Cause
Shigellosis is caused by Shigella bacteria. Four main types of Shigella cause infection: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. S. sonnei is the most common type of Shigella in developed countries, including the United States. Outbreaks of shigellosis frequently occur in tropical or temperate climates, especially in areas with severe crowding or poor hygiene that sometimes occur in daycare and institutional settings.