Shigellosis for Clinicians: Drug Resistance, Testing, Treatment and Complications

The main points

• Shigellosis often causes watery, bloody or prolonged diarrhea, abdominal pain, tenesmus (a constant urge to pass stool), fever and malaise.
• Lab tests can find Shigella in stool, and characterizing the isolate supports accurate diagnosis, targeted treatment, better outcomes and earlier outbreak detection.

A growing resistance problem

CDC estimates about 450,000 Shigella infections a year in the United States — the third most common bacterial intestinal infection — and about 242,000 of them are antimicrobial-resistant, a serious threat:

• multidrug resistance to trimethoprim-sulfamethoxazole, ciprofloxacin and azithromycin is widespread, in the U.S. and in parts of Asia and Africa;
• since 2017, CDC's National Antimicrobial Resistance Monitoring System has found a rising share of isolates resistant to both azithromycin and ciprofloxacin;
• resistant outbreaks have been reported in the U.S. and abroad.

Species and who is at risk

There are four species: S. sonnei, S. flexneri, S. dysenteriae and S. boydii. The last two are rare in the U.S. but still important where resources are scarce, and S. dysenteriae type 1 can be deadly.

Higher risk: young children, international travelers, gay, bisexual and other men who have sex with men, people experiencing homelessness, and people with weakened immune systems.

Spread: Shigella passes when people put in their mouths or swallow something that has touched the stool of an infected person. In 2019, reported incidence was 5.7 per 100,000. There's no marked season, reflecting person-to-person spread.

Testing and treatment

• Test the stool of patients with shigellosis-like symptoms, by culture or a culture-independent diagnostic test; if the latter is positive, confirm with culture.
• With resistance rising, do susceptibility testing if you plan to treat with an antibiotic.
• Shigellosis can be mild and self-limited. When treatment is needed, choose the drug by the isolate's susceptibility — or, in a local outbreak, the outbreak strain's; if treatment can't wait, use local resistance data.
• Recommended antibiotics: fluoroquinolones (such as ciprofloxacin), azithromycin, and third-generation cephalosporins (such as ceftriaxone); trimethoprim-sulfamethoxazole and ampicillin only if susceptibility is documented.
• For diarrhea lasting more than 3 days, follow-up stool cultures may be needed.

Stools are usually small in volume, and severe dehydration is rare. More: clinical care.

Complications

• Post-infectious arthritis — joint pain, eye irritation and painful urination, in about 2% of people infected with S. flexneri (rarely with other species). It can last months or years and become chronic, and occurs only in people genetically predisposed.
• Bloodstream infection — rare, from Shigella or other gut germs crossing a damaged intestinal lining; most common with HIV, cancer or severe malnutrition.
• Seizures — occasionally in young children, usually with high fever or abnormal electrolytes; they usually resolve on their own, and why they happen isn't well understood.
• Hemolytic-uremic syndrome — a toxin destroys red blood cells, usually with bloody diarrhea; with Shigella, only Shiga toxin–producing strains cause it, most often S. dysenteriae.

Resistance data: the monitoring system's BEAM Dashboard (human isolates) and the Food and Drug Administration's NARMS Now: Integrated Data.

Sources

Based on "Clinical Overview of Shigellosis," Centers for Disease Control and Prevention; a work of the United States government in the public domain. The source's "S. dystenteriae" is corrected to S. dysenteriae; its stock photograph is not reproduced.