Shigellosis and Dysentery
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Direct answer
Shigellosis is an invasive bacterial infection of the colon caused by Shigella species, and it is a major cause of bacillary dysentery in children. It produces fever, abdominal cramps and small stools containing blood and mucus, and very few organisms are enough to cause disease. Antibiotic choice must follow local sensitivity, since resistance to ampicillin and cotrimoxazole is common, and complications such as haemolytic uraemic syndrome need early recognition.
What you must remember
- Organism: Shigella is a non-motile, gram-negative bacillus that invades the colonic mucosa, and humans are its only reservoir.
- Species: Shigella sonnei and Shigella flexneri are common in India, while Shigella dysenteriae type 1 produces Shiga toxin and causes the most severe disease.
- Clinical picture: fever, abdominal cramps, tenesmus and frequent small stools with blood and mucus, usually with many polymorphs on stool microscopy.
- Diagnosis: stool culture on selective media is the standard test, and sensitivity testing is needed to guide therapy.
- Antibiotics: ciprofloxacin is the WHO first-line oral drug, with azithromycin or ceftriaxone as second-line options where resistance or severity demands; local sensitivity guides the final choice.
- Avoid: antimotility agents such as loperamide, because they can precipitate toxic megacolon and prolong the infection.
- Complications: haemolytic uraemic syndrome, seizures in young children, rectal prolapse and reactive arthritis.
A graded approach from rehydration to targeted antibiotics
A 3-year-old presents with two days of fever, six bloody stools and tenesmus. Management combines fluid therapy with a targeted antibiotic, and the steps are ordered by urgency. Dehydration and haemolytic uraemic syndrome can both progress quickly, so the child is reassessed at every step.
- Rehydrate first. Start oral rehydration solution, and use intravenous fluids for severe dehydration or shock, following the standard plan for the child's degree of dehydration.
- Recognise severity. Look for high fever, altered sensorium, convulsions and signs of toxicity, since these change the antibiotic choice.
- Send stool culture before antibiotics. Culture confirms the organism and provides the sensitivity profile that decides the drug.
- Choose the antibiotic by sensitivity. Use ciprofloxacin as the WHO first-line drug where the strain is sensitive, and reserve azithromycin or ceftriaxone for resistant strains or severe illness.
- Watch for haemolytic uraemic syndrome. Monitor for pallor, falling platelets, rising creatinine and reduced urine output in the days after the diarrhoeal phase, and continue zinc and feeding throughout.
Where the exam tries to catch you
Shigella questions reward students who link the organism to its toxin and its drug choices.
- Trap: using loperamide to stop bloody diarrhoea Correct: antimotility drugs are contraindicated in dysentery because they can cause toxic megacolon and keep the bacteria in the bowel longer.
- Trap: choosing ampicillin by default Correct: resistance to ampicillin and cotrimoxazole is widespread, so the antibiotic must follow the local sensitivity report.
- Trap: attributing haemolytic uraemic syndrome only to E. coli O157 Correct: Shigella dysenteriae type 1 is also a classic cause, because its Shiga toxin damages the kidney.
Frequently asked questions
Which Shigella species causes the most severe disease and haemolytic uraemic syndrome?
Shigella dysenteriae type 1 causes the most severe disease, because it produces Shiga toxin that can damage the kidney and the brain. It is strongly linked with haemolytic uraemic syndrome, which must be looked for in children with reduced urine output or falling platelets after dysentery.
Why is loperamide avoided in shigellosis?
Loperamide and other antimotility drugs are avoided in shigellosis because they slow intestinal transit and can precipitate toxic megacolon. Keeping the bacteria in the bowel for longer also prolongs the infection, so rehydration and zinc are preferred as supportive care.
Why do children with shigellosis have seizures?
Seizures in shigellosis occur mostly in young children with high fever, and they need prompt treatment of the fever and evaluation for encephalopathy. The mechanism is not fully settled, but fever and toxin-related effects are the usual explanations, so the seizures are managed like other febrile convulsions.
Which antibiotic is the first choice in shigellosis?
WHO guidance names ciprofloxacin as the first-line oral antibiotic for shigellosis, including in children, because resistance varies by region. Azithromycin and ceftriaxone are second-line choices for resistant strains or severe illness, and the local antibiogram guides the final choice.