Hazard Identification

What is the hepatitis A virus?

The hepatitis A virus (HAV) is an enteric virus, which causes a liver disease in humans now known as hepatitis A (previously known by other names including infectious jaundice, viral hepatitis and infectious hepatitis). There are a number of different hepatitis viruses but only the HAV, and possibly the hepatitis E virus, can cause foodborne disease. HAV is a single stranded RNA virus belonging to the Picornavirdae family and the genus Hepatovirus.

Although HAV is most commonly spread by direct person-to-person contact via the faecal-oral route, there are many documented foodborne outbreaks in the literature. Foodborne outbreaks can often be traced back to an infected food handler or foods that have come into contact with faecally contaminated water.

Occurrence in foods

The HAV can only be present in foodstuffs as the result of faecal contamination. Although this means that any food that is handled under poor hygienic practices could potentially be contaminated with the pathogen, it is bivalve molluscan shellfish, such as oysters, cockles and mussels, which are most often considered to be a source of foodborne viruses. These shellfish concentrate any virus particles present in their tissues during filter feeding in faecally contaminated water. Depuration techniques used to decontaminate shellfish are more successful in reducing bacterial loading than affecting viral contamination.

In recent years fresh produce, such as salads, fresh fruits and vegetables, has increasingly been implicated in foodborne outbreaks of hepatitis A. These products are likely to be consumed raw or lightly cooked, and can become contaminated with faecal matter at almost any point during growing, harvesting, transport and packing.

Hazard characterisation

Effects on health

The infective dose for the HAV is unknown. However it is thought that as few as 10 - 100 virus particles could cause disease. The incubation time for symptoms to appear is on average about 4 weeks, but it can vary from 2 - 6 weeks. This long incubation time before the illness becomes evident can mean that it can be difficult to trace the exact source of the infection, and it can also mean that large numbers of individuals are affected before it is evident that there is viral contamination in the food chain.

Many cases of HAV infection are asymptomatic, particularly in children. When disease is evident, hepatitis A infection is usually a mild illness. Initial symptoms include headache, fatigue, fever, poor appetite, abdominal discomfort, nausea and vomiting. After a week or so, viraemia (where virus can be detected in the blood stream) and liver disease in the form of jaundice, or liver enzyme elevation, occurs. Hepatitis A is usually a self limiting disease lasting for up to 2 months, but in a small group of affected people, the HAV can cause long or recurring illness lasting up to 6 months. Infection can be fatal, particularly in people over 50 years old. In the USA, this age group has a mortality rate reported as 1.8 %

During infection individuals can excrete high numbers of virus particles (>10⁶ particles/g of faeces). The shedding of particles can start in the last 2 weeks of the incubation period and in some individuals can continue for up to 5 months after infection. Incidence and outbreaks

In many developing countries the disease is endemic and exposure during early childhood because of poor hygiene is common. Early childhood infections are usually asymptomatic and infer lifelong immunity.

Outbreaks of hepatitis A are more likely to occur in developed nations, or amongst travellers from developed countries to the developing world, because exposure to the virus during early childhood in individuals from developed regions is low. Countries where the adult population has no immunity are at risk of large hepatitis A outbreaks when food or water supplies are contaminated with the virus.

Contaminated water and bivalve shellfish such as oysters, cockles and mussels, are often associated with hepatitis A infections. The largest recorded foodborne outbreak of hepatitis A infections, involving 290,000 cases, was in Shanghai, China in 1988 and was caused by clams harvested from waters polluted by raw sewage.

Fresh fruits, such as strawberries and raspberries harvested by infected pickers, and associated products such as orange juice, have caused outbreaks in the UK and the USA, respectively. Imported lettuce and, more recently, imported raw/undercooked green onions have also caused large outbreaks in the USA.

Other foods linked to outbreaks include bakery products, sandwiches, iced beverages, milk and milk products, beer and soft drinks.

Sources

The human intestine is the main reservoir for the HAV and asymptomatic infected individuals, especially children, are an important source of the virus.

Transmission can occur by the faecal-oral route by direct person-to-person contact, or from the ingestion of faecally contaminated food or water. It has been reported that transmission of the virus can occur as the result of using contaminated drinking glasses. Infected food handlers with poor hygiene are a potential source of the virus in food. The virus could potentially be present in any water source or soil that is faecally contaminated.

Growth and survival characteristics

Viruses, including the HAV, are unable to multiply outside of the host. Although the HAV cannot grow in food or water, it can survive in many environments for some time. When excreted in human faeces the HAV can survive in the environment in water or soil for at least 12 weeks at 25°C. The HAV has a high resistance to many chemicals and solvents and it is more resistant to heat and drying than other enteroviruses. It can survive refrigeration and freezing for up to two years and it is resistant to acid (pH 1 for 2 hours at room temperature).

The HAV is resistant to low levels of free chlorine (0.5 - 1 mg free chlorine/l for 30 mins). It is also resistant to perchloroacetic acid (300 mg/l) and chloramines (1g/l) for 15 mins at 20°C. The virus can be inactivated on surfaces with a 1:100 solution of sodium hypochlorite, or household bleach in tap water.

Thermal inactivation

The HAV is relatively heat resistant, although thorough cooking at higher temperatures will usually inactivate the virus. It is resistant at 70°C for up to 10 mins but is inactivated at temperatures of 85°C for 1 minute. In the UK it has been recommended that cockles are heated to an internal temperature of 85 - 90°C for 1.5 minutes to inactivate HAV and data from the World Health Organization suggests that shellfish from HAV-contaminated areas should be heated to 90°C for 4 mins or steamed for 90 sec.

Control options

Strategies to reduce the risk of foodborne outbreaks of hepatitis A should focus on preventing foods from becoming contaminated. In developing countries young children should be kept away from areas where fresh produce is grown and harvested, and clean water should be used for the irrigation, washing and processing of foods. Shellfish harvesting areas should be monitored for sewage contamination.

Processing

Food handlers should implement frequent hand washing and the wearing of gloves particularly at points in the food chain where foodstuffs that will receive no further cooking are handled. In addition those suffering from symptoms of hepatitis A should be removed from the food production area until they have a medical release. In some parts of the USA food handlers are immunised against hepatitis A, but the effectiveness of such a policy is uncertain.

Product use

If food could be contaminated with the HAV, consumers should be advised only to eat thoroughly cooked foods from known sources and not to eat uncooked fruits or vegetables that they have not peeled or prepared themselves.

Legislation

There is no specific legislation in the EC or in the USA regarding levels of enteric viruses such as the HAV in foods.

Sources of Further Information

Published

Cook, N., Rzezutka, A.
Hepatitis viruses in "Emerging foodborne pathogens".
Eds Motarjemi, Y. & Adams, M. Cambridge. Woodhead Publishing Ltd, 2006, 282 - 308.

Fiore, A.E.
Hepatitis A transmitted by food.
Clinical Infectious Diseases, 2004. 38, 705 - 715.

Koopmans, M. & Duizer, E.
Foodborne viruses: an emerging problem.
International Journal of Food Microbiology, 2004. 90, 23 - 41.

Koopmans, M., von Bonsdorff, C-H., Vinjé, J., de Medici, D. and Monroe, S.
Foodborne viruses.
FEMS Microbiology reviews, 2002. 26, 187 - 205.

On the web

Hepatitis A. World Health Organization (2000).
http://www.who.int/csr/disease/hepatitis/HepatitisA_whocdscsredc2000_7.pdf