Outbreak of Shigella sonnei dysentery on a long stay psychogeriatric ward.

A ward outbreak of diarrhoea associated with Shigella sonnei on a long stay psychogeriatric ward is described. Nine patients and three staff had positive stool cultures for S. sonnei. The source of infection of the index case was not discovered. Environmental factors at ward level which predispose long stay hospitals to such outbreaks are discussed.