CHARACTERIZATION OF ENDEMIC STRAINS OF SHIGELLA-SONNEI BY USE OF PLASMID DNA ANALYSIS AND PULSED-FIELD GEL-ELECTROPHORESIS TO DETECT PATTERNS OF TRANSMISSION

Shigellosis is hyperendemic in Utah. Most isolates are Shigella sonnei , making it difficult to identify epidemiologic clustering. To better define transmission, molecular markers and epidemiologic data were exa mined for 90 cases, Plasmid analysis and pulsed-field gel electrophore sis (PFGE) of the S. sonnei isolates identified 11 and 4 patterns, res pectively. Plasmid pattern I infections occurred in 8 day care centers over a 6-month period, suggesting spread between centers. Plasmid pat tern III was isolated from children at 3 additional centers and patter n IV was associated with another day care center, suggesting different outbreaks. By PFGE, plasmid groups I and XI appeared identical, as we re plasmid groups II and V; plasmid group X had a unique pattern, Plas mid groups III, IV, and VII-IX were closely related PFGE subtypes. Bot h plasmid analysis and PFGE allow better characterization of S. sonnei transmission patterns of ''endemic'' strains and could lead to improv ed control measures.