Read condition-specific symptoms and clinical context for Shigella flexneri. A dysentery bacterium that needs only a tiny dose; the leading Shigella species in lower-income settings.
S. flexneri is one of four Shigella species and, PHAC states, the leading cause of shigellosis in developing countries, while S. sonnei is the most common species in developed countries. Infection can follow ingestion of only 10 to 200 organisms, and CDC notes that swallowing just a small amount can make someone sick. Illness is usually a self-limited diarrheal or dysenteric episode. Because CDC’s public pages and the US estimates below describe Shigella as a genus, those numbers are labelled genus-level rather than specific to this species.
CDC states that symptoms usually start 1 to 2 days after infection and last 7 days. PHAC gives clinical onset within 12 hours to 3 days and describes infections as usually self-limiting, resolving 5 to 7 days after onset.
Possible symptoms: Diarrhea that can be bloody or prolonged; Fever; Stomach pain; Feeling the need to pass stool even when the bowels are empty.
Bloody or prolonged diarrhea needs medical assessment, and testing can identify the species and check for antimicrobial resistance. These symptoms are listed by CDC for Shigella infection generally rather than for S. flexneri alone.
Carriage without illness is described as rare but can last for months.
PHAC states that although rare, asymptomatic carriers can spread the infection for some months. None of the symptoms listed above apply to this state, and carriage is not shigellosis.
Because the infectious dose is very low, hygiene measures matter even without symptoms. Laboratory testing distinguishes carriage from illness.
Source check: 2026-09-19. Educational content; independent scientific review remains pending.