Molecular epidemiology of a hepatitis C virus outbreak in a hemodialysis unit

Abstract

We analyzed a hepatitis C virus (HCV) transmission case in the hemodialysis unit of a private clinic by sequencing two genome regions of virus isolates from a number of patients attending this unit and some external controls. The analysis of 337 nucleotides (nt) in the NS5B region did not provide enough resolution to ascertain which patients were actually involved in the outbreak and the potential source. Nevertheless, this region allowed the exclusion of several patients as putative sources of the transmission case based on their genotypes and phylogenetic relationships. On the other hand, the analysis of several 472-nt-long clone sequences per sample in a more rapidly evolving region of the HCV genome, coding for the envelope proteins and encompassing hypervariable region 1, allowed us to establish the existence of at least two independent transmission events involving two different source patients and three recipients. The direction of the transmissions was further corroborated by different measures of genetic variability within and among samples.

FIG.1.

Maximum-likelihood phylogenetic tree obtained for the NS5B regions of 14 samples analyzed in this study (identified by suffix VIN) and 51 unrelated sequences. Among the latter, there are two pairs of sequences (nbC05T0-nbC05T1 and nbG26T0-nbG26T1) which were derived from the same patients at two time points separated by a 6-month interval. Nodes with bootstrap support higher than 70% are indicated. The scale bar represents genetic distance (substitutions per site).

FIG. 2.

Maximum-likelihood phylogenetic tree obtained with 122 clone sequences from the E1-E2 region derived from the 10 samples with genotype 1b included in this study and 73 unrelated sequences. Among the latter, there are several pairs of sequences which were derived from the same patients at two time points separated by a 6-month interval (T0, T1, and T2). Monophyletic clusters of clone sequences are represented by filled triangles whose areas are proportional to the genetic diversity among the sequences included therein. The number of sequences is reported in parentheses after the corresponding sample name. See Fig. 3 for more details of the groups labeled A and B. Nodes with bootstrap support higher than 70% are indicated. The scale bar represents genetic distance (substitutions per site).

FIG. 3.

Detailed representation of portions of the maximum-likelihood tree for E1-E2 sequences depicted in Fig. 2. (Top) Group A, including clone sequences from samples 40, 41, and 43. (Bottom) Group B, including clone sequences from samples 39 and 42. In both cases, the sister branch has been included as a reference. Nodes with bootstrap support higher than 70% are indicated. The scale bar represents genetic distance (substitutions per site).