Classification
Shigella species are classified by four serogroups:
- Serogroup A: S. dysenteriae (12 serotypes)
- Serogroup B: S. flexneri (6 serotypes)
- Serogroup C: S. boydii (18 serotypes)
- Serogroup D: S. sonnei (1 serotype)
Groups A–C are physiologically similar; S. sonnei (group D) can be differentiated on the basis of biochemical metabolism assays. Three Shigella groups are the major disease-causing species: S. flexneri is the most frequently isolated species worldwide, and accounts for 60% of cases in the developing world; S. sonnei causes 77% of cases in the developed world, compared to only 15% of cases in the developing world; and S. dysenteriae is usually the cause of epidemics of dysentery, particularly in confined populations such as refugee camps.
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