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 are symptoms that can have a number of causes that include COVID-19, the stomach flu or food poisoning," says Ashley Barajas, FNP, Nebraska Medicine nurse practitioner. "Determining the exact cause early on is not always that cut and dry."

Barajas helps explain the differences between these three common problems that can cause gastrointestinal problems.

COVID-19-related diarrhea and nausea

"Nausea, vomiting and diarrhea are less common symptoms of COVID-19, but when they do occur, they tend to be some of the first symptoms you will experience," says Barajas. "There is no definite way to tell early on what is causing your symptoms, however, diarrhea caused by COVID-19 tends to be more watery, yellow or green in color and 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 you are still having symptoms after five days, stay away from others until your symptoms are gone, says Barajas. 

Stomach flu symptoms

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

Gastroenteritis can be caused by viral, bacterial or parasitic infections, but is commonly caused by the norovirus. These infections cause inflammation in the gastrointestinal tract which decreases the body's ability to absorb and digest food, explains Barajas. 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, says Barajas.

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 frequently, says Barajas.

Food poisoning symptoms

Food poisoning may be suspected if you have eaten out or traveled recently. Food poisoning is caused by eating food that has been 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 is also an indication 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 frequently, says Barajas. 

How to treat an upset stomach at home

To help reduce the severity of symptoms, whether it's caused by COVID-19, a GI virus or food poisoning, Barajas recommends using over-the-counter anti-diarrheal medications that will help slow down the motility of the GI tract. You can also take over-the-counter medications that will help reduce gas and bloating. Barajas also suggests switching 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 is able to handle. Learn more about what to eat with an upset stomach. 

"It is extremely important that you do the best you can to stay hydrated," says Barajas. "Diarrhea can cause you to lose a lot of water and electrolytes, which can lead to dehydration."

What if I'm pregnant or nursing?

Staying hydrated is even more important if you are pregnant to avoid dehydration and nutrient deficiency. Both can put undue stress on the fetus. If you are nursing a baby, dehydration will reduce your milk supply, notes Barajas.

When to get help from a doctor

In most cases, you can let GI issues run their course, says Barajas. However, if you become extremely dehydrated, develop sunken eyes, high fever or blood in your stools, you should make an appointment to see your doctor. 

"In the case of gastroenteritis or food poisoning, you may have a pathogen that requires additional antibiotic treatment," says Barajas.