On October 20, 2010, the South Carolina Department of Health and Environmental Control and CDC began investigating a cluster of three diarrheal illnesses caused by multidrug-resistant Shigella flexneri 2a. The index case occurred in a girl aged 2 years who experienced the onset of diarrhea on September 25 and was hospitalized the next day because of a seizure and fever. On September 30, her brother, aged 6 years, was hospitalized with vomiting, bloody diarrhea, and hyponatremia. Three days later, her father was hospitalized with vomiting, bloody diarrhea, and hyponatremia.