, patient-to-patient transmission of HCV in HD models has been exhibited by molecular biology techniques, but the frequency of transmission was low (2, 20, 25). In these studies the sequences of HCV dominantly propagating in patients were decided and compared. Allander et al. (2) were the first to detect nucleotide sequence similarity in variable parts of the HCV genome in several HD patients. Sampietro et al. (20) and Stuyver et al. (25) found a rare HCV variant in several patients treated in the same HD unit by sequencing the relatively conserved region of the HCV genome, the 5 untranslated region (5-UTR), and the core region, respectively. However, no evidence of transmission had ever been exhibited by sequence analysis of a minor populace of HCV isolates. The HCV genome exhibits different variability of nucleotide sequences in different regions. There is a hypervariable region, hypervariable region 1 (HVR1), in the putative second envelope glycoprotein (E2) of the HCV genome (7). HVR1 consists of 27 amino acid residues located in the N-terminal region of E2 and is the most variable region in the HCV genome. Accordingly, it appeared that HVR1 might be useful for discriminating HCVs the same as a polymorphic marker for genetic fingerprinting and for detecting nosocomial transmission of HCV. It was thought that not only rare but also common genotypes of HCV might be found to be transmitted. Furthermore, most patients with chronic hepatitis C possess antibody against the HVR1 of their own isolates (9, 29), and anti-HVR1 antibody was also thought to be useful for demonstrating nosocomial transmission. In this study, we examined HCV SB 202190 transmission in HD models by performing phylogenetic analysis of HCV HVR1 sequences and testing for antibodies to HVR1 peptides. We also analyzed multiple sequences of HVR1 from each individual and investigated nosocomial transmission of HCV, including a minor populace of HCV isolates transmitted in HD patients. MATERIALS AND METHODS Patients. We studied patients attending two dialysis centers. In one dialysis center, 62 patients were examined for HCV RNA twice, once in October 1994 and again in April 1996, by a two-step PCR amplifying the 5-UTR. Nine patients were positive for HCV RNA the first time they were examined and two additional patients were found to be positive the second time. A total of 20 samples of patient serum were used for the sequence analysis of HCV HVR1 and the assay for anti-HVR1 CSF1R antibody. Serial samples of serum from the patients were tested for alanine aminotransferase (ALT) and anti-HCV antibodies with a second-generation enzyme-linked immunosorbent assay (ELISA) (ELISA II; Ortho Diagnostic Systems, Tokyo, Japan). In the other center, 5 of the 20 patients were found to be positive for HCV, and their HCV HVR1 sequences were then examined. The HCV isolates from all patients were genotype 1b as determined by the SMI TEST HCV-Genotype (Sumitomo Metal Industries, SB 202190 Tokyo, Japan). All dialysis machines in each center were located in a single room. All patients were hemodialyzed against standard bicarbonate dialysate three times weekly, for 4.