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S8 Epidemiology and Natural History of Hepatitis C. D. THOMAS*. Johns Hopkins Med. Inst., Baltimore, MD.
Percutaneous exposure to contaminated blood is sufficient to transmit hepatitis C virus (HCV), as proven by experimental infection of chimpanzees and accidental inoculation of humans. Accordingly, a high HCV prevalence is found among persons with blood exposures such as injection drug users, and most persons who acquire HIV infection from contact with blood also have hepatitis C. Worldwide, nosocomial percutaneous practices are the chief route of HCV transmission. In the US, it is injection drug use.
Whether percutaneous exposure to blood is necessary for HCV transmission is controversial. HCV RNA has been detected in genital fluids and HCV infection occurs more often in persons with high risk sexual practices. However, most long-term monogamous partners of HCV infected persons remain uninfected. Resolution of this uncertainty requires development of experimental models of transmission and instruments to measure illicit drug use. Mother to infant HCV transmission uncommonly occurs; the mechanism and timing are unknown.
HCV infection can be self-limited, persist without symptoms, or cause liver failure. HCV infection is considered self-limited when HCV RNA is not detected in blood on multiple occasions, an outcome that appears to occur less often in Blacks, persons infected at older ages, and those with HIV infection. The biologic basis for clearance of HCV RNA from blood is unknown.
HCV infection usually persists without causing symptoms, but after 20 years, may cause cirrhosis in 2-20% of those infected. The development of cirrhosis cannot be predicted by noninvasive testing such as ALT level, HCV viral load, or genotype. Alcohol use and HIV co-infection increase the occurrence of cirrhosis.
HCV infection is usually acquired by percutaneous exposure to blood and typically persists for more than 20 years without causing illness. Additional research is needed to demonstrate the mechanisms of transmission, how to prevent infection, and the biologic basis for viral clearance and cirrhosis.
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