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When you think of food poisoning, you probably think of bacteria like E. coli, salmonella, or staphylococcus. Foodborne illness can also be caused by other pathogens, including viruses and parasites. If I were to ask the average person what the leading cause of food poisoning is, they’d likely say something like salmonella. But what is the leading cause?
Well, salmonella is definitely a leader. However, it is a virus that is the heavy-weight champ. In fact, according to the CDC, viruses are responsible for at least 67% of foodborne illnesses of known etiology, annually.
Of the top five pathogens likely to be responsible for a case of food poisoning, norovirus is number one. In 2011, the CDC estimated there were 5,461,731 cases of norovirus food poisoning. Salmonella was number two, at an estimated 1,027,561 cases.
Not only is norovirus the leading cause of foodborne illness, the CDC also believes it to be responsible for half of all food poisoning cases.
Since the symptoms of norovirus will usually be seen by individuals as the “stomach flu” or a “bad stomach bug” most cases probably go unreported and the actual number of outbreaks is probably much higher.
The same could be said, of course, of other causes of food poisoning. When everybody at work comes down with the stomach flu, chances are high it is a norovirus.
This is not just one virus. Noroviruses, instead, are an entire genus of similar viruses, called Norovirus, in the family Caliciviridae. These viruses were previously called Norwalk-like viruses or NLV.
How do you get Norovirus?
Norovirus is usually acquired from restaurants, where workers transmit the virus to raw food or previously cooked food when they touch it with bare, unwashed hands. It is highly contagious and can be passed from person to person through contact, sharing food, and sharing utensils. You can also be infected by touching a surface contaminated with norovirus. See the CDC overview for more information.
It can take as few as 10 viruses to make a person ill, while persons infected can shed up to 10,000,000 viruses per gram of feces during the height of the infection. In other words, even the tiniest bit of contamination can cause another person to become ill.
Since there are many different kinds, you can get it multiple times throughout your life. Acquired immunity to one will not protect you from another type.
Although most outbreaks occur when persons whose skin is contaminated with norovirus touch food in food service operations, outbreaks sometimes occur from foods that are contaminated at their source and are eaten raw, such as oysters, fruits, and vegetables.
Oysters and other filter-feeding shellfish are particular causes of norovirus infection because they often live in environments that are contaminated with human sewage, and then are eaten raw or only lightly cooked.
Although mussels are usually cooked, they are usually only cooked until their shells open, which means that the internal temperatures reached may not be sufficient to kill the virus. It is important to not gather shellfish from just any area.
What are the Symptoms of Norovirus?
Norovirus inflames the stomach and/or the intestines and causes severe acute gastroenteritis. The symptoms are, in order of prevalence, are:
- diarrhea
- throwing up
- nausea
- stomach pain
- fever
- headache
- body aches
It can take 12 to 48 hours after being exposed to the virus to develop symptoms.
Like other food poisoning, you cannot assume the cause was the last food you ate before becoming sick, or the last person with whom you came in contact.
Once you get ill, you will be very ill! The symptoms will usually pass within two to three days, but as cases of food poisoning go, norovirus is a miserable experience. People vomit up to twenty times a day, if not more.
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Prevention and Household Disinfection
Follow the CDC advice for the prevention of norovirus.
As for cooking, norovirus is relatively heat resistant and can survive temperatures of up to 140° F. If you view safe temperatures for foods, you will see that a safe holding temperature for food is not necessarily enough to kill the virus so when cooked food is handled by persons with the virus, who have not properly washed their hand and/or are not wearing gloves, cooked food can become contaminated and then make you sick even if the food is being kept warm.
It is important to know that norovirus can appear in a person’s stool before they actually become ill, and it can linger in the stool for up to three weeks after symptoms subside. Household surfaces can become contaminated and it can be difficult to rid them of the virus. This is why, if you become ill, it is important to wash your hands thoroughly with soap and warm water for at least 20 seconds after using the bathroom.
If there are young children in the house, their toys could become contaminated. Young children are at much higher risk of serious illness, so if the household becomes sick with what you suspect to be a norovirus (or any other food-poisoning incident), make sure they follow proper hygiene and wash or wipe down toys and other surfaces with disinfecting solutions.
Alcohol-based hand sanitizers are not a substitute for frequent hand washing, but they may help when used in between washings.
The leading disinfectant wipes, Lysol®, and Chlorox® wipes do not kill norovirus.
Lysol disinfecting spray, according to its label, does kill the virus. The Environmental Protection Agency maintains a list of germicidal cleaners or disinfectants approved for norovirus disinfection. Lysol disinfectant spray is not on the list. The EPA-approved list can be accessed here (requires Adobe Reader to view pdf).
Alternatively, a solution of household bleach and water can be used. However, the amount of bleach to use is uncertain and may differ with different types of surfaces. Concentrations of 1000-5000 ppm may be used, which corresponds to 5 to 25 tablespoons of household bleach per gallon of water.
Surfaces must first be cleaned with water and detergent and then a bleach solution must be applied and allowed to sit for up to five minutes. Food contact areas and food utensils must be rinsed off after bleach is applied.
Metrex CaviCide1 is one of many disinfectant solutions on the EPA list and can be used to kill norovirus and has wide activity against viruses, bacteria, and fungi with one-minute kill times. Cavicide can be used as an everyday cleanser, but understand that when fecal matter or vomit gets on surfaces, i.e. gross contamination, they need to be thoroughly cleaned prior to disinfection.
Follow label directions exactly when using any disinfectant solution. Kill times can be different for different types of pathogens. Cavicide wipes are also available, but these do not list norovirus among the kill claims, and the wipes are not listed by EPA.
Relative Danger of Norovirus
Norovirus certainly affects more people than salmonella and other infections such as clostridium, campylobacter, or staphylococcus. However, it is not the most dangerous food-borne illness.
In 2011, salmonella resulted in an estimated 19,336 hospitalizations while norovirus resulted in 14,663 hospitalizations. While these numbers may seem close together, the percentage of norovirus cases requiring hospitalization was much lower, only around 0.26 percent, while 1.9% of salmonella cases resulted in hospitalization.
Norovirus also resulted in fewer deaths than salmonella, 149 compared to 378. Toxoplasmosis caused 327 deaths, and listeria caused 255.
The biggest danger of norovirus in otherwise healthy individuals is dehydration. The most important home treatment is drinking plenty of fluids to prevent dehydration.
Oral rehydration fluids can be used if mild dehydration occurs. Sports drinks can also be helpful to some extent. Severe dehydration may require hospitalization so that IV fluids can be used to replace body fluids rapidly.
Deaths resulting from norovirus are usually due to severe dehydration in the very young or very old. Early hospitalization can help ensure survival in this population.
The information here is intended as informational. It is important to do your own research and to understand that this article, and any others like it, should not be taken as medical advice, or as a replacement for medical advice.