Shigella infection (shigellosis) is an intestinal disease caused by a family of bacteria known as shigella. The main sign of shigella infection is diarrhea, which is often bloody.

The Mayo Clinic


Image by AJC1 | Flickr

Shigella is a family of bacteria that causes the infectious disease shigellosis (also known as bacillary dysentery). The bacterium is classified into four species: shigella sonnei, shigella flexneri, shigella boydii, and shigella dysenteriae.

With about 450,000 total cases annually, Shigellosis is the third most common cause of food-borne illness in the US. It is also a seasonal illness, as most cases are reported between July and October. Shigella sonnei is the type responsible for the majority of shigellosis illnesses, accounting for roughly two-thirds of cases in the US each year.


One of the most easily transmitted bacteria in existence, shigella only needs about 10 bacteria to cause infection. People most often acquire shigellosis by ingesting another person’s fecal matter. Medical professionals state that the lack of basic hygiene (e.g., handwashing) leads to the majority of shigellosis cases. Certain sexual activities are a secondary cause.

The consumption of contaminated food can also result in infection, because foods that come into contact with human or animal waste can transmit the bacteria. Common daily activities, such as drinking contaminated pool water or consuming vegetables harvested from a contaminated field, can also cause people to fall ill.


Shigellosis symptoms generally surface within one to three days after exposure. Although, it is possible to acquire shigellosis and experience no symptoms—a condition known as asymptomatic shigellosis.  Symptoms will usually dissipate within a five-to-seven-day period.

The most common symptoms of shigella food poisoning are abdominal pain, diarrhea, fever, rectal spasms, stomach cramps, and tenesmus—a feeling of pressure to have a bowel movement with empty stomach contents. The diarrhea symptoms can be severe in nature.

Diagnosis and Treatment

A shigella infection requires laboratory examination of a stool sample for diagnosis. Examination of this sample also provides insight for treatment; specifically, what antibiotics can be used most effectively. This depends on the strain of shigella contained within the sample.

As with most types of food poisoning, the symptoms of shigellosis will usually subside without medical intervention. However, it is common to experience abnormal bowel movements for nearly a month after exposure.

Doctors commonly prescribe antibiotics to shorten the duration of the illness. This generally takes place shortly after the stool sample examination. Relatedly, some strains of the bacteria are resistant to antibiotics. Despite often severe diarrhea, anti-diarrheal medication is not normally prescribed as they can make symptoms worse.

Antibiotics commonly prescribed for shigella infection include ampicillin, ciprofloxacin, ceftriaxone, or sulfamethoxazole/trimethoprim (Bactrim). Over-the-counter treatment may include bismuth subsalicylate (Pepto-Bismol).


Image by isis325 | Flickr

Young children and the elderly are most at-risk for severe complications stemming from shigella. Complications of the illness include seizures, rectal bleeding, and severe dehydration. The bacteria can also enter into the blood stream, potentially causing death.

Toxic megacolon is a rare, yet serious, medical condition that involves paralysis of the colon. As a result of the colon’s paralyzed state, the individual cannot pass gas nor have a normal bowel movement. Abdominal pain, disorientation, fever, swelling, and weakness are common symptoms of this condition. Toxic megacolon can be fatal without medical intervention, because the colon will eventually rupture.

Older adults who contract shigella should watch for signs that they have developed reactive arthritis (Reiter’s Syndrome), which is the result of the immune system mistakenly fighting the body instead of the bacteria. The most common symptom—inflammation of the eyes, joints, or urinary or reproductive organs—usually surfaces a few weeks after initial exposure. This condition requires medical treatment.

Another rare yet serious condition resulting from a shigellosis infection is hemolytic uremic syndrome (HUS). The condition causes hemolytic anemia—the systematic destruction of red blood cells—and can result in kidney failure.


Proper hygienic habits, particularly hand washing, are crucial preventative measures against shigella infection. To mitigate the bacteria, basic food safety precautions, such as cleaning hands and surfaces, washing certain foods, and keeping food separate, will suffice. Individuals who have contracted shigella should not prepare food for others.

Other recommendations include the following:

– Consuming only boiled or treated water while traveling.
– Swimming only in pools maintaining the recommended chlorine levels.
– Avoiding pools that contain children not old enough to be toilet trained.