Cluster of Cases of Salmonella enterica Serotype Rissen Infection in a GeneralHospital, Italy, 2007

In 2007, three strains of Salmonella enterica serotype Rissen (S. Rissen)were isolated in the laboratory of diagnostic microbiology of the GeneralHospital of Prato, Tuscany, Italy, over a 1 month and half interval of time. The first isolate was recovered on January 26 from an outpatient with enteritis.Then, two strains were isolated on February 16 and March 11 respectively, fromcentral venous catheters of patients who were being hospitalized in twodepartments of the Hospital. An epidemiologically linked cluster of cases ofsalmonellosis was suspected. The three strains were submitted to singleenzyme-amplified fragment length polymorphism (SE-AFLP) and XbaI macrorestrictionand pulsed-field gel electrophoresis (PFGE) that yielded undistinguishableprofiles. Epidemiological investigations failed to identify a common source ofinfection within the Hospital. Moreover, the third patient had been exclusivelytotal parenteral nutrition fed since his admission with a stomach cancerdiagnosis. The first patient had a community-acquired infection, but the sourceof her illness was uncertain. Twenty-five further isolates identified in theyears 2004-2007 in the same geographical area showed distinctly different PFGEand SE-AFLP patterns. The three patients seemed to represent a cluster ofepidemiologically unrelated cases caused by a previously never recognized S.Rissen strain. Rapid subtyping of isolates is essential in the earlyinvestigation of potential outbreaks, but synthesis of conventional and molecularepidemiological investigation and availability of surveillance data is oftencritical to prevent the initiation of time-consuming, expensive and ineffectivefurther investigations and control interventions.