Nausea and diarrhea? How to tell if it’s COVID, the stomach flu or food poisoning

Young man lying in bed, clutching his stomach

You wake up one morning with nausea and diarrhea. It gets worse throughout the day. You think you may have a stomach bug, but it's hard to know for sure. Maybe it's COVID-19 or even food poisoning?  

Nausea and diarrhea can have many causes. Determining the exact cause early on is not always simple.

The University Health Center explains the differences between these three common problems that can cause gastrointestinal issues.

COVID-19-related diarrhea and nausea

Nausea, vomiting and diarrhea are less common symptoms of COVID-19. Still, when they do occur, they tend to be some of the first symptoms you will experience. Diarrhea caused by COVID-19 tends to be more watery, yellow or green in color. It may be accompanied by cramping and bloating. If you have COVID-19, you will likely develop other symptoms within a day or two, such as fever, cough, congestion and/or loss of taste and smell.

If it's COVID-19, how long am I contagious?

If you are diagnosed with COVID-19, you are usually contagious up to five days from the start of symptoms. If youstill have symptoms after five days, stay away from others until your symptoms are gone. 

Stomach flu symptoms

What is often called the stomach flu actually isn't the flu at all. The actual name for the stomach flu is gastroenteritis. 

Gastroenteritis can be caused by viral, bacterial or parasitic infections but is commonly caused by norovirus. These infections cause inflammation in the gastrointestinal tract, decreasing the body's ability to absorb and digest food. The food moves so quickly through the GI tract that the acids the body secretes to break down the food don't have time to do their job, resulting in diarrhea. While the stomach bug is often called the 24-hour flu, most viral GI symptoms last between 24 to 72 hours.

Is stomach flu contagious?

Gastroenteritis is contagious through fecal matter or saliva. To help reduce infecting others, close the toilet lid before flushing, clean the bathroom and toilet frequently and wash your hands thoroughly and often.

Food poisoning symptoms

Food poisoning may be suspected if you have eaten out or traveled recently. Food poisoning is caused by eating food contaminated by bacteria, viruses or parasites. Symptoms typically develop within 12 to 36 hours and can last up to 72 hours. Blood in the stool  indicates that you may have food poisoning caused by bacteria and should be evaluated urgently. 

Is food poisoning contagious?

Individuals experiencing food poisoning can be contagious through fecal matter or saliva for up to 48 hours. To reduce transmission to others, follow the same suggestions as gastroenteritis: Close the toilet lid before flushing, clean the bathroom and toilet frequently, and wash your hands thoroughly and often. 

How to treat an upset stomach at home

There are several things you can do to help reduce the severity of symptoms, whether it’s caused by COVID-19, a GI virus or food poisoning:

  • Use over-the-counter anti-diarrheal medications that will help slow down the motility of the GI tract and/or take over-the-counter medications that will help reduce gas and bloating. These medications are available at the health center pharmacy at a discounted rate
  • Switch to a clear liquid diet such as juice, broth or popsicles or a bland diet with foods such as bread, rice or applesauce, depending on what your stomach can handle. Learn more about what to eat with an upset stomach

Diarrhea can cause you to lose a lot of water and electrolytes, which can lead to dehydration. That’s why it’s  crucial to stay hydrated and drink lots of clear fluids.

When to get help from a doctor

In most cases, you can let GI issues run their course. However, if you become extremely dehydrated, develop sunken eyes, high fever or blood in your stools, you should make an appointment at the University Health Center by calling 402.472.5000 Monday through Friday, between 8 a.m. and 4:45 p.m. or Saturday between 9 a.m. and  noon.