Extensively drug-resistant Shigella infections are increasing. Here’s what you need to know.

Anthony Maurelli Profile Image
UF professor of environmental and global health, Anthony Maurelli, Ph.D.

The Centers for Disease Control and Prevention issued a recent warning about increasing rates of extensively drug-resistant shigellosis, a gut disease caused by Shigella bacteria. Shigellosis is rarely life-threatening and most people do not need treatment. But the increase in extensively drug-resistant strains is worrisome because it leaves fewer treatment options for those who need one.  

In 2015, there were no reports to the CDC of extensively drug-resistant shigellosis. But by 2022, 5% of all shigellosis cases were extensively drug-resistant. While this may not sound like a huge increase, with global travel connecting more people, public health officials are concerned about its potential to spread.

Colon of Monkey After Oral Challenge with Virulent strain of Shigella flexneri; tissue damage visible.
Intestinal tissue of a monkey with visible tissue damage from infection with a virulent strain of Shigella flexneri. (from LaBrec et al. 1964. J. Bacteriol. 88:1503).

Extensively drug-resistant shigellosis is not curbed by three different classes of common antibiotics — macrolide, quinolone and cephalosporins — and it does not respond to common antibiotic alternatives. Researchers are in the process of developing effective treatments. Antibiotics from the carbapenem class may be useful, according to Emerging Pathogens Institute Director J. Glenn Morris, Jr., M.D.

To learn more, we spoke with Anthony Maurelli, Ph.D., a professor and associate chair in the Department of Environmental and Global Health at the UF College of Public Health and Health Professions. Also a scientist at the EPI, Maurelli is a research expert in disease-causing bacteria, including Shigella.

What are the most common symptoms of shigellosis?

The symptoms include fever, stool that contains blood and mucus, diarrhea, cramping and an urgent feeling that you need to move your bowels when there’s really nothing to move. The reason you experience these symptoms is that the bacteria are invading and destroying the tissues that line the large intestine. The disease is very uncomfortable, but most shigellosis cases are not life-threatening.

How does shigellosis spread?

Shigellosis is transmitted via the fecal-oral route, that is, when bacteria in feces are swallowed by someone. Shigella is shed in feces, so consuming food or water contaminated with fecal matter containing Shigella is a major way that shigellosis is spread. People recovering from shigellosis may continue to shed Shigella in their feces for several weeks after symptoms are over. So it is important that they pay attention to good hygiene even after they start feeling better. Shigellosis can also be a sexually transmitted infection.

Shigella bacteria are closely related to the common gut microbe, E. coli, which does not cause disease. We researchers like to refer to Shigella as “E. coli with an attitude” because they are very good at living inside of us and skillful at causing disease. You only need to ingest a small number of bacteria to get sick.

How is shigellosis treated?

For most people, the disease resolves itself without treatment. We don’t even know if someone has the drug-resistant strain unless certain clinical tests are done. Healthy individuals with working immune systems generally do not require antibiotics.

Human cells in a laboratory culture infected with Shigella flexneri, which arevisible as dark blue stained rods. Shigella leads the host cell to change shape and form long extensions with Shigella at the ends. (Credit: Tony Maurelli)

But for people with compromised immune systems, children under five and the elderly, antibiotics may be recommended by a clinician to shorten the length of illness. This reduces the amount of infectious bacteria coming out of the individual, which helps protect others around them.

How can people manage their risk for developing a Shigella infection?

We’ve worked with Shigella in my laboratory for 40 years now. The first instructions I give my staff are to keep their hands away from their face and keep their fingers out of their mouth. Those are good words of advice for anyone to protect against infections that are transmitted through the fecal-oral route.

Proper hygiene habits are also very important. In the U.S., a lot of shigellosis cases occur in daycare centers where young children with poorly developed toilet habits can easily spread the disease. That’s why it’s very important that any child who has diarrhea be excluded from daycare centers until they’ve cleared the infection.

Foods such as leafy vegetables, or even fruits, that were irrigated with water contaminated with human feces may contain Shigella. Washing vegetables will generally get rid of at least the surface organisms if there’s potential contamination.

While we tend to think of Shigella as being a diarrheal disease, it is also a sexually transmitted infection. The CDC cited men who have sex with men as a group that has been particularly affected by shigellosis. The CDC offers additional steps that can help limit the transmission of Shigella bacteria during sexual activity.

Why might drug-resistant Shigella infections be on the rise?

In general, we’re seeing a rise in drug resistance in bacteria that cause disease because we use a lot of antibiotics in both veterinary medicine and in human health care. Overuse of antibiotics leads to the development of resistance mechanisms because existing treatments rarely kill every single bacterium, some remain and spread their resistance genes.  

In addition, bacteria that have acquired genetic tools to resist antibiotics can exchange these tools with one another — even with other closely related species of bacteria.

Human cells in a laboratory culture infected with Shigella flexneri. The bacteria are visible as dark gray rods inside the host cells. (Credit: Tony Maurelli)

That’s why these extremely drug-resistant strains of Shigella are concerning. There is a dearth of new antibiotics in the drug development pipeline. Correct stewardship of antibiotics is one of the tools that we still have to slow down the spread of these extremely drug-resistant bacteria.

What is your lab learning about Shigella bacteria now?

We have identified strains of Shigella bacteria that produce Shiga toxin, which cause harmful symptoms apart from shigellosis, such as hemorrhagic fever and kidney damage. One hypothesis we would like to test is whether the gene that produces this toxin enables Shigella bacteria to live in a reservoir outside of human hosts, such as contaminated water.

We found over 50 individuals infected with Shigella strains that tested positive for Shiga toxin had recently traveled to Haiti or the Dominican Republic. It would be interesting to check water sources in these locations for Shiga toxin-producing Shigella.

Written by: Natalie Van Hoose | Edited by: DeLene Beeland