Week 2: Epidemiology of Hepatitis B

According to the Bureau of Labor Statistics, the definition of Epidemiology is the scientific investigation into the “patterns and causes of disease and injury in humans.” With this as our beginning, we will look at the causes and the worldwide patterns/effects that Hepatitis B virus has displayed in today’s society.

The Hepatitis B virus has been found to only cause injury to humans. Primates have been infected in laboratory studies. However, the virus doesn’t appear to be able to survive in any of the host animals and has not been found to exist in any other species of animal or insect.  In the CDC’s Pink Book: Course textbook, they report “In the United States, the most important route of transmission is through sexual contact, either heterosexual or homosexual” (May 2012).  This is the main source of infection, although there are other sources as well. These sources include: mother to child transmission during the birth process, use of contaminated drug injection needles, and contact with infected blood or mucous membranes at the site of an opening (fresh cut, abrasion, burn or lesion) of the skin (paraphrased from CDC Pink Book, 2012, p120). We will next talk about what we have learned in each of these points of infection.

For reference as to what each of the various abbreviations you might come in contact with when looking into the hepatitis b literature, here is a key that you can use:

HBV: hepatitis B virus

Anti-HBs: antibody to hepatitis B surface antigen

HBeAg: hepatitis B e antigen

HBsAg: hepatitis B surface antigen

MSM: men who have sex with men (Shepard, 2006, p112)

When looking at the patterns of transmission for HBV, the global epidemiology has broken down into three categories of endemicity – high, intermediate, and low – depending on the proportion of the population that is seropositive for HBsAg (paraphrased from Shepard, 2006, p115). Each category of endemicity is identified as follows:

High = a seroprevalence of HBsAg is >/= 8 percent

Intermediate = a seroprevalence of HBsAg is 2-7 percent

Low = a seroprevalence of HBsAg is less than 2 percent

Below is a world map that identifies each of the categorized endemicity areas according to the 2006 Shepard study (Source: Mast et al. (28).).

(Picture Shepard 2006)

The Shepard study in 2006 stated, “Approximately 60 percent of the world’s population lives in the areas where HBV infection is highly endemic.” In the CDC Pink Book of 2012 the percentages had dropped to, “Approximately 45 percent of the global population live in areas with high prevalence of chronic HBV infection.” The CDC study also stated that the intermediate category was, “43% of global population,” and the low category was, “12% of global population.”

The causes for the prevalence of HBV within each category of endemicity is different, depending on the area of the globe they were located. Examples of this are, in the CDC Pink Book study, “In China, Southeast Asia, most of Africa, most Pacific Islands, parts of the Middle East, and the Amazon Basin, 8% to 15% of the population carry the virus.” “Most infections are acquired at birth or during early childhood, when the risk of developing chronic infections is greatest.” “In the United States, Western Europe, and Australia…infection occurs primarily during adulthood and only 0.1 to 0.5% of the population are chronic carriers” (CDC, 2012).

In the table below is a breakdown for the US population with HBV infections.

Prevalence of Hepatitis B in Various Population Groups

Population Group		Prevalence of Serologic Markers of HBV Infection
		HBsAg (%)	All Markers (%)
High-Risk	Immigrants/refugees from areas of high HBV endemicity.	13	70-85
	Clients in mental health institutions.	10-20	35-80
	Users of illicit parenteral drugs.	7	60-80
	Homosexually active men.	6	35-80
	Patients of hemodialysis units.	3-10	20-80
	Household contacts of HBV carriers.	3-6	30-60
Intermediate-Risk	Prisoners (male).	1-8	10-80
	Healthcare providers - frequent blood contact.	1-2	15-30
	Staff of mental health institutions.	1	10-25
	Heterosexuals with multiple partners.	0.5	5-20
Low-Risk	Healthcare providers - no or infrequent blood contact.	0.3	3-10
	Healthy adults (first-time volunteer blood donors).	0.3	3-5

           

During the time between the two studies, the immunizations for Hepatitis B Virus increased in the worldwide population. It is believed, this likely contributed to the decrease in prevalence of HBV worldwide. In areas where the vaccine is not as available, the prevalence appears to have been consistent with prior findings.

References

Center for Disease Control, The Pink Book: Course Textbook - 12th Edition Second Printing (May 2012), Hepatitis B: Epidemiology and Prevention of Vaccine-Preventable Diseases, On the Internet at http://www.cdc.gov/vaccines/pubs/pinkbook/hepb.htm (visited April 12, 2015).

 

Bureau of Labor Statistics, U.S. Department of Labor, Occupational Outlook Handbook, 2014-15 Edition, Epidemiologists, On the Internet at http://www.bls.gov/ooh/life-physical-and-social-science/epidemiologists.htm (visited April 12, 2015).

Shepard, Colin W., et al., Hepatitis B Virus Infection: Epidemiology and Vaccination, Epidemiologic Reviews, 2006;28:112-125, On the Internet at http://epirev.oxfordjournals.org/ (visited April 11, 2015)