Rising cases of drug-resistant Shigella in the U.S. and Canada have prompted public health authorities around the world to sound alarms about its spread. In fact, Ontario’s Chief Medical Officer of Health recently advised local public health units and clinicians to remain vigilant after 10 cases of resistant Shigella were reported in the province.

While the diarrhea-causing bacterium has been a known pathogen since the 1800s, it only recently developed resistance to the antibiotics that are used to treat it — something Dr. Jeffrey Pernica, a member of McMaster University’s Michael G. DeGroote Institute for Infectious Disease Research says is highly problematic.

Pernica, whose research also supports the Global Nexus for Pandemics and Biological Threats, has been studying Shigella in southern Africa for a decade. He says the bacteria has had significant effects in these resource-limited settings, and its growing resistance may only make things worse. The fact that resistant strains are now circulating locally, too, is what Pernica describes as “a major public health concern.”

We asked Pernica about the recent spread of Shigella, its growing resistance, and its pandemic potential. Here’s what you need to know.

What is Shigella?

Shigella is a group of bacteria especially common in low- and middle-income countries that frequently cause gastrointestinal infections — or diarrheal disease. Shigella infections, also known as shigellosis, do occur in Canadians in Canada; however, the majority of these infections are associated with travel. People who develop shigellosis while abroad often continue to shed infective bacteria in their stool for weeks after returning home.

These bacteria are transmitted via the fecal-oral route. In other words, people commonly acquire the infection through close contact with or consuming foods or liquids handled by an infected person who did not adequately sanitize their hands after toileting. People can also easily acquire shigellosis by changing the diapers of an infected infant or by touching contaminated items in a bathroom. Adults can also acquire shigellosis through sexual activity, especially that involving anal contact.

In low- and middle-income countries, Shigella causes an enormous amount of death and disability in young children, primarily because of how commonly these infections occur. Acute diarrheal disease is the second-leading cause of death in young children in non-industrialized countries and also causes serious growth failure and cognitive maldevelopment in these resource-limited settings. This is why shigellosis is a very big problem in many parts of the world. In Canada, Shigella is a rare cause of diarrhea in young children. When it does occur, it typically causes a few days of diarrhea and resolves itself without any treatment whatsoever. Some cases, though — especially severe cases with dysentery or bloody stools — require antibiotic treatment.

Many regional public health authorities around the world have been warning of a rise in cases of drug-resistant Shigella. Why has there been a recent uptick, and why is it of concern?

It has been well documented that antimicrobial-resistant bacteria are much more common in countries and regions where health systems rely heavily on broad-spectrum antibiotics. Many of these countries and regions are also those where shigellosis occurs more frequently. When Shigella infection is more common in a region where antibiotics are overused, the Shigella bacteria can become resistant to commonly used antibiotics. This is a real problem, because if standard antibiotics cannot be used to treat shigellosis, doctors must then turn to antibiotics that are more expensive, produce more side effects, and/or are delivered via the intravenous route.

It was only recently that the US Centers for Disease Control noticed an increase in drug-resistant Shigella. Five per cent of all submitted isolates in the US were shown to be resistant to all standard available oral antibiotics. It is not certain exactly why there has been an uptick in extensively drug-resistant strains in North America; however, it is likely tied to increases in drug-resistant Shigella in other parts of the world — COVID-19 showed us how easily infections can travel. Drug-resistant shigellosis is a problem because, to be treated effectively, it requires intravenous treatment or other non-standard therapies.

Does an increase in resistance give this bacterium pandemic potential?

I think most people think of a pandemic as a situation in which a highly transmissible disease — like COVID-19 — or a very deadly pathogen — like Ebola — spreads rapidly throughout a large population. In that sense, Shigella is unlikely to cause a pandemic, since it does not fulfil either of those criteria. Though Shigella is spread very effectively via contact, it still requires touch — it does not spread through the droplet or aerosol route like COVID-19. It can make people feel sick, but Shigella infections often self-resolve even without antibiotic therapy. Shigellosis only kills healthy individuals in very rare cases, unlike the Ebola virus. Having said that, just because it is unlikely to cause a pandemic doesn’t mean that it’s not a major public health concern.

What can people do to protect themselves from getting shigellosis?

Shigella is spread through personal contact via the fecal-oral route. Simply washing your hands prior to eating and ensuring that food and drink are not handled by infected individuals will be protective. If a family member is infected, ensure that they wash their hands well after toileting. Ensure also that non-infected individuals are not exposed to potentially contaminated items. If your sexual partner is infected, then it is important to avoid all sexual activity until at least a week after symptoms have resolved, and avoid anal contact for at least four to six weeks, given that Shigella can be shed in stools for a prolonged period.

Are there any vaccines available to help protect against Shigella?

Shigella infection is still relatively rare in North America; however, as noted, it is a scourge in many low- and middle-income countries. As such, there are vaccine candidates being developed to protect young children in resource-limited settings. Unfortunately, at this time, none are available in any jurisdiction. The best treatment for Shigella is antibiotics, which is obviously problematic for these extensively antibiotic-resistant strains.

What are some common symptoms to watch for, and when should you see a doctor?

Shigella commonly causes diarrhea, abdominal pain and fever. Bloody stools may or may not be present. Since most diarrhea in Canada is typically caused by viruses, people with non-bloody diarrhea really only need to seek medical attention if they become dehydrated or if they have knowingly had contact with someone who had a laboratory-proven parasitic or bacterial intestinal infection, like Shigella. Since bloody diarrhea is much more likely to be associated with an infection that requires specific treatment, anyone who suddenly develops bloody diarrheal stools should seek medical attention.