Answer: A person is still contagious for at least 3 days after symptoms have stopped.
A person is contagious starting from the moment they start to feel sick and possibly even a little bit before that. In one study, Noroviruses were detected in the stool 15 hours after the people ingested the norovirus1. Usually symptoms don't start until 24-48 hours after ingestion. So, if people don't wash their hands well after using the bathroom, they can spread the germs to others before they even know they are going to get sick. People are contagious for at least 3 days after all stomach flu (viral gastroenteritis) symptoms have completely stopped and they feel perfectly fine2. That means that even when they feel fine they still have the virus in their stool for at least 3 days. Studies have shown that the viruses can be present in the stool for two weeks and sometimes longer so a person can be contagious even longer3. If your child suffered from Rotavirus, they are definitely contagious for 2 weeks or more4. Norovirus can remain in your feces for a month!5 This is why it is so important to wash you hands well after you go to the bathroom and keep you bathroom clean. Be considerate of others and stay away from other people as much as possible while you are contagious. That means that you must skip your best friends birthday party or New Years Eve party if you had the stomach flu 2 days ago. You should even skip visiting your grandmother on Christmas day if you were recently sick. She would not appreciate the present you would most likely be giving her.
My in-laws had a bad case of the stomach flu on December 18-19, 2009. They were well by December 20. They had relatives come visit for Christmas on December 26 (1 week later). 3 of the visitors came down with the same stomach flu starting about 36 hours after arriving. My in-laws never got sick again since it was the same virus they just had. So, 1 week is NOT long enough to wait. People and houses are still contagious! Everyone was mad at me for refusing to go visit on December 28 like we had planned.
Everyone asks me if the viruses that cause the stomach flu are present in saliva. The answer is that no one knows. No one has ever done the experiments. No one has taken saliva samples from people about 24 hours after they last vomited from the stomach flu and analyzed the samples for the presence of the viruses. I have searched high and low for papers describing these experiments and can't find any. I have contacted promenant norovirus researchers and no one thinks these experiments have been done. If anyone knows of these experiments, please let me know.
--Annie Pryor, Ph.D.
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.