Shigellosis is a bacterial infection of the intestines that causes diarrhea, often bloody, along with fever and stomach cramps. It’s caused by Shigella bacteria, which spread remarkably easily. As few as 10 bacteria can trigger an infection, making it one of the most contagious foodborne illnesses. The CDC estimates about 450,000 cases occur in the United States every year, ranking it the third most common bacterial gut infection in the country.
How Shigella Spreads
Shigella bacteria live in the stool of infected people, and the infection passes from person to person through what’s called the fecal-oral route. In practical terms, this means you can get sick by touching a contaminated surface and then touching your mouth, eating contaminated food, drinking unsafe water, or having close contact with someone who’s infected. Sexual contact is another documented route of transmission, particularly during outbreaks among men who have sex with men.
What makes Shigella unusually dangerous compared to many other bacteria is its resistance to stomach acid. Most harmful bacteria get destroyed when they hit the acidic environment of your stomach, but Shigella survives that gauntlet. That’s why the infectious dose is so tiny: swallowing just 10 to 100 organisms is enough to make you sick. For comparison, Salmonella typically requires thousands or even millions of bacteria to cause illness.
Young children, older adults, people with weakened immune systems, and international travelers face the highest risk. Childcare settings are common sites for outbreaks because of diaper changing and the difficulty of enforcing handwashing among toddlers.
Symptoms and Timeline
Shigellosis typically begins one to two days after exposure. The hallmark symptoms are watery or bloody diarrhea, stomach cramps, and fever. Many people also experience a painful urge to have a bowel movement even when the bowels are empty, a sensation called tenesmus. Some infections produce only mild, watery diarrhea that’s easy to confuse with a stomach virus, while more severe cases involve frequent bloody, mucus-filled stools.
Most people recover in five to seven days without needing antibiotics. However, you should pay attention to warning signs: bloody diarrhea, diarrhea lasting more than three days, severe stomach cramping or tenderness, or a high fever. These suggest a more serious infection that may need treatment.
How Shigella Damages the Gut
Shigella doesn’t just sit in your intestines and produce toxins the way some bacteria do. It actively invades the cells lining your colon. The bacteria use a needle-like structure to inject proteins directly into intestinal cells, hijacking the cell’s internal scaffolding to pull themselves inside. Once in, they spread from cell to cell without ever re-entering the gut, essentially hiding from your immune system.
Your body’s inflammatory response to this invasion is what causes most of the damage. The immune system attacks the infected tissue, leading to the ulceration, bleeding, and mucus production that show up as bloody diarrhea. This tissue destruction is the price your body pays for fighting off the infection.
Diagnosis
Doctors diagnose shigellosis through a stool sample. The traditional method is a stool culture, where a lab grows bacteria from your sample and identifies the species. This remains the gold standard but can take a couple of days. Newer molecular tests using DNA amplification (PCR) can detect Shigella faster and may catch infections that cultures miss. Research has shown that PCR-based testing picks up more cases than culture alone, particularly in settings where quick identification matters for controlling outbreaks.
Lab testing also reveals which antibiotics the bacteria are susceptible to, which has become increasingly important as drug-resistant strains spread.
Treatment
Most cases of shigellosis resolve on their own with rest and fluids. Staying hydrated is the most important thing you can do, since diarrhea pulls water and electrolytes out of your body quickly. Bismuth subsalicylate (the active ingredient in Pepto-Bismol) can help with symptoms.
One critical point: do not take anti-diarrheal medications like loperamide (Imodium) if you have bloody diarrhea. These drugs slow gut movement, which can trap the bacteria inside your intestines and make the infection worse.
For severe cases, doctors prescribe antibiotics, which can shorten fever and diarrhea by about two days. The two most commonly recommended options are ciprofloxacin and azithromycin. If you’re prescribed antibiotics, finishing the full course matters even if you feel better partway through, because stopping early can contribute to resistance.
Drug Resistance Is Growing
Antibiotic resistance in Shigella is a serious and worsening problem. In 2015, the CDC recorded zero extensively drug-resistant (XDR) Shigella infections. By 2022, about 5% of reported infections were caused by XDR strains, meaning they resisted every commonly recommended antibiotic: azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole, and ampicillin.
Between 2015 and early 2023, the CDC documented 239 XDR isolates. Two-thirds were Shigella sonnei and one-third were Shigella flexneri. This trend is why lab testing to identify which antibiotics still work against a specific infection has become essential rather than optional.
Complications
Most people recover fully, but shigellosis can lead to serious complications in some cases. About 2% of people infected with certain Shigella types, most commonly Shigella flexneri, develop reactive arthritis afterward. This causes joint pain, eye irritation, and painful urination. It typically lasts three to five months, though in rare cases it persists for years. People with a specific genetic predisposition are most vulnerable.
A rarer but more dangerous complication is hemolytic uremic syndrome (HUS), which occurs mostly in children. HUS happens when the bacteria produce a toxin that destroys red blood cells, which then clog the kidneys’ filtering system and can lead to kidney failure. It’s most closely associated with Shigella dysenteriae, the most dangerous of the four Shigella species, and is the leading cause of death in outbreaks caused by that strain. The risk of HUS increases when the wrong antibiotics are used or when treatment starts more than four days after symptoms begin.
Prevention
Handwashing is the single most effective defense against Shigella. Wash your hands thoroughly with soap and water after using the bathroom, after changing diapers, and before preparing or eating food. Because the infectious dose is so low, even small lapses in hygiene can lead to transmission.
In childcare settings, prevention requires more structured effort. Diaper-changing areas should be physically separated from play and food preparation spaces. Children should wear clothing over diapers to reduce contamination. Staff who change diapers ideally should not be the same people preparing food. Toys, surfaces, and commonly touched objects need regular cleaning and disinfecting, especially during an outbreak. Shared water features like kiddie pools and water tables are breeding grounds for transmission and should be avoided in childcare programs.
When traveling to regions with limited sanitation, stick to bottled or treated water, avoid ice, and eat foods that have been thoroughly cooked. Shigella’s low infectious dose means that even brief exposure to contaminated water or food can be enough.