Hepatitis B: epidemiology

The main reservoir and source of HBV are patients with acute hepatitis B. patients with chronic HBV infection (virus carriers and patients with CHB), the number of which on the globe exceeds 300 million people.

In patients with HBV infection, HBsAg and HBV DNA are found in the blood, urine, saliva, bile, tears, feces, breast milk, vaginal secretions, sperm, cerebrospinal fluid, and umbilical cord blood. However, only blood, sperm, and possibly saliva pose a real epidemiological hazard, since the concentration of the virus in other fluids is very low. The main transmission factor is blood. An infective dose of the virus can be contained in 0.0005 ml of blood. Viral hepatitis B is characterized by multiple transmission routes (natural and artificial): contact, vertical, and artificial (parenteral manipulations, organ transplantation) transmission routes are possible. Sexual transmission of HBV is extremely effective. Among those infected with the hepatitis B virus, the proportion of drug addicts who practice intravenous drug use is high. In this regard, even in highly developed countries, the significant infection rate of drug addicts, as well as homo- and heterosexuals with a large number of sexual partners, maintains a high epidemic potential of HBV infection. Infection with viral hepatitis B is also possible through everyday contact with a sick person or a virus carrier when the integrity of the mucous membranes and skin is compromised. In these cases, HBV is introduced through damaged skin (microtrauma), through direct contact with the source of infection, or through the shared use of various household and personal hygiene items (blood-contaminated linen, scissors, nail files, toothbrushes, razors, washcloths, etc.). Of particular importance is the vertical transmission of HBV from a pregnant woman (sick with acute hepatitis B or chronic HBV infection) to the fetus or newborn. In this case, transplacental transmission of the virus is possible (about 8% of cases among infected children) or, more often, infection during childbirth when the newborn comes into contact with infected amniotic fluid, vaginal secretions. The risk of infection increases significantly if acute hepatitis B develops in a woman in the third trimester of pregnancy and childbirth occurs during the period of HBeAgemia or the child is born to a woman with chronic hepatitis B with the presence of HBeAg in the blood.

Currently, the risk of infection during blood transfusion has decreased dramatically, since all donor blood is tested for the presence of HBcAg and anti-HBcIgG. Infection with viral hepatitis B is possible with various parenteral medical and non-medical interventions accompanied by a violation of the integrity of the skin or mucous membranes (injections, dental, endoscopic, gynecological examinations, cosmetic procedures, piercing, tattooing, etc.), if the rules for sterilization of instruments are violated. Risk groups for infection with viral hepatitis B include patients in hemodialysis departments, burn centers, hematology, tuberculosis hospitals, cardiovascular surgery centers, medical workers who have contact with blood: procedural and surgical nurses, anesthesiologists-resuscitators, obstetricians-gynecologists, surgeons, dentists, etc. Susceptibility to viral hepatitis B is high. Age-related susceptibility to viral hepatitis B has a number of features, mainly related to the probability of chronicity of the infection. The risk of developing chronic HBV infection after infection with the hepatitis B virus ranges from 90% in newborns born to HBeAg-positive mothers to 25-30% in infants and children under 5 years of age and is less than 10% in adults. Immunity after viral hepatitis B is long-term, possibly lifelong. Repeated cases of viral hepatitis B are observed extremely rarely.

The prevalence of hepatitis B (including the incidence of acute forms and the percentage of virus carriers) varies significantly in different regions of the world. The prevalence assessment criterion is the frequency of HBsAg detection among the healthy population (donors). Regions with a carriage frequency of less than 2% are considered to be low prevalence, 2-7% - average, and more than 7% - high. In Australia, Central Europe, the USA, and Canada, a low carriage rate (no more than 1%) is noted, and in Southeast Asia, Southern China, Taiwan, and tropical Africa, 20-50% of the population are HBsAg carriers. The proportion of people aged 15-29 years is 60-85% of the total number of patients with acute hepatitis B, which is associated with the prevalence of injection drug addiction and risky sexual behavior without the use of barrier methods of contraception.

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