Definition. Shigella infection (shigellosis) is an intestinal disease caused by a family of bacteria known as shigella. The main sign of shigella infection is diarrhea, which often is bloody.Shigella can be passed through direct contact with the bacteria in the stool.For example, this can happen in a child care setting when staff members don't wash their hands well enough after changing diapers or helping toddlers with toilet training.he main sign of shigella infection is diarrhea, which often is bloody. Shigella can be passed through direct contact with the bacteria in the stool. For example, this can happen in a child care setting when staff members don't wash their hands well enough after changing diapers or helping toddlers with toilet training.