Answer: Do not send your child to school or day care for at least 3 days (72 hours) after symptoms have stopped (48 hours minimum).
People with stomach bugs are contagious for at least 3 days after symptoms have stopped. The viruses can remain in feces for even longer so hand washing after using the bathroom is extremely important. In an ideal world, your child needs to be well for at least 3 days before you send them back to school or day care. That means that it has been 72 hours since they last vomited or had diarrhea. If they are not eating normally and don't have normal poop, then they are still sick, are still contagious, and need to stay home.
Parents are often confused about how long to keep a child home from school after a vomiting illness. It is common today for parents to send their kids back to school or day care as soon as they are feeling better. This is the main reason the stomach viruses spread like wildfire. If you send them back to school only 24 hours after their last episode of vomiting or diarrhea, they will still be contagious and they may not even be done having vomiting or diarrhea. Children often have a relapse of vomiting after the 24 hour mark. Also, there can be delay between the vomiting and diarrhea halves of the illness. A child may be up all night throwing up, be fine the next day, and have the diarrhea start on the following day. My children have experienced a 24-hour period of calm between the vomiting and diarrhea halves of the illness. It would be a terrible idea to send your child to school during that time. (Not everyone gets diarrhea, though.) A microscopic spec of vomit contains millions of viruses and these specs fly far when someone vomits. So, if your child throws up in the middle of class, you are exposing all of the other students and teachers to the illness. If you knew your child was sick the night before and you sent them to school anyway, most people will be very angry with you.
48 hours is the absolute minimum amount of time to wait to be sure that your child is done being sick. Once my son had a virus where he vomited several times on Tuesday, was better on Wednesday, but vomited again on Thursday. He also had a diarrhea illness where he had went 40 hours between explosions. I thought he was fine until another one hit. During a stomach bug that traveled through our house in Jan/Feb 2012, my son Jon, vomited 3 times on Sunday. He had no symptoms on Monday but he hardly ate anything. Most other people would have sent him to school on Tuesday. I didn't because he wasn't eating. If the kid is not eating normally, they are still sick. Tuesday afternoon, he complained of bad tummy pains and took a nap. When he woke up he had a diarrhea explosion. It had been just over 48 hours where he didn't have any symptoms at all. I am so glad he wasn't at school when that happened.
Keep your child home until they are good and well. 48 hours is the minimum amount of time it takes for you to be sure your child is actually done having symptoms. 72 hours is the minimum amount of time that they will be contagious. If you have an older child and you can only keep him home for 2 days because he has a big test, make sure he understands the importance of hand washing. If you have a preschooler, keep them home even longer!
Do not take your child to unnecessary places until they have been well for 2 weeks. Do not go to birthday parties, indoor playgrounds, playgroups, nursing homes, friend's houses, or swimming pools until they have been well for 2 weeks. In a swimming pool, tiny traces of virus filled feces are whisked away from you child’s bottom and float in the pool until another unsuspecting child swallows a mouthful of water. 24-48 hours later that child is sick. If parents just kept their kids home for a few days after the stomach flu, we all wouldn’t have to get it so often!
It is very important to clean with a product that actually kills norovirus when a stomach bug is in your home such as chlorine bleach or the Clorox® Hydrogen Peroxide Spray and Clorox Hydrogen Peroxide Wipes.
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--Annie Pryor, Ph.D.