Estimating the global prevalence of hepatitis B.

The substantial global burden of hepatitis B virus (HBV) infection is increasingly recognised. Recent estimates suggest that HBV infection caused 686 000 deaths in 2013, placing HBV in the top 20 causes of human mortality. Despite this, comprehensive reviews of data regarding the burden of chronic HBV at regional and national levels have been scarce. This is an area of particular importance in view of the global diversity in chronic HBV prevalence, and the disproportionate burden experienced by people living in low-resource settings. In The Lancet, Aparna Schweitzer and colleagues report the most robust estimates to date of the prevalence of chronic HBV by country and region. Their findings highlight both the substantial global burden of chronic HBV, and the concentration of the epidemic in specific countries. This systematic review collated data from HBsAg seroprevalence studies including 109 415 627 individuals, across 161 countries, published between 1965 and 2013. Overall the authors estimate that 3·61% (95% CI 3·61–3·61) of the global population is living with chronic HBV infection. Prevalence by country varied from as low as 0·01%, in Norway and the UK, to greater than 20% in countries such as South Sudan (22·38%, 20·10–24·83) and Kiribati (22·70%, 20·19–25·41), building on previous work that has shown the diversity in prevalence according to region. These results highlight both the successes achieved, and the continuing challenges experienced, in the global response to HBV. Previous assessments indicate that there has been a clear decrease in prevalence of chronic HBV in many areas, including some countries in the South East Asian, Eastern Mediterranean, and Western Pacific WHO regions. This decrease applies mostly to countries where routine infant immunisation programmes were implemented and have achieved high coverage. The study by Schweitzer and colleagues also suggests a decrease in HBV prevalence at the global level in many countries between the two time periods 1957–1989 and 1990–2013. However, the burden of disease persists in many low-income and middleincome countries, and in some countries the prevalence of HBV is increasing. The number of affected individuals was highest in the Western Pacific (95·3 million, prevalence estimate 5·26%, 95% CI 5·26–5·26) and African (75·6 million, prevalence estimate 8·83%, 8·82–8·83) regions, which together included nearly 70% of the global burden. The findings should also be considered in the context of global evidence regarding adverse outcomes from chronic HBV, specifically liver cancer, which is now the third leading cause of cancer deaths, and which disproportionately affects developing countries. Schweitzer and colleagues excluded studies specific to population groups at particular risk of chronic HBV infection, such as migrants from endemic areas resident in low-prevalence countries. Since in some countries these groups form a substantial part of the population and represent the majority of those living with chronic HBV infection, this exclusion leads to an underestimate of the total burden of HBV. For example, the number of people living with chronic HBV in the USA was estimated as 843 724 (estimated prevalence 0·27% [95% CI 0·24–0·30]); however a recent meta-analysis suggested that 1·7 million people, of whom 1·3 million were migrants, were living with chronic HBV in the USA, an estimate double that of the present study. The increasing prevalence of chronic HBV infection in these populations is contributing to the rising incidence of liver cancer, which is now the fastest increasing cause of cancer deaths in the USA. Unavoidable limitations in this type of study include sparse or absent seroprevalence data in some countries. Improvement of the range and quality of HBV prevalence data is important, as is accurate and