Which species of Shigella is most commonly associated with diarrheal disease in the United States?

• A. S. dysenteriae
• B. S. flexneri
• C. S. boydii
• D. S. sonnei

Answer: (D)

The species of Shigella most commonly associated with diarrheal disease in the United States is Shigella sonnei. This organism is responsible for the majority of shigellosis cases reported in the country. S. sonnei typically leads to a milder form of the disease compared to the other species in the genus, making it prevalent in both children and adults. Its transmission occurs primarily through the fecal-oral route, often in settings such as daycares or crowded communities, contributing to its common occurrence in outbreaks.

In contrast, S. dysenteriae, while causing severe disease, is less frequently isolated in the U.S. S. flexneri is also implicated in shigellosis but is more common in developing countries. S. boydii is the least frequently encountered species among the Shigella group in the United States, with its presence being quite rare. This context highlights why S. sonnei stands out as the most prevalent species linked to diarrheal disease in this region.