Global Epidemiology of Hepatitis B Virus (HBV) Infection

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10 Jan 2011 Vol 4 No.1 North American Journal of Medicine and ScienceNorth America (United States and Canada). In the UnitedStates, the National Health and Nutrition Examination Study(NHANES) found the age-adjusted prevalence of past andpresent infection to be 4.8% from data collected between1996 and 2006. The prevalence of active chronic HBVinfection was 0.3%, or about 730,000 total infected persons. 21Before hepatitis B vaccines were licensed in 1982, anestimated 200,000-300,000 persons became infected withHBV in the United States each year, with rates of infectionpeaking in the mid-1980s. 22 However, since the initiation ofincreased vaccine coverage in 1991 targeting prenatalscreening of infected pregnant women and universalvaccination of infants, adolescents and adults at risk forHBV, the incidence has declined. The Centers for DiseaseControl and Prevention (CDC) estimated that there were13,000 acute clinical cases and 43,000 newly infectedpatients in the year 2007, which is significantly less than prevaccinationprevalence rates. 23 The incidence of HBV variesgreatly, with the highest rate in immigrants or refugees fromareas of high endemicity, followed by the Native Alaskansand blacks. Among whites, Hispanics have a higher rate ofinfection than non-Hispanics. The incidence and prevalencerates are generally higher in urban settings and among adults,particularly males, ages 25-44 years. 24In Canada, the prevalence of hepatitis B varies greatlydepending on the population. The overall prevalence in thegeneral population is low, about 0.5-1.0%; however,assessments based on distinct populations can range from aslow as 0.1% in people born in Canada to 6.9% in the Inuitpopulation and 7.4% in immigrants from highly endemiccountries. 25 In 1999, the incidence of acute HBV infectionwas estimated to be 2.3/100,000 population, approximately700 cases per year. 26 The rate is higher among males thanfemales and peaks at the age of 30 to 39 years. 27 As in theUnited States, adult horizontal transmission is the mostcommon route of transmission, except for recent immigrants,native Alaskans and native northern Canadians, wherevertical and childhood horizontal transmissions are morecommon. 28Mexico, Central America and South America. Hepatitis B isconsidered to be highly prevalent in this region, but there isvariability among and within each country. The estimatedprevalence ranges from 0.5-8.0%, with the total number ofcarriers approaching 11 million. 29,30 Mexico and most ofCentral America have low-intermediate endemicity rangingfrom 1.0-2.0%, except for Honduras, the DominicanRepublic and Haiti where there is a higher prevalence of 3-4%. In South America, the rate of HBsAg carriage is as highas 8% in the native population of the Western Amazon Basin(Brazil, Colombia, Peru and Venezuela). With increasingdistance from this area, the HBsAg prevalence decreases withChile, Uruguay, Paraguay and Argentina having the lowestHBsAg prevalence ranging from 0.5-1.0%. 31Routes of transmission are highly variable in Latin America.The highest prevalence has been reported to be among 20 to40 year olds and the lowest prevalence in children youngerthan 12 years, supporting adult horizontal transmission as themost common route of infection in this area. In addition tothe expected means of adult transmission by sexual orparenteral practices, there are significant rates of infectionthrough cultural practices such as tattooing. However,vertical transmission and childhood horizontal transmissionare still important in areas of high endemicity such as theAmazon Basin. 31HBV in EuropeThe prevalence of HBV is heterogeneous in this region with28, 32rates ranging from < 0.1% to as high as 12%. Europe canbe divided into three types of epidemiological patterns. Thefirst pattern occurs in Northern Europe (Scandinaviancountries and the United Kingdom) and is generallycharacterized by a low HBsAg carrier rate of < 0.1%. Thesecond pattern exists in most Western European countries,where the carrier rate ranges between 0.1% and 0.5%. Thefinal pattern can be found in Southern Europe (countriesbordering the Mediterranean Sea) and Eastern Europe where33, 34the carrier rates in some parts can be greater than 8%.Overall, the highest incidence of HBV in Europe is in the 25to 44-year old age group, followed by the 15 to 24 year-oldage group. The infection is more common in males (1.33cases per 100,000) than females (0.58 cases per 100,000). 35The European countries follow the general rules oftransmission. In countries with intermediate to highendemicity, vertical and childhood horizontal transmissionwithin infected households are the most common routes ofinfection, whereas in low endemic areas, intravenous druguse and sexual activity are the predominant means. Forexample, in the Netherlands where the prevalence rate is low,sexual transmission is the most frequent mode of infection. 36In Central and Eastern Europe, where the prevalence rates arehigher, vertical and childhood horizontal transmissioncontribute to the high endemism in the former USSR. 37Additionally, after the introduction of dry heat sterilization inthe 1970s which was insufficient to eliminate HBV, multiplestudies in Poland showed that nosocomial infections fromblood transfusions and medical procedures accounted for upto 60% of HBV infections in adults and 80% in children. 34Today, strict blood screening, vaccination and improvedsanitation practices have led to a declining trend of HBVprevalence in most countries.HBV in the Eastern MediterraneanThe WHO Eastern Mediterranean region extends from thecountries of North Africa through the Middle East toPakistan. The WHO estimates that the HBsAg prevalence inthis region ranges from 1-10%, making it a region ofintermediate to high endemicity. 28 A study of villagepopulations in Egypt, published in 1985, revealed an overallHBV prevalence rate of 11.7% and a higher prevalence rateof 20.8% in young adults between the ages of 14-18 years.In these populations, antibodies to hepatitis B core antigen(anti-HBc) were found in nearly 90% of both men and
