Family outbreak of dysentery caused by a rhamnose non-fermenting, ONPG-negative strain of Shigella sonnei phage type 6.

Three members of a Scottish family, with no history of foreign travel but who had recently visited Bristol, were infected by a strain of Shigella sonnei of phage type 6 (PT 6) that did not ferment rhamnose and was negative for o-nitrophenyl-beta-D-galactopyranoside (ONPG). The incident exposed limitations associated with commercial systems for the identification of strains of S. sonnei with atypical biochemical properties.