How is the stomach flu transmitted (norovirus and others)?

Answer: You catch a stomach bug when germ-infested feces, vomit, nasal secretions, or saliva get into your mouth.

"Stomach flu" is just a nickname for viral gastroenteritis. It is not related to influenza, the real flu.The stomach bugs are highly contagious and are primarily spread through the fecal-oral route. Technically, you need to swallow the virus to get the illness. When a person has viral gastroenteritis, massive quantities of the viruses are present in their feces and vomit. These viruses easily get all over the toilet and bathroom. If another person accidentally swallows a few of these viruses, they get sick. Anything that you put into your mouth that has the viruses on it, can make you sick. (Food, your fingers, pen cap, toothbrush, etc.) The viruses remain in feces for at least 3 days after the person is well. Norovirus has also been shown to be in saliva samples of people for a few days after symptoms have stopped too. Rotavirus has been shown to be present in nasal secretions.

Improper Hand Washing

The main reason these viruses spread like wildfire is thought to be improper hand washing. We aren’t washing our hands good enough after we go to the bathroom or change a diaper. Here are some examples of how the stomach flu can be spread by dirty hands. A person who is ill or contagious and uses the bathroom can leave some viruses on the faucet, flusher, toilet seat, or hand towel to wait for the next person. A restaurant or cafeteria worker who is contagious with a stomach virus, can start an outbreak by chopping lettuce with a microscopic fleck of feces under her fingernail. Diaper changing is another easy way to spread illnesses. Just think about all the things you touch after you change the baby's diaper BEFORE you wash your hands--especially if you have a kicking, twisting 1-year old. You touch the baby's clothes, the box of wipes, maybe a door knob, a light switch, your sleeves, and the faucet. A few of the viruses on your sleeve dry and fall onto your sandwich later that day. 48 hours later you are sick. It is hard to do a perfect hand washing. So, if you or a family member actually has a stomach bug, I would recommend wearing disposable gloves as much as possible. Also, you might want to have a hand sanitizer that kills norovirus such as Clorox Hand Sanitizer Spray or Zylast. For more hand sanitizer suggestions, read this page.

Viruses are easily spread all over the house.

I know what you are thinking. The last time someone in your house got the stomach flu, you washed your hands till they bled and you still got sick. This is partly because when a person (especially a child) is sick with viral gastroenteritis, the vomit and diarrhea get a whole lot of other places besides hands. Their clothes get covered and perhaps the carpet and toys. When the viruses are all over the place like that, it is hard to prevent other people in the house from catching the illness. It is hard to clean up every microscopic spec of vomit. If the sick person is an adult who makes it to the toilet, you have a good chance of containing the virus. But when it is a child who vomits in the middle of the family room, it is very difficult. Make sure to read the page about cleaning products that kill norovirus including Clorox Hydrogen Peroxide Wipes. In addition, your clean laundry is NOT sterile. I have done experiments that show that there are still live bacteria in clean laundry even after washing on hot and putting it in a hot dryer. I imagine that some viruses would survive that as well. Wash laundry that has vomit or diarrhea on it with chlorine bleach if possible. If you can't use bleach, I would wash all sick laundry 2 times AND make sure to wear disposable gloves when transferring the laundry from the washer to the dryer.

Stomach flu viruses can be temporarily AIRBORNE!

Norovirus has also been shown to become temporarily airborne when a person vomits. This is most likely true for the other gastroenteritis viruses as well. In one study, a person vomited in a hotel dining room. People eating at other tables all over the room got sick which could not be explained by direct contact. People at closer tables were more likely to be sick than people whose tables were farther away1. In another study, researches collected air samples in hospital room of people with norovirus and found viruses in the air most of the time. So, if your child vomits in the middle of the family room carpet, it is very easy for everyone to be exposed. People can breath in and swallow the temporarily airborne viruses. When the virus settles out of the air people can touch contaminated surfaces and then put their fingers in their mouth. For example, the viruses can land on the TV remote control. When you are flipping channels and eating popcorn, you may eat the virus.

It stands to reason that if virus particles can be aerosolized when a person vomits, the same phenomenon can occur when a person has explosive diarrhea. I have no scientific evidence to back me up, but I suspect that when you walk into a bathroom that smells horrid from a person having diarrhea, there may also be viruses in the air.

Norovirus can be present in saliva, unfortunately.

