Epidemiology

The lack of readily available serological tests means the worldwide prevalence of hepatitis D virus (HDV) infection is difficult to accurately ascertain. Studies suggest a wide range from 12 to 72 million people, with an estimated 10% to 15% of people with chronic hepatitis B virus (HBV) infection also having chronic HDV infection.[5] Around 5% of people infected with HBV (at least 12 million people) are estimated to also have HDV infection.[9][10] These patients are at high risk of developing liver cirrhosis and hepatocellular carcinoma within a few years.[10]

A systematic review and meta-analysis of HDV prevalence in the six World Health Organization (WHO) regions estimated a global prevalence of HDV infection of 4.5% (95% CI 3.6% to 5.7%) among people positive for hepatitis B surface antigen (HBsAg) and 0.16% (95% CI 0.11% to 0.25%) overall, representing 12 million HDV seropositive individuals globally (95% CI 8.7 to 18.7 million).[11] The geographical distribution of HDV infection does not mirror that of HBV infection, however, particularly the relatively low prevalence of HDV infection in many Asian countries. The highest prevalence of HDV infection is seen in parts of western and mid-Africa, Mongolia, eastern Europe, and parts of the Mediterranean.[11] HDV infection is uncommon in North America, northern Europe, and Japan, and confined to at-risk groups such as those with increased likelihood of sexual exposure, injection drug users, and immigrants from endemic areas.[1][12] Vaccination against HBV and immigration patterns have affected the prevalence of HDV infection.[11]

There are eight different genotypes of HDV, with genotype 1 being found mainly in North America, Europe, the Middle East, and north Africa; genotypes 2 and 4 in east Asia; genotype 3 in the Amazon Basin and South America; and genotypes 5, 6, 7, and 8 in west and central Africa.[3][12]

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