People who inject drugs (PWIDs) are increasingly becoming a public health concern in various parts of the world. It is estimated that between 11 and 21.1 million people inject drugs worldwide. This group of people is therefore considered a high-risk group mainly for Hepatitis C virus transmission since they act as a bridge of infection to the general population. Epidemiologically, the seven recognized genotypes (1-7) of HCV exhibits high genetic diversity, characterized by regional variations in genotype, posing a challenge to vaccine development and HCV treatment which in many countries is still genotype-specific. This cross-sectional study aimed to determine the prevalence of Hepatitis C and the circulating genotypes among PWIDs in Nairobi County. The snowball sampling technique was used to recruit 212 participants from two drop-in centers in Nairobi who consented to participate in the study. Up to 5 mL of blood was collected. The blood samples were screened using Bio-Elisa HCV 4.0 kit to determine the serostatus of the samples. Sero-positive samples were subjected to molecular analysis by amplifying the nucleic acids using PCR, where detecting the desired region was done by gel electrophoresis and finally sequencing analysis to determine the genetic diversity of the circulating strains. Socio-demographic characteristics, including individual parameters such as age, gender, and behavior on needle use, were determined using a questionnaire that was administered during recruitment. Summaries on socio-demographics were presented using descriptive statistics and multi multivariate analysis was performed to determine the association between the socio-demographic characteristics and the presence of anti-HCV in the selected population (P< 0.05 was considered significant). The Neighbor-Joining method on the MEGA6 programmer was used to generate a bootstrap consensus phylogenetic tree out of 1000 bootstrap replicates. For results, a total of 212 PWID were successfully recruited for the study, out of whom 29(13.7%) tested seropositive, with males accounting for 72.4% (n=21) and females were 27.6% (n=8). Age (OR=15; P=0.09), duration of injecting drugs (OR= 11.38; P=0.001), and the frequency of injecting drugs (OR=0.28; P=0.042) were found to be significantly associated with HCV infection. Of the 29 seropositive samples, 27(93.1%) were PCR-positive and were used for genotypic identification. The HCV circulating strains detected were genotype 1 at 51.8% (n=14), genotype 4 at 14.8% (n= 4), genotype 6 at 14.8% (n=4) genotype 5 at 7.4% (n=2), genotype 3 at 3.7% (n=1) and undefined genotypes at 7.4% (n=2). The study concludes that there is a potential emergence of circulation of foreign strains in Nairobi demonstrated by the identification of genotypes 5 and 6 which are not known to circulate in the region and the presence of the 2 unidentified genotypes. This calls for a change of treatment strategy from genotype-specific therapy to pangenotype therapy. The study recommends further genotype characterization with a larger number of samples to establish the magnitude of circulation of the genotypes considered not found in the region. These will influence policy on treatment strategy for HCV infection which is considered genotype-specific.

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