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Hepatitis B

Epidemiology of Infectious Diseases: Hepatitis B

Causal agent
Hepatitis B virus (HBV), a hepadnavirus.

Common clinical features

  • Many infections with HBV are asymptomatic or range from mild symptoms to fulminant hepatitis with fatigue, abdominal pain, loss of appetite, intermittent nausea, vomiting and jaundice.
  • The development of chronic HBV infection is age dependant, with young children more likely to develop chronic infection.
  • Chronic infection occurs in approximately 90% of infants infected at birth, between 30% - 50% of children infected at age 1-5 years and among 10% of adults1.
  • The risk of death from HBV related liver cancer or cirrhosis is approximately 25% for persons who become chronically infected during childhood.

Epidemiology

  • Hepatitis B virus (HBV) is a major global public health problem accounting for up to 1 million deaths per year.
  • The WHO estimates that approximately 2 billion people have been infected worldwide of which over 350 million are chronic carriers.
  • Hepatitis B is endemic in many developing countries particularly in Asia, Sub-Saharan Africa and the Pacific.
  • In Europe and North America HBV infection is relatively rare. In areas of low endemicity, most HBV infections are acquired by horizontal transmission in early adult life, particularly through sexual contact and intravenous drug use.

Reservoir
Humans 

Mode of transmission

  • Through direct contact with the bodily fluids of an infected person; blood, saliva, semen, vaginal secretions and to a lesser extent in breast milk, tears and urine.
  • The concentration of HBV is highest in blood.
  • In areas of high endemicity, the most common route of transmission is perinatal or is acquired in early childhood.
  • Common modes of transmission:  

Perinatal transmission
Sexual transmission
Close household contact
Intravenous drug use
Child to child transmission
Contaminated needles or syringes
Skin penetrating procedures including acupuncture, body piercing and tattooing.
Needle stick injuries.

The HBV virus is 50-100 times more infectious than HIV.

Incubation period
45-180 days, average 60-90 days

Period of Communicability
All persons who are HBsAg-positive are potentially infectious. The infectivity of chronically infected individuals ranges from high to modest.

Prevention and control
Provide advice and immunization to overseas travellers.

HBV prophylaxis for reported exposure incidents3.

 

References

  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
  2. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.
  3. CDSC. Exposure to hepatitis B virus; guidance on post-exposure prophylaxis. Commun Dis Review [serial online] 1992 [cited 14 August];2(9): Available at http://www.hpa.org.uk/cdr/archives/CDRreview/1992/cdrr0992.pdf

© CM Kirwan 2006