Hepatitis B infection is widespread all over the world, and the epidemic intensity of HBV infection varies greatly in different regions. According to the report of the World Health Organization, there are about 2 billion people infected with HBV in the world, of which 350 million are chronic infections, and about 65.438+0 million people die of liver failure, cirrhosis and primary liver cancer (HCC) caused by HBV infection every year.
In 2006, the national survey of hepatitis B epidemic virus showed that the HBsAg carrying rate of people aged 1-59 in China was 7. 18%, and the HBsAg carrying rate of children under 5 years old was only 0.96%. According to this calculation, there are about 93 million chronic HBV-infected people in China, among which about 20 million active hepatitis B patients need symptomatic treatment.
Hepatitis B is a blood-borne disease, which is mainly transmitted through blood (such as history of unsafe injection), mother-to-child transmission and sexual transmission, as well as a certain proportion of skin and mucous membrane injuries, such as tattoos, ear piercings and endoscopy. Blood products are strictly controlled, and the possibility of transmission is greatly reduced, which will only happen if blood transfusion and blood products are not standardized. Accidental exposure in medical staff's work can not be ignored. With the vigorous promotion of neonatal hepatitis B vaccine and the implementation of other mother-to-child blocking measures, mother-to-child transmission has been greatly controlled. At present, about 90% HBV-DNA positive mothers have successfully blocked the vertical transmission from mother to child through intervention. HBV infection will not spread through respiratory tract and digestive tract, so you will not be infected with HBV in your daily study, work or life, like the same office (sharing office supplies such as computers), living in the same dormitory, eating in the same restaurant, hugging, shaking hands, sharing toilets, etc. Epidemiological and experimental studies have not found that hepatitis B can be transmitted through the bites of blood-sucking insects such as mosquitoes and bedbugs.
The age when infected with hepatitis B virus is the most important factor that causes chronic hepatitis B. In perinatal period (that is, within 42 days after the mother gave birth) and infancy, 90% and 25% ~ 30% of HBV infection developed into chronic infection, while only 5% ~ 10% of HBV infection developed into chronic infection after 5 years old, and then developed into chronic hepatitis B after being infected with hepatitis B in infancy. Its natural history is generally divided into four periods: immune tolerance period, immune clearance period, inactivated replication period and reactivation period. The characteristics of each stage are as follows: ① Immune tolerance stage: HBsAg, HBeAg and anti-HBC are positive in serum (that is, the three major positive), and the HBV-DNA virus load is high, but the liver function is normal, and there is no obvious liver injury by liver histological examination, which can last for several years or even decades. ② immune clearance period: in this period, the serum can be HBsAg, HBeAg, anti-HBC (big three positive), HBsAg, anti-HBe and anti-HBC (small three positive), and the quantitative detection of virus (HBV-DNA) is generally greater than 2000IU/ml (equivalent to 104copies/ml), accompanied by repeated abnormalities of liver function (such as ALT). ③ Inactive replication period: HBsAg, anti -HBe, anti -HBC (small three positive) and HBV-DNA are below the detection limit, the liver function is normal, and there is no or slight damage to liver histology, which indicates that hepatitis B is controlled by the internal immune system, and the risk of cirrhosis and liver cancer is greatly reduced during this period. ④ Recurrent period: Some patients in inactive period may have recurrent hepatitis activity under certain incentives, such as DNA positive conversion, abnormal liver function and aggravation of illness. These causes include fatigue, decreased immunity, use of immunosuppressants or cytotoxic drugs. Especially those patients with chronic hepatitis B who are still positive for HBV-DNA are more prone to recurrent hepatitis attacks, and their condition may develop into liver fibrosis, cirrhosis and even HCC (primary liver cancer).