Shigella infection, also called shigellosis, is a bacterial infection of the intestines that causes severe diarrhea, fever, and stomach cramps. It spreads easily through contaminated food, water, or direct contact with an infected person. Treatment focuses on rehydration and letting the infection run its course, though antibiotics may be needed in severe cases.
What Exactly Causes a Shigella Infection?
Shigella bacteria cause the infection. There are four main species of this bacteria. Shigella sonnei causes most cases in the United States. Shigella flexneri is more common in developing countries.
The bacteria enter your body through your mouth. This happens when you swallow even a tiny amount of contaminated stool. It does not take much. Fewer than 100 bacteria can make you sick. That is a very small number compared to other foodborne germs.
Common ways people get infected include:
- Eating food prepared by someone who did not wash their hands after using the bathroom
- Swallowing contaminated water from pools, lakes, or untreated wells
- Touching a contaminated surface and then touching your mouth
- Changing a diaper of an infected child and not washing hands properly
The CDC reports that shigellosis causes about 450,000 cases in the United States each year. Young children between ages 1 and 4 are most likely to get infected. Outbreaks also happen in daycare centers, nursing homes, and among men who have sex with men.
What Are the First Signs of a Shigella Infection?
Symptoms usually start one to three days after exposure. The first sign is often watery diarrhea. This can quickly turn into diarrhea that is bloody or contains mucus.
Other common symptoms include high fever, stomach cramps, and a constant feeling that you need to have a bowel movement even when your colon is empty. Doctors call this tenesmus. It can be very uncomfortable.
Most people recover within five to seven days without medical treatment. But some groups are at higher risk for complications. These groups include young children, older adults, and people with weakened immune systems.
Dehydration is the most common complication. Severe dehydration from shigellosis can require hospitalization. In rare cases, the infection can cause seizures in young children or a condition called hemolytic uremic syndrome that damages the kidneys.
How Is a Shigella Infection Diagnosed?
Doctors diagnose shigellosis with a stool test. They send a sample of your stool to a lab. The lab looks for Shigella bacteria growing in a culture. Results usually take two to three days.
Blood tests are not typically needed. But your doctor may order one if you have severe dehydration or signs of a bloodstream infection. This is rare.
The CDC recommends testing if you have bloody diarrhea, if you are part of an outbreak, or if you work in food service or childcare. Testing helps public health officials track where the bacteria are spreading and which antibiotics still work against them.
Antibiotic resistance is a growing concern. Some Shigella strains no longer respond to common antibiotics like ciprofloxacin or azithromycin. The CDC tracks these resistant strains closely. Your doctor may need to test which antibiotic will work for your specific infection.
What Is the Best Treatment for a Shigella Infection?
Treatment depends on how sick you are. For mild cases, the main treatment is rehydration. Drink plenty of fluids that contain water, salt, and sugar. Oral rehydration solutions available at pharmacies work well. Sports drinks are a reasonable alternative for mild cases.
Most people do not need antibiotics. The infection clears on its own within a week. Antibiotics can shorten the illness by about two days. But they also contribute to antibiotic resistance when used unnecessarily.
Your doctor may prescribe antibiotics if:
- You have severe symptoms like high fever or bloody diarrhea
- You have a weakened immune system
- You work in food service or childcare
- You live in a group setting like a nursing home
Azithromycin and ceftriaxone are common first choices. The specific antibiotic depends on local resistance patterns. A study published in the journal Clinical Infectious Diseases found that about 5% of Shigella cases in the U.S. are resistant to all recommended antibiotics. This number is rising.
Do not take antidiarrheal medications like loperamide (Imodium). They can make the infection worse by keeping the bacteria in your gut longer. They also increase the risk of complications.
How Does Shigella Infection Compare to Other Causes of Diarrhea?
Many illnesses cause diarrhea. Knowing the difference helps you decide if you need to see a doctor. The table below compares shigellosis to other common causes.
| Condition | Cause | Key Features | Typical Duration |
|---|---|---|---|
| Shigellosis | Shigella bacteria | Bloody stool, fever, tenesmus | 5-7 days |
| Salmonellosis | Salmonella bacteria | Diarrhea, fever, cramps | 4-7 days |
| Norovirus | Virus | Vomiting, watery diarrhea, no blood | 1-3 days |
| Campylobacter | Campylobacter bacteria | Bloody diarrhea, severe cramps | 5-10 days |
| Traveler’s diarrhea | E. coli or other bacteria | Watery diarrhea, cramps | 3-5 days |
Blood in the stool is a red flag. It suggests a bacterial infection like Shigella or Campylobacter rather than a virus. If you see blood in your stool, call your doctor. You may need a stool test.
Shigella is also more likely than other bacteria to spread from person to person. The infectious dose is very low. This is why outbreaks happen so quickly in group settings.
How Can You Prevent a Shigella Infection?
Prevention comes down to hand hygiene. Wash your hands thoroughly with soap and water after using the bathroom, changing a diaper, and before preparing food. Hand sanitizer helps but is not a replacement for soap and water against Shigella.
If you or your child has shigellosis, stay home from work, school, or daycare until the diarrhea has stopped. The CDC recommends waiting at least 48 hours after the last episode of diarrhea before returning to normal activities. This reduces the chance of spreading it to others.
Do not prepare food for others while you are sick. The bacteria can survive on surfaces for several days. Clean bathrooms and high-touch surfaces with a bleach-based cleaner.
Swimming pools are a common source of outbreaks. Avoid swimming if you have diarrhea. Shigella can survive in chlorinated water for up to 30 minutes. The CDC reports that about 1 in 5 recreational water outbreaks are caused by Shigella.
There is no vaccine for shigellosis yet. Several vaccines are in clinical trials. But as of 2026, none are approved for use. Good hygiene remains the only reliable prevention.
Common Misconceptions About Shigella Infection
Some people believe that shigellosis is the same as food poisoning from a bad meal. It is true that contaminated food can spread Shigella. But person-to-person spread is actually more common. You are more likely to get it from a sick family member than from restaurant food.
Another myth is that antibiotics always cure shigellosis quickly. This is not true for resistant strains. Some people take a full course of antibiotics and still have symptoms. Their doctor may need to switch to a different antibiotic based on lab results.
Some people also think that once you have had shigellosis, you cannot get it again. This is false. You can be reinfected with a different strain of Shigella. The immunity from one infection does not protect against all four species.
Finally, many people believe that diarrhea always needs medication to stop. For shigellosis, letting the diarrhea run its course is safer than stopping it with antidiarrheal drugs. The body uses diarrhea to flush out the bacteria. Blocking this process can prolong the illness.
Frequently Asked Questions
How long is a shigella infection contagious?
You are contagious from the moment symptoms start until about two weeks after you recover. Some people carry the bacteria for several weeks without symptoms.
Can you treat shigella at home without a doctor?
Mild cases can be managed at home with rest and oral rehydration. See a doctor if you have bloody diarrhea, a fever over 102°F, or signs of dehydration like dry mouth and dark urine.
Is shigella the same as E. coli?
No, they are different bacteria. Both can cause bloody diarrhea, but Shigella spreads more easily from person to person and requires fewer bacteria to cause infection.
What foods are linked to shigella outbreaks?
Any food that is handled by an infected person can spread shigella. Common sources include raw vegetables, salads, sandwiches, and unpasteurized milk.
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