Public Health officials are tracking multiple reports of norovirus-like illness (nausea, vomiting, and diarrhea) after eating raw oysters. Since January, Public Health – Seattle & King County has received multiple reports involving as many as 39 people whose illnesses we believe came from eating raw oysters. We talked with Dr. Meagan Kay, Medical Epidemiologist with Public Health, to better understand the risks of norovirus associated with oysters and how to prevent illness.
Let’s start with the basics. What is norovirus?
Norovirus is a very common, highly contagious virus that causes diarrhea, vomiting, nausea, stomach pain and can also cause body aches, fever, and headache. While most people recover after 1-3 days of these symptoms, the repeated bouts of throwing up can cause dehydration, particularly in children, older people, and people with underlying illnesses.
How do you know this was norovirus that made people sick?
We do not have laboratory confirmation for any of the cases, but signs and symptoms are suggestive of norovirus. Often in norovirus outbreaks no laboratory testing is done. As many as 39 people may have become ill, though not all were interviewed directly by Public Health. Read more on the illnesses reported to Public Health here.
Where are the oysters coming from that have made people sick?
Oysters linked to the illnesses reported in King County appear to come from different bays and beds across the state, including northern and southern regions of Puget Sound. The Washington State Department of Health has closed a section of Samish Bay to all shellfish harvest because of reports of norovirus.
What can be done to reduce my risk from eating oysters?
Oysters have long been recognized as a source of norovirus. Raw or undercooked oysters seem to be a particular problem. Protect yourself and reduce your risk by choosing fully cooked oysters that have been thoroughly fried, baked, or made into a stew that has reached 145°F. Use a thermometer to check. Quick steaming or cooking until the shells just open may not be enough to protect against norovirus illness. Norovirus can survive cooking temperatures up to 140°F so cooking to 145°F provides a margin for safety. Avoid raw oysters like oyster shooters and oysters on the half shell. Adding hot sauce or lemon to oysters does not kill the virus.
What other steps can be taken to reduce my risk from norovirus?
Wash hands, cutting boards, and counters used for shellfish preparation immediately after use to avoid cross contaminating other foods. And, as general advice to prevent the spread of norovirus, wash hands thoroughly with soap after using the bathroom or changing diapers, and before preparing any food or eating. Wait at least 48 hours after the last episode of vomiting and/or diarrhea before preparing any food for others.
Are consumers warned of the risk of eating uncooked oysters?
When eating out, pay attention to any consumer advisories on the menu. The advisory is there to let you know which animal foods are served raw or undercooked. There is an increased risk of becoming ill from consuming any raw or undercooked meat or seafood. Read Public Health’s factsheet on norovirus for more information on norovirus infection.
Why are oysters a particular risk?
Shellfish such as oysters, clams, and mussels are filter feeders. They ingest norovirus if it is present in the water. Because they are filter feeders, these shellfish may concentrate the virus to much higher levels than might be found in the surrounding water. Though all shellfish can be a source of norovirus infection if consumed raw or undercooked, oysters are much more commonly consumed raw than other shellfish; we are not aware of any norovirus cases linked to consumption of other types of shellfish right now.
What does Public Health do when someone reports illness from oysters or other shellfish?
Public Health investigates every report of illness after consumption of shellfish whether we believe the illness to be norovirus, vibrio, or some other pathogen. Inspectors visit the food establishment where the person obtained the oysters. Shellfish tags are collected to determine the source of the oysters, and oyster handling procedures are reviewed with food establishment staff. We provide the shellfish tag information to the Washington state Department of Health Shellfish Program.
Our inspectors also evaluate other risk factors that may contribute to the spread of norovirus such as the presence of any ill food workers, ill family members, poor handwashing practices, or touching ready-to-eat foods with bare hands. If any risk factors are identified, we make sure the establishment manager takes appropriate interventions to prevent further spread of norovirus. In this current outbreak, most of the food establishments where people purchased oysters and then got sick did not have any other risk factors, with limited exceptions. Read the outbreak report on this outbreak.
What is the Washington state Department of Health (DOH) Shellfish program’s role in reducing disease risks from shellfish?
DOH regularly tests water quality in shellfish growing areas and checks shorelines and surrounding areas for pollution sources. They also monitor shellfish for biotoxins, pathogens, and other contaminants. DOH also assures that commercial shellfish operations follow strict sanitation standards. And DOH closes shellfish areas when spills or other pollution impacts water quality, and closes harvest areas and conducts recalls when they identify shellfish as the source of contamination. Learn more about the DOH Shellfish program on their website.
Am I at risk for norovirus if I harvest my own oysters (or clams or mussels?)
Before harvesting shellfish yourself (as opposed to buying it a commercial establishment) always check DOH’s shellfish safety page for updated information about which areas are closed to recreational harvest.
How exactly does norovirus spread?
Norovirus is highly contagious, so it’s easy to spread to when you have close contact with an infected person such as sharing utensils or taking care of someone who is sick with norovirus, touching surfaces and objects that have been contaminated with norovirus, or, as in the case of this oyster related outbreak, eating foods that have been contaminated with the virus.
What should I do if I or someone I live with gets norovirus?
If a person gets norovirus from eating a contaminated oyster (or from any other source) it is possible to spread the virus to people who didn’t eat any oysters. Norovirus is highly contagious, and infected people are mostly likely to spread it from the moment they feel ill until at least three days after they no longer have symptoms. It’s very important that people who are sick with norovirus stay home for 2-3 days after symptoms have ended to keep from infecting other people. In addition:
- Wash your hands carefully with soap and warm water frequently, particularly after using the bathroom, changing diapers, before eating, and before preparing food.
- Wash fruits and vegetables thoroughly before eating them, and avoid undercooked foods.
- If someone gets sick put on gloves and promptly clean toilets, sinks, and other areas that may be contaminated with vomit or stool, including removing and washing clothing and linens. After cleaning, disinfect with a solution of 1/3 cup household bleach mixed with one gallon of water.
- Remove and wash clothing or linens with hot water and detergent immediately if they become contaminated.
- Avoid preparing food for others for at least two to three days after symptoms have ended.
For more information visit:
Washington state Department of Health Shellfish program
Public Health website on norovirus.
Originally posted on March 28, 2017.