North American Journal of Medicine and Science Jan 2010 Vol 4 No.1 11women. 38 More recent studies, published in 2009 and 2010,show that prevalence rates have decreased in Egypt. A studyof 616 barbers and their clients in a mixed urban and ruralsetting revealed a HBsAg prevalence rate of 4.2%. 39 Anotherstudy screened almost 56,000 asymptomatic blood donors,mostly from rural areas, and found the seroprevalence rate tobe only 1.3%. 40In a 2002 Pakistani study, the prevalence of HBV infectionwas found to be 3.3% from a sample of over 100,000voluntary blood donors. 41 In 2005, a study in the obstetricand gynecological population in Pakistan found a 4.6%prevalence in women of childbearing age. 42 A recentpopulation-based study in Iran showed a prevalence rate ofhepatitis B surface antigen to be 2.6% in 6,583 randomlysubjected subjects from three provinces in Iran, namelyTehran, Golestan, and Hormozgan. 43Throughout the Eastern Mediterranean region, transmissionoccurs through childhood horizontal and adult horizontalroutes, and less commonly, vertical routes. Risk factorsassociated with infection include residence in a rural area,overcrowding, poor sanitary conditions, parenteral drug use,exposure to blood products, medical procedures, ear piercingand scarification. 38HBV in AfricaThis region covers all of Sub-Saharan Africa and Algeria.Africa has the second largest number of chronic carriers afterAsia and is considered a region of high endemicity. Theexact burden of hepatitis B in Africa is difficult to assess dueto inaccurate records and under-reporting, but between 70and 95% of the adult population show evidence of pastexposure to HBV infection and the estimated HBsAgseroprevalence ranges from 6-20%. 44,45Western Africa has the highest rates of endemicity withinAfrica with as many as 95% of the adult populationdisplaying markers of past HBV exposure. The prevalencerate in Gambia and Senegal are about 15%, with age-specificprevalence as high as 20% in 10- to 20-year olds. Notsurprisingly, this region also has one of the world’s highestrates of HCC. In Gambia, HCC is the most common canceramong men and the second most common cancer amongwomen. 6,46,47Different areas of Africa have varying prevalence rates.Some of the variability lies in the size of the study and thegeographical location in Africa, but it appears that in general,higher prevalence rates are encountered in rural areascompared to urban areas. A study of chronic HBV infectionamong 2364 urban black children in Soweto, Johannesberg,South Africa showed an HBsAg positivity of 1%. This lowcarrier rate applied equally to children from the lowest andthe highest socioeconomic groups in Soweto. This is incontrast to the established prevalence rate of 15% in ruralblack children in southern Africa. This significant differencein HBV carrier rate could be attributed to poor hygiene andgreater chances of HBV transmission through skin abrasions,insect bites, use of contaminated needles, tribal scarificationand ear piercing using contaminated equipment. 48,49In contrast to Asia where perinatal transmission is mostcommon, horizontal transmission in childhood is thought tobe the predominant mode of infection in Africa. Forexample, in Western Africa, HBV infection is uncommon innewborns, but then infection rates rise with age. By the ageof 2 years, 30% of West African children have been infectedwith HBV and 15% have developed persistent infection. Bythe age of 10 years, 90% of children have become infectedand 20% have become chronic carriers. A major reason forthe relatively low rate of perinatal transmission is the lowerprevalence of HBeAg positivity, which is considered amarker of active viral replication. A lower prevalence ofHBeAg positivity has been observed in mothers from Sub-Saharan Africa compared with mothers in Asia, suggesting alower potential for vertical transmission. 45HBV in South-East AsiaThis region is comprised of Bangladesh, Bhutan, NorthKorea, India, Indonesia, Maldives, Myanmar, Nepal, SriLanka, Thailand and Timor-Leste. It is considered to be ofintermediate to high endemicity with prevalence ratesranging from 1-10%. 28In India, the national prevalence rate has been estimated to be4% with approximately 36 million carriers overall. 50 Anextensive review by the Indian National Association for theStudy of Liver Diseases estimated the average nationalprevalence rate to be 4.7%. 51 However, as with othercountries that cover a large geographic area, the prevalenceof hepatitis B is variable throughout the country with agradient of generally increasing prevalence from north tosouth. The lowest prevalence is 2.3% in a large cohort of20,000 blood donors in northern India. 52 The highestreported rate is 5.7% in a community based study in almost2000 people from southern India. 53 Transmission is mostlythrough childhood horizontal spread due to sub-optimalhygiene and crowded living conditions.The impact of universal vaccination can clearly be observedin Thailand. Prior to universal vaccination, there was aprevalence rate of 8.2% in blood donors in Thailand. 54 In2004, twelve years after the initiation of universalvaccination, the prevalence of HBsAg carriers decreased to4% among the 6213 subjects studied. 55 This trend was alsowitnessed in a hepatitis B screening program of healthy Thaiworkers going abroad. In 1996, the annual prevalence inalmost 25,000 workers was 6.1%; by 2001, the prevalencehad decreased to 2.8%. 56HBV in the Western PacificThe Western Pacific region includes: Australia, BruneiDarussalam, Cambodia, China, Cook Islands, Fiji, Japan,
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