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WHAT IS HEPATITIS A?
There are several Hepatitis viruses (Hepatitis A, B, C, D and E) that cause human liver disease. Of the five virus types, only Hepatitis A can be transmitted by food through the fecal-oral route and is considered a major foodborne disease agent. Hepatitis E virus can be waterborne, and researchers have suggested that it could also be foodborne.1 Hepatitis B, C and D are not transmitted by food or water. The focus of this page is on Hepatitis A virus, and it is likely that most of the control strategies suggested here would also apply to Hepatitis E.
WHAT ARE THE SYMPTOMS?
Hepatitis A disease begins with mild symptoms, such as fever, headache, weakness, nausea and vomiting, after an average incubation period of four weeks. The infectious dose is presumed to be as low as 10 to 100 virus particles. The classic yellowing of the skin (jaundice) and dark-colored urine may appear at the onset of symptoms or later. Abdominal tenderness may occur, due to enlargement of the liver or spleen. The illness is usually more severe in adults than children. More than half of those children infected with Hepatitis A virus will show no symptoms, but infected individuals will shed the virus in their feces for a period of time.
Fatality is generally low, around 0.3%, but can be as high as 1.8% in those over 50 years of age. Blood tests are necessary to distinguish Hepatitis A infection from other hepatitis infections. Persons who may have been exposed to Hepatitis A virus may be treated with injections of immune globulin (antibodies). According to the CDC, such treatment is most effective if administered within two weeks of exposure.
HOW IS IT TRANSMITTED?
Transmission of Hepatitis A occurs primarily from direct or indirect fecal contamination. The virus particles are shed in the feces by infected individuals for several weeks at levels of up to 106 to 108 virus particles per gram, often before the onset of disease symptoms. The FDA states that water, salads and seafood are the most common vehicles. However, many outbreaks have been associated with ready-to-eat foods (foods that do not receive a substantial heat treatment prior to consumption). Contamination of foods can occur at any point in the production, harvesting, processing or preparation of foods if handled by infected workers or food handlers, although the preparation step is probably the most common phase in which food handler contamination occurs.
Oysters, clams, and other filter-feeding molluscan shellfish are a special case because they internalize and concentrate virus particles that might be present in sewage-polluted growing waters. Illness can occur from the consumption of raw or lightly cooked contaminated shellfish.
HOW IS IT CONTROLLED?
Hepatitis A virus cannot grow outside of the human host, thus time and temperature controls are not relevant. Control of Hepatitis A infection relies on prevention of contamination of the food through good sanitary practices, adequate personal hygiene and effective handwashing. Infected food workers must be excluded from handling food. Vaccines that provide immunity against hepatitis A are available. While the CDC suggests that vaccination protects against the spread of Hepatitis A virus, widespread vaccination of food handlers has not been recommended to-date, mostly because the disease is not common. Vaccination of handlers may be considered as a precautionary measure in areas that experience a Hepatitis A outbreak.
Control of shellfish-acquired Hepatitis A includes preventing harvest from contaminated growing waters. In molluscan shellfish, it has been demonstrated that ≥ 4 log10 reduction of the virus can be obtained by heating to an internal temperature of 185 to 194°F (85 to 90°C) for one minute.2 In the interest of being conservative, the United Kingdom standards recommend holding commercial shellfish at an internal temperature of 194°F (90°C) for one-and-a-half minutes to assure inactivation of the virus.3
Validated high-pressure processing may be useful for control of Hepatitis A in shellfish. A study in artificially contaminated oysters showed reductions of >1, >2 and >3 log10 of virus particles respectively with one-minute treatments at 350, 375 and 400 megapascals (MPa), within a temperature range of 8.7 to 10.3°C.4 A recent study shows that high-pressure processing may be more effective in inactivating Hepatitis A virus if applied at elevated temperatures (>86°F or 30°C).5
Hepatitis A is a reportable disease in the United States and other countries. A doctor treating an infected individual or a retail establishment manager who is aware of an infected worker must contact the local health department. Food handlers should inform their managers if they contract or are otherwise exposed to Hepatitis A.
REFERENCES AND FURTHER INFORMATION
1Yazaki Y, et. al. 2003.Sporadic acute or fulminant hepatitis E in Hokkaido, Japan, may be food-borne, as suggested by the presence of hepatitis E virus in pig liver as food. J Gen Virol. 84(Pt 9):2351-2357.
2Millard, J., Appleton, H., and Parry, J. V., 1987. Studies on heat inactivation of hepatitis A virus with special reference to shellfish. Epidemiol. Infection 98: 397-414.
3Lees, D., 2000. Viruses and bivalve shellfish. Int. J. Food Microbiol. 59: 81-116.
4Calci, K.R., et.al. 2005. High-Pressure Inactivation of Hepatitis A Virus within Oysters. Applied and Environmental Microbiology 71(1):339-343.
5Kingsley, D.H., et. al. 2006. Inactivation of Hepatitis A Virus by High-Pressure Processing: The Role of Temperature and Pressure Oscillation. J. Food Prot. 69(10):2454-2459.