Shigellosis is an acute intestinal infection caused by Shigella bacteria — transmitted by the fecal-oral route with one of the lowest infectious doses of any bacterial pathogen (as few as 10 organisms). It causes bacillary dysentery: acute bloody diarrhoea, abdominal cramps, fever and painful tenesmus. Global burden: approximately 188 million cases and 600,000 deaths per year — predominantly in children under 5 in LMICs. It is also a significant cause of travellers' diarrhoea, outbreaks in childcare settings, and — in high-income countries — an increasingly recognised MSM STI.

What are the Shigella species and how do they differ?

Four Shigella species cause human disease: S. sonnei (most common in HICs — generally less severe, self-limiting); S. flexneri (predominant in LMICs — causes most severe dysentery, more antimicrobial resistance); S. boydii (less common); S. dysenteriae (least common — type 1 produces Shiga toxin, causes the most severe disease including HUS, has epidemic potential). S. sonnei is increasingly prevalent globally as sanitation improves (HICs) while S. flexneri declines.

How is shigellosis treated?

Mild to moderate: ORS (oral rehydration salts) + careful food/fluid intake; antibiotics shorten duration and prevent spread but are not always required. Antibiotic choice depends on local resistance: azithromycin (1g single dose — increasingly preferred due to fluoroquinolone resistance); ciprofloxacin (500mg BD × 3 days — if susceptible); ceftriaxone (for severe disease or MDR). WHO advises antimicrobial susceptibility testing where available. Do NOT use antidiarrhoeals (loperamide) — may worsen invasive disease and prolong shedding.

Why is shigellosis an AMR crisis?

Shigella has developed resistance to every antibiotic introduced as first-line treatment. Currently: >90% of Shigella isolates in many countries are resistant to ampicillin and TMP-SMX (historical first-line agents). Fluoroquinolone (ciprofloxacin) resistance has risen from 50% in multiple Asian, African and Middle Eastern settings. Azithromycin resistance is increasing. ESBL-producing Shigella (resistant to ceftriaxone) is documented. Limited treatment options make effective case management increasingly difficult — underscoring the urgency of Shigella vaccine development.

Is a Shigella vaccine available?

No Shigella vaccine is currently licensed. However, WHO has designated Shigella as a high-priority pathogen for vaccine development — given its scale of disease burden (188 million cases, 600,000 deaths), the failure of antibiotics due to AMR, and clear technical feasibility. Multiple vaccine candidates are in clinical development: live attenuated vaccines; conjugate vaccines (S. sonnei and S. flexneri O-antigen conjugates — the most advanced candidates); subunit vaccines; outer membrane vesicle vaccines. Phase 3 trials are expected in the coming years.

How does GMJ News cover shigellosis?

GMJ News covers WHO shigellosis burden data, AMR resistance cascade, azithromycin treatment guidance, S. dysenteriae epidemic history, HUS complication, and vaccine development pipeline. Shigellosis — both a childhood diarrheal killer in LMICs and an increasing MSM concern in HICs — is directly relevant to PHIG's infectious disease programme and Georgia's antimicrobial stewardship agenda.

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Shigellosis (Bacillary Dysentery)

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

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Shigellosis — caused by Shigella species transmitted by a remarkably low infectious dose (as few as 10 organisms) via the fecal-oral route — causes approximately 188 million episodes and 600,000 deaths per year globally, predominantly in children under 5 in LMICs, producing a characteristic syndrome of profuse bloody diarrhoea, painful abdominal cramps and fever that constitutes the clinical picture of bacillary dysentery (WHO). Shigellosis faces a severe antimicrobial resistance crisis — with resistance to ampicillin, trimethoprim-sulfamethoxazole and increasingly to fluoroquinolones and azithromycin — making treatment more difficult and prompting WHO to prioritise Shigella as a high-priority pathogen for vaccine development.

Key messages

188M cases — 600K deaths — AMR crisis

188 million episodes and 600,000 deaths per year — overwhelmingly in children under 5 in LMICs. Shigella faces a severe AMR crisis with resistance to ampicillin, TMP-SMX and increasingly fluoroquinolones (WHO).

