“The Big 6” foodborne pathogens: Viruses

What you need to know about norovirus and hepatitis A, and how to prevent them.

Photo by Alex Munsell, Creative Commons
Photo by Alex Munsell, Creative Commons

Viruses differ from other foodborne pathogens because they are very small and need a living host to survive. For viruses to reproduce, they take over a healthy cell so instead of that cell creating more healthy cells, additional viruses are produced to infect other cells. Foodborne viruses originate in the human intestine, so contamination of food is a result of contact with sewage, contaminated water or poor personal hygiene by the person preparing the food (e.g. improperly washing hands after using the restroom or after coming in contact with an infected person’s feces or vomit). Foodborne viruses are the leading cause of gastroenteritis (infection of the stomach and intestines) and the two most common are norovirus and hepatitis A.

Norovirus is an acute gastrointestinal illness leading to inflammation of the stomach or intestines, sometimes both. According to the Centers for Disease Control and Prevention (CDC), norovirus is the leading cause of illness and outbreaks from contaminated food in the United States and causes 19-21 million illnesses, 56-71,000 hospitalizations and 570-800 deaths each year. Norovirus was previously known as Norwalk Virus and is sometimes referred to as ‘the cruise ship virus’ because of the increased likelihood of contact with the virus within a closed group on board cruise ships. Health officials also closely monitor illnesses on cruise ships, so the public is more likely to hear of a norovirus outbreak there than in other locations.

Hepatitis A is a liver disease that is the result of the hepatitis A virus. Hepatitis A can cause epidemics worldwide, leading to cyclical recurrences, that are more likely to affect developing countries due to contaminated drinking water and poor sanitation. The hepatitis A virus can range in severity from a mild illness lasting several weeks to a more severe illness lasting several months. Fortunately, there is a vaccine for hepatitis A available for those 12 months and older, anyone traveling to certain high-risk countries, or people at higher risk for infection. Once someone has hepatitis A, their body develops antibodies that prevent them from getting the virus again.

How do you catch it?

Norovirus and hepatitis A can both be contracted by ingesting small particles of feces through consumption of contaminated food or water. The majority of norovirus outbreaks occur in food service settings, caused by infected food workers touching raw, ready-to-eat foods with their bare hands. Norovirus is also able to live on surfaces contaminated with the virus and can be spread when an uninfected person touches that surface. Shellfish from contaminated waters can also be a source of norovirus. Norovirus spreads quickly in enclosed places with a lot of contact among groups of people like day care centers, schools, nursing homes and on cruises. In the United States, most norovirus outbreaks occur from November to April during cooler months when people are more likely to be indoors.

Hepatitis A can come from raw, ready-to-eat foods, raw or undercooked shellfish, contaminated drinking water and cooked foods not reheated after contact with an infected food handler. Symptoms of hepatitis A usually appear within two-to-six weeks and can develop over a period of several days. Additionally, people can spread the virus for up to two weeks without showing symptoms so it is possible to catch the virus from someone who is not yet aware that they are ill. This may be most true with children because the majority of them do not show symptoms.

Symptoms and Duration


  • Diarrhea, vomiting, nausea, stomach pain
  • Diarrhea is more common in adults and vomiting is more common in children
  • Incubation period lasts 12-48 hours
  • Usually lasts one-to-three days, though norovirus can last 4-6 days in high risk populations (older adults, young children and hospitalized individuals)

Hepatitis A

  • Jaundice, diarrhea, dark urine, fever, headache, nausea, abdominal pain, loss of appetite
  • Incubation period averages 28 days, ranging from 15-50 days
  • Duration varies from two weeks to six months in more severe cases
Who is most at risk?

People that work or spend large amounts of time in closed environments are most at risk for norovirus. This includes nursing homes, day care centers, schools and cruise ships. Norovirus can lead to dehydration from vomiting or diarrhea and young children, older adults, and those already sick with another infection are most at risk for severe symptoms. Norovirus is considered very common and the CDC estimates that most individuals will have norovirus about five times during their lifetime.

Most people in the United States are vaccinated against hepatitis A around 12 months of age but there are some groups that have a higher risk of infection worldwide. These include those who travel or live in countries where hepatitis A is common, family members or caregivers of a recent adoptee from a country where hepatitis A is common, those who live with someone who has hepatitis A, and those who have blood-clotting disorders like hemophilia. While most people infected with hepatitis A recover without complications, liver failure and sometimes death can occur. These more severe outcomes are rare among healthy individuals and are seen more commonly in those aged 50 and older and when combined with other liver diseases like hepatitis B or C.

How to prevent it


  • Wash hands thoroughly, especially after restroom use and before prepping food
  • Clean and disinfect surfaces contaminated by vomiting or diarrhea using a bleach-based cleaner (1000-5000ppm or 5-25 tablespoons bleach per gallon of water). Also clean and disinfect food contact surfaces.
  • Avoid food prep for others if vomiting or ill with diarrhea
  • Wash fruits and vegetables thoroughly before eating
  • Cook oysters and other shellfish to safe internal temperatures (145 degrees Fahrenheit) before eating
  • Wash clothing soiled by vomit or feces immediately to minimize spread of virus
  • Stay home for at least 48 hours after symptoms stop if working in a food service establishment to prevent spread of norovirus to others

Hepatitis A

  • Get vaccinated Hepatitis A is one of the few foodborne pathogens with an associated vaccine.
  • Wash hands thoroughly for 20 seconds with clean, soapy water after using the bathroom, changing a diaper, or before preparing food
  • Avoid raw shellfish, raw oysters, or other undercooked shellfish
    • Cook foods to safe internal temperatures. Boiling or cooking foods and liquids for at least 1 minute at 185 F will kill the virus

Check out previous articles in this series to learn more about the Big 6 Pathogens from Michigan State University Extension.

Other articles in this series

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