The Four Symptoms of Gastrointestinal Illness, or GI


By Barry C. Fox, M.D.University of Wisconsin

Our guts are a miraculous system of food and nutrient processing, as well as waste disposal that would stretch out over 30 feet. It includes the esophagus, stomach, duodenum, all the way down through the small and large intestines. When this system is running smoothly, it’s like a well-oiled machine. However, when viruses, bacteria, or parasites enter the intestines, it’s a whole different story.

A visualization of the intestines.
Intestines are a complicated but smooth-running system, but can be affected by disease. (Image: sdecoret/Shutterstock)

Food Poisoning

Every year, one in six Americans gets sick from food poisoning, which also means—in all likelihood—once every five to six years you will be struck down by a foodborne illness. Several years ago, there was an educational lecture for a group of doctors at the equivalent of a 5-star restaurant. The evening lecture was completed, and all seemed to have gone well.

But six people who attended the lecture became ill within 12 hours. A quick epidemiological survey of the doctors revealed that each of them had consumed the mashed potatoes. They were most likely victims of food poisoning.

Staphylococcal Infection

There are a handful of bacterial conditions that can cause the rapid onset of intestinal illness less than 12 hours after food ingestion. It’s most likely that the guests at the lecture had staphylococcal food poisoning, and this was not an invasion of staphylococcal germs, but rather the ingestion of a pre-formed toxin that is not destroyed by heat or rewarming of the food.

In preparing the food, one of the food workers likely had Staph germs on their skin, which accidentally dropped into the mashed potatoes. There, the Staph germs found a nice, warm environment with all the necessary nutrients to replicate. Other foods implicated in Staph food poisoning include cream-filled pastries and custards. No antibiotics are indicated for treatment, as the illness usually resolves within 24 hours. So, even doctors can’t escape foodborne illnesses.

Learn more about the dynamic world of infectious disease.

Symptoms of Gastrointestinal Illness

A foodborne illness has three major causesbacteria, preformed bacterial toxins, and viruses. The four most prominent symptoms of a gastrointestinal illness or GI are various combinations of nausea, vomiting, diarrhea, and abdominal pain.

If you have some combination of our four symptoms complexes, you may have a foodborne illness. There are some key questions that will point in the correct diagnostic direction if foodborne illness is suspected, such as: What have you eaten in the last 48 hours? How soon after you ate did you feel ill?

People also often ask how you know if you’re sick from something that you ate. The general timeline of illness ranges from a few hours to a few days, so there is no definitive answer, but epidemiological clues need to be factored into the timeline.

This is a transcript from the video series An Introduction to Infectious DiseasesWatch it now Wondrium.

Vomiting and Nausea

First let’s tackle vomiting. A sudden onset of vomiting and nausea is likely due to the ingestion of a pre-formed toxin or chemical made by bacteria. Since the toxin is pre-formed, there is no risk of person-to-person spread. Nausea and vomiting interrupt the normal motility of the GI system.

An image of a young man experiencing nausea.
Nausea and vomiting are two of the common symptoms of gastrointestinal illness. (Image: New Africa/Shutterstock)

There is actually a vomiting center, called the area postrema, located in the lower portion of our brain. Input from the GI nervous system from noxious stimuli is transmitted to this brain location. Nausea is likely caused by an increased conscious awareness of activity in the vomit center.

Bacillus cereus

Another bacterium, Bacillus cereus, also produces a preformed toxin causing nausea and vomiting. Bacillus is typically found in starchy foods such as rice. A typical scenario for Bacillus food poisoning would be consuming leftover white rice from a restaurant. Either rice at the restaurant that was left over from the previous day or leftover rice that you placed in your refrigerator then partially rewarmed. Neither refrigeration nor rewarming affects the toxin.

With both Staph and Bacillus food poisoning, the diagnosis is usually made without a lab or blood test using these criteria, the right opportunity, the right food, and the typical illness. Nausea and vomiting are also the predominant symptom of the norovirus infection, which is the most common infectious cause of gastrointestinal illness in the United States.

Learn more about milestones in infectious disease history.


Next, let’s examine diarrhea as the major symptom. Diarrhea is defined as an increase in the frequency or volume of bowel movements that are unformed. All diarrhea has one abnormal physiological event in common—a mishandling of the absorption of water, especially in the colon.

Viral gastroenteritis accounts for another 30 to 40 percent of infectious diarrhea in the United States. One of the biggest culpritsagain through the fecal-oral routeis rotavirus. Rotavirus is the single most common cause of dehydrating diarrhea necessitating hospitalization in children under the age of 2.


About 3 million cases of rotavirus infection occur annually in the United Statesmostly from food contamination. The good news is that a childhood rotavirus vaccine has been shown to be effective in the United States, reducing the burden of this illness by more than 50 percent.

But worldwide, it’s astonishing to hear the statistics of children dying from diarrheathe toll is nearly 800,000 yearly for children under the age of 5, which makes diarrhea the second biggest killer of children in the world. While diarrhea doesn’t sound like something that should be life-threatening, for children who become dehydrated, it could mean the difference between life and death especially in impoverished areas of the world.

Dehydration Effects

The body needs a certain minimum volume of fluid in the arteries and the veins to keep the circulatory system pumping and an adequate blood pressure to support the function of major organs such as the heart, brain, and kidneys. Also, diarrhea can cause a major loss of key blood ingredients called electrolytes, especially sodium and potassium.

If the sodium and/or potassium levels of the blood become too low, muscles don’t function well, and, there is the potential for abnormal heart rhythms and even sudden death. Thus, rotavirus vaccination in underdeveloped countries is a key goal of the World Health Organization.

Common Questions about Food Poisoning and Viruses

Q. How many people in the US does food poisoning affect every year?

Every year, one out of six Americans are affected by gastrointestinal illness.

Q. What are the four major symptoms of gastrointestinal illness?

The four most prominent symptoms of gastrointestinal illness are various combinations of nausea, vomiting, diarrhea, and abdominal pain.

Q. What is the cause of 30 to 40 percent cases of gastrointestinal illness in the US?

Viral gastroenteritis accounts for 30 to 40 percent of infectious diarrhea in the United States. A major culprit is rotavirus.

Keep Reading
The Changing Outlook Toward Infectious Diseases
How Media Headlines Create a Frenzy Regarding Infectious Diseases
Seemingly Benign Infections of the 1950s in the US