Extremely low infectious dose — 10 organisms

Shigella is one of the most infectious bacteria known — as few as 10-100 organisms cause infection, enabling rapid person-to-person spread and large outbreaks from minimal contamination.

Bloody diarrhoea — the clinical hallmark

Shigellosis causes acute bloody diarrhoea (dysentery), painful tenesmus, abdominal cramps and fever. The blood and mucus result from Shigella invading and destroying the colonic epithelium. HUS (from Stx toxin of S. dysenteriae type 1) is a rare but severe complication.

Shigella vaccine — WHO priority

WHO has identified Shigella as a high-priority target for new vaccine development — given the scale of disease burden, the AMR crisis limiting antibiotic options, and the feasibility of vaccination. Multiple candidates are in Phase 2-3 trials.

Children most affected — malnutrition worsens outcome

Shigellosis is particularly devastating in children already malnourished — malnutrition impairs gut barrier function and immunity, allowing more severe invasive disease. Repeated Shigella episodes contribute to growth stunting.

S. dysenteriae type 1 — epidemic potential

Shigella dysenteriae serotype 1 (Sd1) — producing Shiga toxin (Stx) — causes the most severe dysentery and has caused devastating epidemics in Central Africa and Asia. It can cause haemolytic uraemic syndrome (HUS) similar to STEC.

Key statistics

188M

shigellosis episodes/year globally

WHO

600K

shigellosis deaths/year (predominantly children <5)

WHO

10-100

organisms sufficient to cause infection (extremely low ID50)

WHO

bacterial cause of diarrhoeal deaths globally (after E. coli)

GBD

Rising

fluoroquinolone and azithromycin resistance globally

WHO GASP

S. sonnei

most common globally in HICs (less severe); S. flexneri in LMICs

WHO

Shigella species — relative frequency and typical disease severity

Source: WHO. S. flexneri dominates in LMICs; S. sonnei in HICs. S. dysenteriae type 1 causes epidemics.

Glossary of key terms

Dysentery
WHODiarrhoea containing blood and mucus — resulting from mucosal invasion and ulceration of the large intestine. Shigella causes bacillary dysentery (bacterial); Entamoeba histolytica causes amoebic dysentery (parasitic). Clinically: small-volume frequent bloody stools, severe tenesmus (painful sensation of incomplete evacuation), fever.

Shiga toxin (Stx)
WHOA potent cytotoxin produced by Shigella dysenteriae serotype 1 (and STEC E. coli O157:H7). Stx inhibits protein synthesis in endothelial cells — causing haemolytic uraemic syndrome (HUS): microangiopathic haemolytic anaemia + thrombocytopenia + acute kidney failure. Antibiotics may increase Stx release in STEC HUS.

Azithromycin for shigellosis
WHO/WHO EMLAzithromycin (1g single dose or 500mg × 3 days) is increasingly the treatment of choice for MDR shigellosis — particularly ESBL-producing strains resistant to fluoroquinolones. However, azithromycin resistance in Shigella is increasing globally. WHO recommends guided treatment based on local susceptibility patterns.

S. dysenteriae type 1 (Sd1)
WHOThe most virulent Shigella — produces Shiga toxin (Stx), causing severe haemorrhagic dysentery with high mortality and HUS risk. Has caused devastating epidemics: Central Africa 1969-1979; Bangladesh 1970s; Central Africa and Great Lakes region in refugee camps (1994 post-Rwanda genocide).

Reactive arthritis
WHO/RheumatologyA sterile joint inflammation occurring 1-4 weeks after Shigella (and other enteric/STI) infections — previously called Reiter's syndrome. Typically asymmetric oligoarthritis of lower limbs; may be associated with uveitis and urethritis (the classic Reiter's triad). More common in HLA-B27-positive individuals.

Shigella AMR cascade
WHO/GASPShigella has progressively developed resistance to each antibiotic introduced as first-line treatment: ampicillin (widespread resistance); TMP-SMX (widespread resistance); fluoroquinolones (ciprofloxacin resistance >50% in many settings); azithromycin (rising resistance globally). ESBL-producing Shigella (resistant to all cephalosporins) is increasingly documented.

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Shigellosis (Bacillary Dysentery)

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