Epidemiology - Hepatitis B Virus

Epidemiology

Hepatitis B is a major cause of infectious hepatitis worldwide.

◗ Geographical distribution

Hepatitis B virus is the leading cause of chronic hepatitis, cirrhosis, and hepatocellular carcinoma worldwide. Nearly, one-third of the world population is believed to be infected with HBV. More than 10% of people living in sub-Saharan Africa and in East Asia are infected with HBV. Approximately, 5–10 lakh persons die annually from HBV-related liver disease. An estimated 250,000 persons die from chronic HBV infection every year in the world. Estimates suggest that 400–500 million people worldwide are HBV carriers. The HBV carrier rate varies from 1% to 20% worldwide. This variation is due to difference in the age of infection and in the mode of transmission.

◗ Reservoir, source, and transmission of infection

Individuals with chronic HBV infection are the major reservoir of HBV infections. These people with HBeAg in their serum tend to have high viral titers and thus greater infectivity. Hepatitis B virus is present at a high level in serum. The virions are also present at very low levels in semen, vaginal mucosa, saliva, and tears, and all are infectious. The virus is not detected in urine, stool, or sweat; hence these specimens are not infectious. The hepatitis B virus can be transmitted in the following ways:

Perinatal transmission: This is the major route of transmis-sion of the virus worldwide. The transmission occurs from infected mother to child due to contact with mother’s infected blood during the time of delivery as opposed to transplacental passage of the virus. Although HBV is found in breast milk, the role of breast-feeding in transmission is unclear.

Parenteral transmission: This transmission occurs due totransfusion of HBV-infected blood and blood products. This was one of the important modes of transmission before 1970s, but with the starting of screening of blood donors for HBsAg, the rate of blood transfusion associated HBV infection has reduced considerably in India and other parts of the world. Patients with hemophilia, renal dialysis, and those receiving organ transplantation and intravenous drug users remain at increased risk of infection. The risk of acquiring HBV among health workers after needle stick injury from infected individu-als is estimated to be as high as 5%.

Sexual transmission of HBV: Hepatitis B virus is transmittedsexually more easily than Hepatitis C virus (HCV) or Hepatitis D virus (HDV). The infection is associated with vaginal inter-course, genital rectal intercourse, and nongenital intercourse. However, the HBV is not transmitted by hugging and kissing or by sharing towels, eating utensils, or food. Health workers with exposure to infected blood or body fluids, heterosexual persons with multiple partners, household contact, or sexual partners of HBV carriers are other groups at risk.