Hepatitis: Definition and Epidemiology

00:00 In our discussion of Gastrointestinal Tract Infections, we turn now to Hepatitis. You could define hepatitis as some kind of hepatocellular injury caused by one of these hepatotropic viruses: A, B, C, D or E. Let's talk some about the epidemiology first of hepatitis A. This viral infection has a worldwide distribution, it is spread person to person like close contact with the person or it can be spread by foodborne or waterborne methods. It is endemic in countries with poor hygiene and poor sanitation. Because of that, most people are infected by the age of 10. In developed countries, about 30% of us are infected by the age of 50. Hepatitis B is a different story. One-third of the world population had been infected at some point in their lives and the prevalence is greater than 8% in Asia, Africa and the Western Pacific, 2 to 7% in Southern and Eastern Europe but less than 2% in Western Europe, North America and Australia.

01:34 There are 400 million people who have a chronic hepatitis B infection and the carrier rate in children is significantly greater than that of adults. In other words, children are chronically infected and it probably because they get infected at a very early age when their immune system is not fully mature and when your immune system is fully mature that's what gets rid of the cells that have hepatitis B in them. So if you have an immature system, then you don't get rid of all the infected cells. Hepatitis C affects 3.6 million people in America. Look at the difference in percentage, 2.7 of those 3.6 have chronic hepatitis C. So the incidence of chronic hepatitis with C is tremendous. There is, however, a substantial decrease in the annual instance of new infection since we've began to learn about this. For example, in the mid 1980s there were 230,000 cases per year and presently 17,000 cases per year. There are about 15 million people in the world who are infected with hepatitis D and that includes 5% of 300 million hepatitis B virus infected persons and that's because hepatitis D is dependent on the presence of hepatitis B. 20 to 40% are infected in Central America, the Middle East and the Mediterranean Basin. It's uncommon surprisingly in Southeast Asia in China and in western countries it's almost exclusively found in intravenous drug users. Hepatitis E fairly recently discovered as a zoonotic disease. It accounts for 30 to 60% of sporadic hepatitis in India more than hepatitis A virus. So this is a common problem. Almost 20% mortality occurs in a woman who gets hepatitis E when pregnant, very serious.