Why Shigella? One reason is that few bacteria are needed for a person to become ill. Another reason is that the Shigella bacteria are present in the diarrheal stools of infected persons while they are sick and for up to two weeks after they’ve been sick. Most Shigella infections are the result of the bacterium passing from stools or soiled fingers of one person to the mouth of another person because the person handling the food didn’t wash hands with soap after using the bathroom. Publicity about handwashing exists because Shigella bacteria is estimated to cause 450,000 cases of gastroenteritis each year (infections usually result in acute diarrhea), mostly among children under the age of 5. Raw vegetables can become contaminated if they are harvested from a field with sewage in it. Flies can breed in infected feces and then contaminate food as they land on it. Water may become contaminated with Shigella bacteria if sewage or fecal matter runs into it.
During the past two decades, numerous outbreaks of Shigella sonnei have been associated with day-care centers. This makes sense as toddlers aren’t always fully toilet-trained, and their family members and playmates are put at risk of infection. This is also a concern as children under the age of 9 don’t have the immune system development to fight infections easily, so they are harder hit and at greater risk of complications.