[Protracted nosocomial outbreak of Salmonella Enteritidis LT 8/7]

Abstract

Introduction: In spring 2007a cluster of nosocomial salmonellosis cases, culture confirmed for SALMONELLA Enteritidis lysotype (LT) 8/7, occurred in a Wolfsburg hospital. An outbreak investigation was initiated to determine the epidemiology of the outbreak and to identify and control the possible sources.

Methods: A multidisciplinary outbreak team was formed including members from hospital hygiene and local, state and national health and veterinarian authorities. Active surveillance was set up in the hospital to find new cases. A retrospective case control study was conducted to identify possible risk factors for disease. Hospital workers and food samples were tested for the pathogen and positive isolates were typed.

Results: Between calendar weeks 4 and 24 of the year 2007, a total of 28 patients with a median age 66 years had nosocomial salmonellosis culture confirmed for SALMONELLA Enteritidis LT 8/7. In food samples from February, the same Salmonella lysotype was isolated in 4 different food samples. SALMONELLA Enteritidis LT 8/7 was also identified in stool samples from 5 kitchen personnel. The case control study indicated antacida therapy (odds ratio: 5.5, 95 % CI 1.2 - 26.0) as a risk factor for nosocomial salmonellosis among patients. No particular diet was associated with an increased risk of disease.

Discussion: This nosocomial salmonellosis outbreak was characterised by prolonged duration and a low infection rate among patients. The epidemiological investigation suggests that the origin of the outbreak was food that was probably associated with a contamination in the hospital kitchen. Furthermore, kitchen staff could, as carriers, have contributed to a low-level contamination of various foods for a long period. The intermittent occurrence of the cases is best explained by a low level of contaminated food which primarily led to clinical symptoms among especially vulnerable persons (older patients with antacida therapy). Considering the unusual progression of this outbreak, hospitals should initiate an intensive epidemiological and microbiological investigation, even if only few nosocomial salmonellosis cases occur.