Group A, Shigella dysenteriae, Group B, Shigella flexneri, Group C, Shigella boydii, and Group D, Shigella sonnei, which includes only one serotype. Shigella sonnei accounts for most cases of dysentery in the developed world.
Little is known about Shigella and its ability to form and survive in biofilms, which suggests the need for further research. Drinking water treatment that includes disinfection has been shown to be sufficient to remove Shigella. However, waterborne outbreaks have generally resulted from inadequate treatment.