chronic infection. The CDC (2016b) estimated nearly 18,100 cases of acute hepatitis B in the United States in 2014. This is a substantial decline since vaccination was introduced in the 1980s.
he hepatitis B virus is transmitted by exposure to blood or body fluids from infected individuals. In endemic countries, vertical transmission, that is, from mother to fetus or newborn, accounts for at least 35 to 50 percent of chronic HBV infections. In low-prevalence countries such as the United States, which has a prevalence <2 percent, the more frequent mode of HBV transmission is by sexual transmission or by sharing contaminated needles. HBV can be transmitted in any body luid, but exposure to virus-laden serum is the most eicient.
Acute hepatitis B develops after an incubation period of 30 to 180 days with a mean of 8 to 12 weeks. At least half of acute infections are asymptomatic. If symptoms are present, they are usually mild and include anorexia, nausea, vomiting, fever, abdominal pain, and jaundice. Acute HBV accounts for half of cases of fulminant hepatitis. Symptoms completely resolve within 3 to.4 months in more than 90 percent of patients.
Figure 55-2 details the sequence of the various HBV antigens and antibodies in acute infection. The first serological marker to be detected is the hepatitis B surface antigen (HBsAg) , often preceding the increase in transaminase levels. As HBsAg disappears, antibodies to the surface antigen develop (anti-HBs), marking complete resolution of disease. Hepatitis B core antigen is an intracellular antigen and not detectable in serum. However, anti -HBc is detectable wi thin weeks of HBsAg appearance. The hepatitis Be antigen (HBeAg) is present during times of high viral replication and often correlates with detectable HBV DNA. After acute hepatitis, approximately 90 percent of adults recover completely. The 10 percent who remain chronically infected are considered to have chronic hepatitis B.
Chronic HBV infection is oten asymptomatic but may be clinically suggested by persistent anorexia, weight loss, fatigue, and
FIGURE 55-2 Sequence of various antigens and antibodies in acute hepatitis B. ALT = alanine transaminase; anti-HBc = antibody to hepatitis B core antigen; anti-HBe = antibody to hepatitis Be antigen; anti-HBs = antibody to hepatitis B surface antigen; HBeAg = hepatitis Be antigen; HBsAg = hepatitis B surface antigen. (Reproduced with permission from Dienstag JL: Acute viral hepatitis. In Kasper DL, Fauci AS, Hauser SL, et al (eds): Harrison's Principles of Internal Medicine, 19th ed. New York, McGraw-Hili Education, 201o5).