Key points
- Patients with shigellosis often experience watery, bloody, or prolonged diarrhea, abdominal pain, tenesmus, fever, and malaise.
- Healthcare providers can order laboratory tests to identify Shigella germs in the stool of an infected person.
- Characterizing isolates can lead to more accurate diagnoses, targeted treatment (when needed), improved patient outcomes, and earlier detection of outbreaks.
Overview
CDC estimates about 450,000 cases of Shigella infection (shigellosis) occur in the United States every year; an estimated 242,000 of infections are antimicrobial-resistant. Antimicrobial-resistant Shigella infections are considered a serious threat for the following reasons:
- Multidrug resistance to trimethoprim-sulfamethoxazole, ciprofloxacin, and azithromycin is widespread in the U.S. and in other parts of the world, including Asia and parts of Africa.
- Since 2017, CDC's National Antimicrobial Resistance Monitoring System (NARMS) has detected an increasing percentage of Shigella isolates that are resistant to both azithromycin and ciprofloxacin.
- Outbreaks of antimicrobial-resistant Shigella infections have been reported in the United States and other countries.
Keep in mind
Types and strains
There are four species of Shigella:
- Shigella sonnei
- Shigella flexneri
- Shigella dysenteriae
- Shigella boydii
S. dysenteriae and S. boydii are rare in the United States, though they continue to be important causes of disease in areas with less access to resources. Shigella dysenteriae type 1 can be deadly.
At-risk populations
- Young children
- International travelers
- Gay and bisexual men and other men who have sex with men (MSM)*
- People experiencing homelessness
- People with weakened immune systems
How it spreads
Transmission of Shigella occurs when people put something in their mouths or swallow something that has come into contact with stool of someone infected with Shigella.
Infection rates
CDC estimates about 450,000 cases of shigellosis occur in the United States every year, making it the third most common bacterial enteric disease.
In 2019, the incidence of shigellosis in the United States reported to the National Notifiable Diseases Surveillance System was 5.7 cases per 100,000 individuals.
Shigellosis does not have a marked seasonality, likely reflecting the importance of person-to-person transmission. For more information, see the FoodNet Annual Report.
Testing and diagnosis
Healthcare providers can order laboratory tests to identify Shigella germs in the stool of an infected person. Testing the stool of patients with shigellosis-like symptoms is recommended. Characterizing isolates can lead to more accurate diagnoses, targeted treatment (when needed), improved patient outcomes, and earlier detection of outbreaks.
- When shigellosis is suspected, request a stool specimen for testing by culture or by a culture-independent diagnostic test (CIDT).
- If a CIDT is positive for shigellosis, confirm the diagnosis with a stool culture.
- Given the increasing rate of antimicrobial-resistant shigellosis, perform antimicrobial susceptibility testing if you plan to treat with an antibiotic.
- Shigellosis can be a mild, self-limited illness. When treatment is indicated, select an antimicrobial agent based on the susceptibility profile of the individual isolate or, during a local outbreak, on that of the outbreak strain. If antibiotics are needed before susceptibility results are available, select treatment based on local resistance data when available.
- Fluoroquinolones (such as ciprofloxacin), azithromycin, and third-generation cephalosporins (such as ceftriaxone) are recommended antibiotics. Trimethoprim-sulfamethoxazole and ampicillin are options if susceptibility is documented.
- If a patient has prolonged diarrhea (diarrhea lasting more than 3 days), follow-up stool cultures may be needed.
Symptom management
Patients with Shigella infection often experience watery, bloody, or prolonged diarrhea, abdominal pain, tenesmus, fever, and malaise. Stools tend to be of small volume, and severe dehydration is rare.
Complications
Possible complications from Shigella infections include:
- Post-infectious arthritis. A syndrome of joint pain, eye irritation, and painful urination after an infection is called post-infectious arthritis. This can happen in about 2% of people who are infected with S. flexneri. Few cases have been reported in association with S. sonnei or S. dysenteriae infection. It can last for months or years and can lead to chronic arthritis. Post-infectious arthritis is caused by a reaction to Shigella infection that happens only in people who are genetically predisposed to it.
- Bloodstream infections. Although rare, bloodstream infections are caused either by Shigella organisms or by other germs in the gut that get into the bloodstream when the lining of the intestines is damaged during shigellosis. Bloodstream infections are most common among patients with weakened immune systems, such as those with HIV, cancer, or severe malnutrition.
- Seizures. Generalized seizures have been reported occasionally among young children with shigellosis, and usually resolve without treatment. Children who experience seizures while infected with Shigella typically have a high fever or abnormal blood electrolytes, but it is not well understood why the seizures occur.
- Hemolytic-uremic syndrome or HUS. HUS occurs when bacteria enter the digestive system and produce a toxin that destroys red blood cells. Patients with HUS often have bloody diarrhea. When due to infection with Shigella, HUS is only associated with Shiga-toxin producing strains, most commonly S. dystenteriae.
- * The term "men who have sex with men" is used in CDC surveillance systems because it indicates men who engage in behaviors that may transmit Shigella infection, rather than how someone identifies their sexuality.