Epidemiology

The hepatitis B virus is globally distributed among humans. The various strains of HBV are quite species specific. Though HBs has been found in other primates, humans remain the principal reservoir. ⁽¹⁾ Many individuals are affected worldwide, but the prevalence of HBV has been decreasing in developed countries, thanks to the availability of the hepatitis B vaccine, increasing knowledge of how the virus is spread as well as screening of donated blood before use.

The hepatitis B virus is primarily found in the blood of infected individuals. Virus titres, as high as ten billion virions per millilitre of blood, have been reported in HBe-positive carriers. However, HBV has also been detected in other bodily fluids including urine, saliva/nasopharyngeal fluids, semen, and menstrual fluids. ^{(2), (3)} This virus has not been detected in feces, perhaps due to inactivation and degradation within the intestinal mucosa or by the bacterial flora. ⁽⁴⁾

Transmission of HBV is done most efficiently via percutaneous introduction (i.e. needlestick injury). Sexual transmission is also possible though inefficient. There are other potential routes of transmission, but their efficiency is not easily measured. Children of mothers with active HBV are also at risk of acquiring HBV. Uninfected individuals living with an HBV carrier are at greater risk of contracting HBV than those not living with a carrier. This is likely due to the fact that HBV can survive even on a dry surface for over a week. ⁽⁵⁾ However, it should be remembered that for HBV to infect, it still must gain entry into the bloodstream of an uninfected individual.

Higher Risk Groups

• Individuals living in close proximity to a known infected individual,
• Users of intravenous drugs, particularly those who share their needles,
• Individuals who have multiple sexual partners,
• Health care workers (i.e. doctors, dentists, paramedics, nurses, etc.),
• Cleaning staff in health care facilities,
• Staff of institutions for people with developmental disabilities,
• Firefighters,
• Police Officers,
• Mortuary attendants,
• Daycare workers, and
• Anyone who may/has come into contact with human bodily fluid from an unknown or known HBV carrier source.

References:
1. Mosley, J.W. 1975. The Epidemiology of Viral Hepatitis: An Overview. Am J Med Sci; 270: 253-270.

2. Alter, H.J., Purcell, R.H., Gerin, J.L. et al. 1977. Transmission of Hepatitis B Surface Antigen-Positive Saliva and Semen. Infect Immun; 16: 928-933.

3. Davison, F., Alexander, G.J.M., Trowbridge, R., Fagan, E.A. and Williams, R. 1987. Detection of Hepatitis B Virus DNA in Spermatozoa, Urine, Saliva and Leucocytes of Chronic HBsAg Carriers. Hepatology; 4: 37-44.

4. Grabow, W.O.K., Prozesky, O.W., Applebaum, P.C. and Lecatsas, G. 1975. Absence of Hepatitis B Antigens from Feces and Sewage as a Result of Enzymatic Destruction. J Infect Dis; 131: 658-664.

5. Bond, W.W., Favero, M.S., Petersen, N.J., Gravelle, C.R., Ebert, J.W., Maynard, J.E. 1981. Survival of Hepatitis B Virus After Drying and Storage for One Week. Lancet; 1: 550-551.