Epidemiology

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From 1965 to 1985, a progressive rise in reported hepatitis B cases occurred. Since then, the incidence of the disease has appeared to plateau and decline (figure 24.21). HBV is spread mainly by blood, blood products, and semen. Persisting viremia, meaning virus circulating in the bloodstream, can follow both symptomatic and asymptomatic cases, and the virus may continue to circulate in the blood for many years. Carriers are of major importance in the spread of hepatitis B because they are often unaware of their infection. If only a minute amount of blood from an infected person is injected into the bloodstream or rubbed into minor wounds, infection can result. Blood and other body fluids can be infec-

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1970 1975 1980 1985 1990 1995 2000 Year

Figure 24.21 Incidence of Viral Hepatitis in the United States Most of the non-A, non-B hepatitis is caused by hepatitis C virus.The first hepatitis B vaccine was licensed in 1982, the first hepatitis A vaccine in 1995. A test for hepatitis C antibody became available in 1990.

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1970 1975 1980 1985 1990 1995 2000 Year

Figure 24.21 Incidence of Viral Hepatitis in the United States Most of the non-A, non-B hepatitis is caused by hepatitis C virus.The first hepatitis B vaccine was licensed in 1982, the first hepatitis A vaccine in 1995. A test for hepatitis C antibody became available in 1990.

tious by mouth, the virus probably infecting the recipient through small scratches or abrasions. Many hepatitis B virus infections result from sharing of needles by drug abusers. Unsterile tattooing and ear-piercing instruments and shared toothbrushes, razors, or towels can also transmit HBV infections.

Sexual intercourse is responsible for transmission in nearly half of hepatitis B cases in the United States. HBV antigen is often present in saliva and breast milk, but the quantity of infectious virus and risk of transmission is low. Five percent or more of pregnant women who are HBV carriers transmit the disease to their babies at delivery, and more than two-thirds of women who develop hepatitis late in pregnancy or soon after delivery do so. Most of these babies have asymptomatic infections and become long-term carriers, but some die of liver failure.

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