In July 2015, Shigella sonnei infections with a specific pulsed-field gel electrophoresis (PFGE) pattern linked to a multistate outbreak were recognized among men who have sex with men (MSM) in the Portland metropolitan area, and an outbreak investigation was initiated. During November 2015, isolates with PFGE patterns indistinguishable from the outbreak strain were identified in cases reported in four women, none of whom had epidemiologic links to other affected persons; however, three reported homelessness. In the ensuing months, additional S. sonnei infections were reported among homeless persons in the Portland area.