Scanning electron micrograph (SEM) of Shigella sonnei. Shigella sonnei causes approximately 10,000 cases of gastroenteritis each year in the United States. Infections occur predominately among young children and usually are associated with poor hygienic conditions in child-care settings. Although commonly regarded as waterborne, shigellosis is also a foodborne disease, restricted primarily to higher primates, including humans. (Microscope magnification: 23,000x. Image width: 5.56 micrometers. Bar: 1 micrometer.).