Determining that Shigella is the cause of the illness depends on laboratory tests that identify the bacteria in the stools of infected persons. These tests are sometimes not performed unless the laboratory is instructed specifically to look for the organism. The laboratory also can do special tests to tell which type of Shigella the person has and which antibiotics, if any, would be best to treat it. Because many milder cases are not diagnosed or reported, the actual number of infections may be 20 times greater. Shigellosis is particularly common and causes recurrent problems in settings where hygiene is poor and can sometimes sweep through entire communities.
Shigellosis is more common in summer than winter.
Children, especially toddlers from 2 to 4 years of age, are the most likely to get shigellosis. Many cases are related to the spread of illness in child care settings and many more are the result of the spread of the illness in families with small children. In the developing world, shigellosis is far more common and is present in most communities most of the time. Shigellosis can usually be treated with antibiotics. Appropriate treatment kills the Shigella bacteria that might be present in a patient's stools and shortens the illness.