Foodborne Hepatitis A Outbreaks: The Basics
Hepatitis A is caused by the hepatitis A virus. Hepatitis is transmitted either by contact with the feces of an infected person or consumption of food that has been contaminated by the feces of an infected person. The incubation period is between 15 and 50 days, making it difficult for health officials to pin point the source of a hepatitis A infection. The result is that there are very few CDC-confirmed hepatitis A outbreaks in the United States each year.
Once someone gets hepatitis A, a permanent immunity to the virus is developed. It is estimated that about one third of the U.S. population has been infected with hepatitis A virus. Hepatitis A initially manifests itself as a fever, nausea, vomiting, diarrhea, muscle pain and malaise. Later symptoms can include jaundice, dark-colored urine, light colored stools and enlargement of the liver and/or spleen. Generally, hepatitis A lasts a few weeks. For about 10% of those infected, the symptoms are recurring for up to 6 months. In a small percentage of cases of hepatitis A, liver failure can occur, which can lead to severe illness of death. Approximately 25,000 cases of hepatitis A are reported to the CDC each year. However, with adjustments made for underreporting and asymptomatic hepatitis A (usually with children less than 5 years of age) the number of hepatitis A cases is estimated to be over 260,000 per year
It is unknown how many hepatitis A cases are caused by consumption of contaminated food for the following reasons:
HAV contamination of a food product can occur at any point
during cultivation, harvesting, processing, distribution, or preparation.
Recognizing foodborne transmission using routine surveillance
data may be difficult because (1) case patients may
have difficulty recalling food histories during the 2-6 weeks
before illness, (2) cases may accrue gradually or not be reported,
(3) a food item may be focally contaminated, (4) some exposed
persons have unrecognized HAV infection, (5) some exposed
persons have preexisting immunity (from a previous infection
or previous vaccination), (6) persons who acquire infection
through contaminated food are not recognized amid an ongoing
high incidence in the community, and (7) cases are geographically
scattered over several public health jurisdictions.(Fiore)
Most foodborne hepatitis A outbreaks are linked to food handlers who are infected with the hepatitis A virus. Just one food handler with hepatitis A could potentially infect hundreds of people. For this reason, health departments investigate food handlers who are found to have hepatitis A and take measures to prevent a hepatitis A outbreak. The CDC recommends that post-exposure prophylaxis be considered for persons who consume food prepared by an infected food handle. This inoculation is highly effective if given within 2 weeks of exposure.
The other major source of foodborne hepatitis A outbreaks is fresh produce that was contaminated with the hepatitis A virus during cultivation, harvesting, processing or distribution. Green onions and frozen strawberries, both of which require extensive handling prior to distribution, have been the cause of several hepatitis A outbreaks. Again, one person infected with hepatitis A could potentially contaminate enough produce to make hundreds of people sick.
References
Fiore, AE. Hepatitis A Transmitted by Food. Clinical Infectious Diseases, 2004 ;38:705-15.
