The source of infection is the excreta of infected individuals or convalescent carriers. Water-borne disease is unusual. Flies serve as mechanical vectors.
Epidemics occur most frequently in overcrowded populations with inadequate sanitation.
Convalescents and subclinical carriers may be significant sources of infection. Infection imparts little or not immunity, since reinfection with the same strain is possible. 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.