4 Hepatitis Viruses
At the time of writing, at least six viruses are known to cause hepatitis: hepatitis A, B, C, D, E, and G. Epidemiologically, the viruses can be divided into two groups according to mode of transmission. The hepatitis A and E viruses are transmitted primarily by the fecal-oral route. The hepatitis B, C, D, and G viruses are transmitted by direct contact with blood or body fluids. Hepatitis B and C viruses are frequently responsible for occupational infections.
4.1 Hepatitis B Virus (HBV)
Hepatitis B virus is transmitted parenterally, sexually, and perinatally, and is the major cause, worldwide, of acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. High risk groups in industrialized countries include intravenous drug users, homosexual men, and those with multiple sexual partners (113). Others at substantial risk of infection include hemodialysis patients, institutionalized patients, and healthcare workers with occupational exposure to blood (114).
Healthcare personnel have been known to be at greater risk for HBV infection than the general population (115, 116). The incidence of clinical cases of hepatitis B in healthcare workers before the availability of the hepatitis B vaccine (i.e., before 1982) was reported to be between 50 and 120 per 100,000 (117, 118), much higher than that of the general population of <10 cases per 100,000 (114). Level of risk was related to several factors, including the frequency of exposure to blood, body fluids, or blood-contaminated sharps; the duration of employment in a high risk occupation where blood exposure was common; and the underlying prevalence of HBV infection in the patient population. High prevalence of infection was found in occupations associated with the emergency department, laboratory, blood bank, intravenous team, and the surgical house officers (119).
Since 1982, changes in infection control practices, including the recommendation in 1987 of "universal precautions" (6), and the availability of the hepatitis B vaccine to at-risk workers have undoubtedly been responsible for the decline in the numbers of occupational hepatitis B infections (120). The proportion of reported hepatitis B cases associated with healthcare workers has declined from 4% in 1982 to 1% in 1988. The annual number of new HBV infections in healthcare workers has steadily declined from 12,000 in 1985 to 1000 in 1994 (121). Several reports from university hospitals confirm the decline after initiation of the hepatitis B immunization programs. Lanphear et al. (122) reported a decline in clinical hepatitis B in healthcare workers from 82 cases per 100,000 in 1980-1984 to no cases between 1985 and 1989. At Duke University, the number of cases of clinical hepatitis B in hospital employees has declined from 2 cases per 1000 in 1979 to none since 1992, with a vaccine acceptance rate of 90% (122a).
4.2 Hepatitis C Virus (HCV)
Choo et al. (123) discovered the hepatitis C virus (HCV) genome in 1989 and developed a serological test for the agent. Since then, HCV has been found to be the primary agent of parenterally transmitted non-A, non-B (NANB) hepatitis and a major cause of acute and chronic hepatitis throughout the world (124). High rates of HCV infection occur in intravenous (iv) drug users, where it has been estimated that two-thirds of addicts are anti-HCV seropositive within 2 years of regular use of IV drugs, increasing to close to 100% seropositivity after 8 years (125). Other groups at high or moderate risk include patients with repeated direct exposures to blood such as hemodialysis patients (126) and hemophiliacs (127). Lower rates are found in those with inapparent parenteral or mucosal exposures such as sexual contacts of infected persons (128) or transmissions from mother to infant (129). Blood transfusions have transmitted the virus. Before testing of the virus was available in 1989, the risk of HCV infection per unit was 0.45%; after antibody testing became available, 0.06% (130).
Although HCV transmission occurs in the healthcare setting, the seroprevalence rate in workers is only slightly higher than the corresponding general population. In general, most studies document an HCV seroprevalence of between 1 and 2.8% for healthcare workers compared with the rate of 0.31.5% in blood donors (the community rate) (131).
Prospective studies that record seroconversions after documented percutaneous exposures indicate the risk of HCV infection after a single injury to a healthcare worker can range from 0.75% (132) to 10% when PCR methodologies are used to determine HCV-RNA (133). The wide range of risk reflects the differences in study design, diagnostic tests used, number of cases followed, source patient status, and community prevalence. In general, after pooling data from 9 published prospective studies, a risk of 2.5% after a percutaneous injury is a reasonably accurate estimate (132).
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