The incubation period is 1 to 4 days. In younger children, onset is sudden, with fever, irritability or drowsiness, anorexia, nausea or vomiting, diarrhea, abdominal pain and distention and tenesmus. Within 3 days, blood, pus and mucus appear on the stools. Though adults may present without fever, with nonbloody and nonmucoid diarrhea, and with little or no tenesmus, the onset of illness may be characterized by epidoses of griping abdominal pain, urgency to defecate, and passage of formed feces initially. These periods recur with increasing severity and frequency.
Diarrhea becomes marked, with soft or liquid stools containing mucus, pus, and often blood.
Rectal prolapse and consequent fecal incontinence may result from severe tenesmus. Significant dehydration and electrolyte loss with circulatory collapse and death is limited mainly to infants Secondary bacterial infections may occur, especially in debilitated and dehydrated patients. The bacillus is found in the stools. Diagnosis is facilitated by a high index of suspicion during outbreaks and in endemic areas. The most common form, watery diarrhea, is indistinguishable from other bacterial, viral and protozoan infections that induce secretory activity of intestinal epithelial cells.