A prolonged outbreak of Shigella sonnei infections in traditionally observant Jewish communities in North America caused by a molecularly distinct bacterial subtype.

During 1994-1996, Shigella sonnei outbreaks occurred in 8 North American traditionally observant Jewish communities. These communities remain relatively separate from neighboring populations while maintaining close contact by travel with coreligionists in other cities. Epidemiologic investigations suggested community-to-community transmission via travel. Outbreak-related and control isolates of S. sonnei from each city were subtyped by pulsed-field gel electrophoresis (PFGE) to confirm an epidemiologic linkage between outbreaks. Forty-three (94%) of 46 outbreak-related isolates had closely related PFGE patterns, constituting a single subtype; 33 (94%) of 35 control isolates demonstrated unrelated PFGE patterns. Several patterns differing by < or = 3 bands were identified within the outbreak subtype; one of these accounted for 65% of outbreak isolates. Hence, a single subtype of S. sonnei caused an international outbreak involving 8 traditionally observant Jewish communities, but not neighboring populations, over a 2-year period, suggesting sustained propagation of the epidemic strain between communities.