Everyone else, including the CDC, will tell you that norovirus is only present in vomit and diarrhea. However, norovirus is probably present in saliva in some people. Here is a research article that checked saliva samples from a family of 6 who all had norovirus. They took saliva samples every morning for 18 days and checked them for norovirus using RT-PCR. You won't be able to read the entire article unless you buy it. I bought it. The results show that all 6 family members had norovirus present in their saliva for 9-13 days after the vomiting STOPPED from norovirus! 2 of the family members who never had vomiting (only diarrhea) still had norovirus present in their saliva for 10 and 13 days!!! That is really, really upsetting. I could only find one research article that investigated this. Hopefully, more research will be done so we can be certain of how scared we need to be. Rotavirus has also been shown to be present in nasal secretions2,3,4. Therefore, people coughing and spitting when they talk can contribute to the spread of norovirus and rotavirus.

Contaminated Food and Water

Viral gastroenteritis is often spread through contaminated food and water. Third World countries with poor sanitation are ravaged by these illnesses. Here in the United States we generally have clean municipal water (I don’t want to think about the fact that our drinking water is not regularly tested for these viruses) but we still have an occasional problem with food6. Shellfish harvested from waters contaminated with sewage are frequently the cause of norovirus outbreaks. Fresh fruits and vegetables irrigated with water contaminated with sewage have caused outbreaks7. If a restaurant or cafeteria worker is contagious with viral gastroenteritis, they can easily contaminate your food. If several people get sick 2 days after a family reunion, it may not be that the potato salad was left in the sun too long. It may be that Aunt Frieda is getting over the stomach flu, and her potato salad was contaminated with her virus. When these viruses are transmitted through food it is called food borne illness. It is a type of food poisoning that is contagious.

If you would like to write to me or share your story, please email me. phd.annie at This is completely unrelated, but please check out the adorable books my 8 year old daughter wrote, illustrated, and published. Princess Katie and the Fairy Tea Party

and Princess Katie and the Mermaid Lagoon are available on amazon. They are wonderful stories about kindness, including others, and doing the right thing.

--Annie Pryor, Ph.D.

--Annie Pryor, Ph.D.

Viewer Comments

Birthday Parties!

My now 10-year-old had a 6th birthday party I will never forget! Her friend (a boy) had had it a few days prior to the party. The mom called me the day before and told me (which was nice...not all moms would think to do that!), then asked if it was ok for him to come. Back then, I wasn't educated about it like I am today and said...yes! The morning of the party, the mom called to say that only he was coming, because she now had it!

Needless to say, despite being SO careful -- only the adults handled ALL the food (although they were all over the downstairs of my house and played with and touched many toys and surfaces) and my crazy Lysoling and cleaning after the party was over, almost 24-hours later to the minute, both of my kids started throwing up! One by one, other moms called to say that their kids were sick, too.

Obviously, I have now learned from my mistakes back then (I should've said NO to him coming in the first place, for one thing!), but the point of my story is that I am convinced that everyone got sick because this boy didn't wash his hands properly after pooping!!

If everyone would JUST FREAKIN' WASH THEIR HANDS THOROUGHLY after going to the bathroom, the world would be a much healthier place. :)


Stomach flu viruses must have been present in my saliva.

Two weeks ago I got really sick really fast. My children and husband left the house for two days. I cleaned with bleach, lysol, clorox wipes very thoroughly. I got sick on a saturday night around 10pm and stopped getting sick the next day (sunday) at 1pm. They returned on Monday afternoon. Tuesday my youngest daughter took ice out of my cup and ate it. Tuesday night my husband drank after me. Thursday at 6 my youngest daughter that drank after me got terribly sick and my husband the same night 4 hours later. Most interesting is that my husband got sick 4 hours after my daughter and my daughter ate the ice about 4 hours prior two days earlier. My older daughter never drank after me and did not get this violent stomach virus. (she ended up throwing up a week later but only once due to strep throat - i never knew that could cause vomiting).

Thought you would find my story interesting because it proves we are contagious for days, and it was present in my mouth and transmitted that way and not fecal oral.


My family went to 2 birthday parties in January 2009 where a child threw up. Amazingly, my family did not catch it either time. I'm not sure if anyone else got it from the first party. I have more information on the second party since it was a family party. There were about 30 people at the party when the birthday boy threw up. 5 people (2 kids and 3 adults) came down with the stomach flu a few days later. I feel very lucky that we did not get sick. I just want to tell everyone that it is possible to escape the stomach flu even if you are at a party where someone gets sick. So, don't panic.


My 8-year old son threw up on our hardwood floor on his way to the bathroom. I cleaned it up with clorox clean-up that contained bleach. I wore rubber gloves and threw away the pants I was wearing. My 2 younger children were already in bed for the night so I thought if I cleaned good enough, they wouldn't catch it. My sick son stayed in his room for the next 2 days and never saw my two younger children. Unfortunately, 36 hours after my 8-year old threw up, my 3 year old started throwing up and my 1 year old had diarrhea. So, it is either impossible to clean good enough, or 2 younger children caught the virus from my 8-year old before he had any symptoms.