Shigella vs. Norovirus: What's the Difference Between These 'Stomach Bugs'?

If you’ve come down with a gnarly stomach bug recently, you’re not alone. The United States currently has a surge of infections by two pathogens that can cause uncomfortable digestive-related symptoms: Shigella and norovirus.

Norovirus cases hit a 12-month high in recent weeks, according to the Centers for Disease Control and Prevention (CDC). The agency has also reported a rise in Shigella infections (shigellosis)—particularly those that are alarmingly resistant to antibiotics.

While both Shigella and norovirus are commonly referred to as “stomach bugs”—as they do bear some similarities—they have some core differences in terms of transmission, symptoms, duration, and treatment.

What Is Shigella? Is It Dangerous?

Shigella bacteria typically circulate throughout the population year-round, according to Oladele Ogunseitan, PhD, MPH, a professor of population health and disease prevention at the University of California.

While antibiotics are the go-to treatment for a severe case of shigellosis, “there is a concern about an increase in antibiotic-resistant Shigella infections of diagnosed and reported cases,” Ogunseitan said.

According to the CDC, about 5% of Shigella infections reported were extensively drug-resistant in 2022, compared with 0% in 2015.

This stomach bug can cause dysentery, a type of severe diarrhea that contains blood or mucus.

In addition to diarrhea, other symptoms of a Shigella infection may include stomach pain, cramping, and fever. Shigella symptoms usually begin between one and three days after being exposed to the bacteria, and they can last up to a week. For immunocompromised people, these symptoms can persist for even longer, according to Luther Bartelt, MD, DTM&H, an associate professor of medicine at the UNC School of Medicine.

“Many episodes of Shigella can resolve on their own, and oftentimes go untested because the illness has run its course before a patient seeks medical care,” Bartelt said. “If we do detect it, and symptoms have been prolonged, and especially if it is causing dysentery, or if the patient has a compromised immune system, we typically treat with an antibacterial.”

Is Shigella Common? How Is It Spread?

In the U.S., an estimated 450,000 cases of shigellosis occur every year. Shigellosis usually affects children under the age of 5. But recently, the CDC noticed an increase in antibiotic-resistant Shigella infections among adults.

Shigella is highly contagious. The bacteria can live in the stools of infected people for up to a few weeks, even after their diarrhea has gone away. People can get infected if they swallow something that has come into contact with the stool of someone who’s infected. This can happen through sexual contact, eating contaminated food, or swallowing water while swimming.

To prevent transmission, the CDC advises washing hands with soap and water for at least 20 seconds after using the toilet, changing a child’s diaper, or assisting anyone with toileting.

What Is Norovirus? How Is It Different from Shigella?

Although norovirus is present at any time of the year, most norovirus outbreaks in the U.S. happen during winter months. It’s the most common foodborne illness in the country

Norovirus symptoms usually begin quicker than a shigellosis following exposure, ranging from 12 hours to two days. Like Shigella, it also causes diarrhea, but it’s often accompanied by nausea and vomiting, Bartelt said.

While antibiotics are used to treat severe cases of shigellosis, there’s no specific medicine for norovirus. Antibiotics also won’t work for norovirus because it’s a virus, not a kind of bacteria like Shigella. For those who are infected with norovirus, the CDC recommends drinking plenty of liquid to prevent dehydration.

“The only therapy for norovirus is rest and plenty of fluid intake,” Ogunseitan said. “For both, hygiene is extremely important, including frequent hand washing.”

Although both norovirus and Shigella are transmitted by fecal-oral routes, norovirus is particularly hardy on surfaces and it can be easily picked up by touching a contaminated surface such as a door handle, according to Bartelt.

Norovirus can also be transmitted through eating contaminated food or coming into direct contact with someone who’s infected. Norovirus symptoms only tend to last between one and three days, though immunocompromised individuals can be symptomatic for longer.