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DISTRIBUTION OF DISEASE

Geographic Distribution

The disease burden of hepatitis B varies significantly in different parts of the world. The combined total of chronic carriers and healthy immune individuals provides a good measure of the rate of infection. Using this measure, the world can be divided into areas of high infection rate (sub-Saharan Africa, east Asia, and the Pacific Islands), moderate infection rate (Middle East, central Asia, South America, eastern Europe, and Arctic), and low infection rate (North America, western Europe, and Australia) (Francis, 1983).

Lack of surveillance and lack of serologic testing hamper quantitation of disease incidence in many of the high-rate areas. Nevertheless, available estimates demonstrate the enormity of the problem.

Acute HBV manifestations are relatively less common in endemic countries than in other areas because much of the disease burden occurs during childhood, when symptoms are less frequent. However, the total burden of acute disease is large in these countries because the disease is so widespread.

The total disease burden resulting from HBV in endemic areas is large because of the high infection rates at early ages, with the late sequelae that result from persistent infection. For example, the incidence of primary hepatocellular carcinoma in many areas of the world exceeds the incidence of acute hepatitis B in the United States (Maupas and Melnick, 1981).

The largest number of HBV infections occurs in China (60 million HBV carriers). Actual mortality rates in China have been reported for primary hepatocellular carcinoma (PHC) (Armstrong, 1980). The rate is extremely high in southeast China (50 to 60 per 100,000 per year). Throughout China, the rate is reported to be about 20 per 100,000 per year (Francis, personal communication, 1984). Less information is available on cirrhosis deaths, but a Taiwanese study found that there were 0.43 deaths from HBsAg-positive cirrhosis for every PHC death (Beasley et al., 1981). Complete data are not available for acute hepatitis B in China, but the annual incidence is estimated to be about 700,000 cases, and half of the infectious disease beds are occupied by hepatitis patients (over half of which are HBV-related).

Disease Burden Estimates

The disease burden estimates include three major disease states: acute hepatitis B, primary hepatocellular carcinoma, and cirrhosis.

Acute Hepatitis B

Cases and deaths due to acute hepatitis B were calculated as shown in Table D-5.1.



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