7 Hepatitis A

7.3 Epidemiology

7.3.1 Global burden of disease

In developing countries the disease is virtually confined to early childhood and is not an important cause of morbidity. Almost all adults in these countries are immune. In developed countries the infection is less common in childhood and only 20–40 percent of adults are immune.

Viral spread occurs readily in households, in early childhood services and in residential facilities that care for the chronically ill, disabled or those with a weakened immune system. In early childhood services, typically the adult guardian develops symptomatic disease while the primary source, the infected young child, is asymptomatic. The risk of spread in early childhood centres is proportional to the number of children aged under 2 years wearing nappies. Infection in these early childhood services is an important source of outbreaks for whole communities.

Other groups at the highest risk of contracting the disease include people in close contact with an infected person, and travellers to areas with high or intermediate rates of hepatitis A infection. These continents and countries include the Pacific, Africa, Asia (except Japan), Eastern Europe, the Middle East, South and Central America, Mexico and Greenland. Others also at greater risk of contracting HAV are people who have oral–anal sexual contact, illegal drug users, those with chronic liver disease or blood-clotting disorders (or who receive clotting factor concentrates), food handlers, and laboratory workers who handle the virus.

Universal and targeted programmes for childhood immunisation have been introduced in several countries, including Israel, the US and Australia. Acute HAV infection has almost been eradicated in areas with HAV immunisation programmes.

7.3.2 New Zealand epidemiologyTop

The rate of HAV in New Zealand has declined from 145.7 per 100,000 in 1971 to 1.8 per 100,000 in 2012.1 This fall in rate is attributable to the use of HAV vaccination in travellers and a reduction in HAV prevalence overseas. In 2013, 91 cases were notified compared to 82 in 2012. From 2000 to 2013, between 22 and 43 percent of notified cases required hospitalisation.

Age was recorded for all cases in 2012, with the highest rates occurring in the 5–9 years age group (21 cases, 7.2 per 100,000 population), followed by the 1–4 years age group (13 cases, 5.2 per 100,000) and the 10–14 years age group (10 cases, 3.5 per 100,000). Ethnicity was recorded for 80 (97.6 percent) cases. The Middle Eastern/Latin American/African ethnic group had the highest notification rate (5 cases, 13.2 per 100,000), followed by the Asian ethnic group (53 cases, 13.0 per 100,000). One person-to-person outbreak occurred in 2012, involving 30 cases.1

Of the 76 cases with travel information recorded, 38 (50 percent) had travelled overseas during the incubation period of the disease. The countries most frequently visited included India (14 cases), Fiji (5 cases), Samoa (5 cases), Pakistan and Singapore (3 cases each).1

Hepatitis A outbreaks continue to occur, the most recent in Ashburton in 2013. Transmission was through person-to-person spread in homes and early childhood centres. A mass vaccination of preschool children was implemented to curb the spread.

Figure 7.1 illustrates the overall national downward trend since a peak of notifications in 1997. There have been no deaths with hepatitis A as the primary cause since 2002.

Figure 7.1: Hepatitis A notifications, by year, 1997–2013

Figure 7.1: Hepatitis A notifications, by year, 1997–2013

Source: Institute of Environmental Science and Research