Friday, October 21, 2011

Healthcare workers acquired hepatitis C virus

HCV is a small, enveloped, single-stranded, positive sense RNA virus. There are six major genotypes of the HCV, which are indicated numerically (e.g., genotype 1, genotype 2, etc.) (Tarantola et al., 2006).
HCV is not transmitted efficiently through occupational exposures to blood. The average incidence of anti-HCV sero-conversion after accidental percutaneous exposure from an HCV-positive source is 1.8% (range: 0%–7%). Transmission rarely occurs from mucous membrane exposures to blood and no transmission in HCWs has been documented from intact or non-intact skin exposures to blood. Data are limited on survival of HCV in the environment. In contrast to HBV, the epidemiologic data for HCV suggest that environmental contamination with blood containing HCV is not a significant risk for transmission in the healthcare setting (Manns et al., 2007).

Laboratory diagnosis:
Hepatitis C testing begins with serological blood tests used to detect antibodies to HCV. Anti-HCV antibodies can be detected in 80% of patients within 15 weeks after exposure, in >90% within 5 months after exposure and in >97% by 6 months after exposure. Overall, HCV antibody tests have a strong positive predictive value for exposure to the hepatitis C virus, but may miss patients who have not yet developed antibodies (seroconversion), or have an insufficient level of antibodies to detect (Watanabe et al., 2003).
Rarely, people infected with HCV never develop antibodies to the virus and therefore, never test positive using HCV antibody screening. Because of this possibility, RNA testing should be considered when antibody testing is negative but suspicion of HCV is high (e.g. because of elevated transaminases in someone with risk factors for HCV) (Scott et al., 2006).
Anti-HCV antibodies indicate exposure to the virus, but cannot determine if ongoing infection is present. All persons with positive anti-HCV antibody tests must undergo additional testing for the presence of the HCV itself to determine whether current infection is present. The presence of the virus is tested by using molecular nucleic acid testing methods such as PCR, transcription mediated amplification (TMA), or branched DNA (b-DNA) (Watanabe et al., 2003).
Determining the ALT level is useful for monitoring the effectiveness of therapy for HCV infection. Because ALT levels can fluctuate, a single value in the reference range does not rule out active infection, progressive liver disease, or cirrhosis. ALT normalization with therapy is not proof of cure (Watanabe et al., 2003).

Fig. (1): Diagnosis of HCV (Watanabe et al., 2003).

Genotyping is helpful for predicting the likelihood of response and duration of treatment. Patients with genotypes 1 and 4 are generally treated for 12 months, whereas 6 months of treatment is sufficient for other genotypes. Genotyping can be performed by direct sequence analysis, reverse hybridization to genotype-specific oligonucleotide probes or restriction fragment length polymorphisms (Manns et al., 2007).

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