Pathophysiology
S. sonnei (most common in high-income countries), S. flexneri (endemic in low-income), S. dysenteriae (severe, produces Shiga toxin). Invades M cells of the colon, spreads intracellularly via actin polymerisation, and causes inflammatory colitis; Shiga toxin can precipitate haemolytic-uraemic syndrome.
Sources: IDSA Infectious Diarrhoea Guideline (Clin Infect Dis 2017;65:e45); CDC Shigella Fact Sheet (2024); WHO Diarrhoeal Disease Reports
Clinical presentation
1-3 day incubation, initial watery diarrhoea then small-volume bloody, mucoid stools with fever, cramps and tenesmus. Complications: HUS (especially S. dysenteriae), reactive arthritis (HLA-B27), toxic megacolon, seizures in children.
Diagnosis
Stool culture or multiplex PCR; faecal WBCs/lactoferrin positive. Consider extended-spectrum beta-lactamase (ESBL) and fluoroquinolone resistance - rising globally, notably in men who have sex with men.
Management
Oral/IV rehydration. Empiric antibiotics recommended (unlike Salmonella) to shorten illness and reduce transmission: azithromycin adult 500 mg x 3 days, or ceftriaxone for severe/resistant cases. Avoid loperamide.
Prevention
Hand hygiene, safe food and water, exclude infected food handlers/healthcare workers until 2 negative stool cultures. No vaccine currently licensed.
