"An infected person literally sheds billions of viral particles, but it only takes one or two viral particles to infect someone," said Gemma Downham, the director of patient safety and infection prevention for AtlantiCare.
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And once infected, about a day or two later the sickness sets in.
"They become sick, and norovirus packs a punch. There's vomiting, diarrhea, stomach cramps. But just as fast as it comes on, it does tend to leave as well-- typically one to three days people are recovering," said Downham.
"It is extremely contagious, so it's really hard. Once it gets into your household, it's very hard to prevent the rest of the house from getting it," said Dr. Marci Drees, chief infection prevention officer with ChristianaCare.
Medical experts say prevention comes down to a tried and true technique.
"What's really important with norovirus is to wash your hands with soap and water. Norovirus isn't always killed by alcohol hand sanitizers. You need to actually wash it off with soap and water because it is spread through the fecal-oral route," said Downham.
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And she says to make sure to clean surfaces with a disinfectant that is approved against norovirus, like bleach.
"This is touching contaminated surfaces, and that's why you can pick it up in bathrooms. This is very prevalent in day care areas when there tends to be cases that come in," Downham said.
And the CDC recently raised the alarm on another stomach bug. This one though is bacterial, it is called Shigella.
"The CDC has identified some strains of this bacteria that are basically resistant to almost every antibiotic," said Drees said.
Shigella can have some similar symptoms to a common stomach bug or norovirus.
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"Norovirus tends to start off with a lot of vomiting, and then progresses to diarrhea, or sometimes they both start at once. Shigella tends to be more diarrhea and not so much vomiting. You might have stomach cramps," Drees.
So far, only a small amount of cases have been drug-resistant.
"Only 5% from what they've been able to sample. But that was zero six or seven years ago. So it's on the increase. So it's definitely worth being concerned about," said Drees.
Experts also say for both illnesses, staying hydrated is important.