Hepatitis A

Global Epidemiology

This map is reproduced with acknowledgement to WHO. Note that the data shows prevalence NOT incidence. Countries that are not coloured have not reported cases to WHO, which does not necessarily mean that no cases are occurring.

Hepatitis A occurs worldwide; it is estimated to cause around 1.5 million cases of clinical hepatitis per year. The incidence of hepatitis A is closely related to socio-economic conditions, and sero-epidemiological studies show that prevalence of anti-hepatitis A antibodies in the general population varies from 15% to close to 100% in different parts of the world [1]. It is endemic in many resource-poor countries where food and water hygiene may be of a low standard.

Countries where hepatitis A is highly endemic include the Indian Sub-Continent (particularly India, Pakistan, Bangladesh and Nepal), the Far East (not Japan), North Africa, South and Central America, Sub-Saharan Africa and the Middle East. Clinical cases of hepatitis A in adults are rare in these countries, as most will have been exposed to the virus at a young age and will have subsequently acquired life-long immunity. Most of the resource-rich countries such as those in Western and Northern Europe, Australia and New Zealand, North America and Japan are of low endemicity for hepatitis A, although small outbreaks occur from time to time. Most of the population in these countries will have no immunity to hepatitis A and are therefore susceptible to infection as adults and children should they be exposed to the virus.

In some countries in Eastern Europe and in parts of Asia and America, there has been a recent reduction in endemicity from high towards low, such that hepatitis A is more common in young adults and teenagers who may not have had previous exposure (and therefore not acquired any immunity) to the virus as a child. Conversely, hepatitis A is rare in older adults as most of them will most likely to have been exposed to the virus as a child and therefore will have acquired immunity.

References

1. World Health Organization. Hepatitis A vaccines: WHO position paper. Weekly Epidemiological Record 2000 4 Feb; 5: 38-44. Available online at http://www.who.int/wer/pdf/2000/wer7505.pd