Outbreak of Shewanella algae and Shewanella putrefaciens infections caused by a shared measuring cup in a general surgery unit in Korea

Abstract

OBJECTIVE: To control an outbreak of Shewanella algae and S. putrefaciens infections by identifying the risk factors for infection and transmission. DESIGN: Matched case-control study. SETTING: A university-affiliated tertiary acute care hospital in Seoul, Republic of Korea, with approximately 1,600 beds. PATIENTS: From June 20, 2003, to January 16, 2004, a total of 31 case patients with Shewanella colonization or infection and 62 control patients were enrolled in the study. INTERVENTIONS: Requirement to use single-use measuring cups and standard precautions (including hand washing before and after patient care and use of gloves). RESULTS: S. algae or S. putrefaciens was isolated from blood, for 9 (29.0%) of 31 patients who acquired one of the organisms; from bile, for 8 (25.8%), and from ascitic fluid, for 8 (25.8%). The attack rate of this outbreak was 5.8% (31 patients infected or colonized, of 534 potentially exposed on ward A) and the pathogenicity of the two species together was 77.4% (24 patients infected, of 31 who acquired the pathogens). The estimated incubation period for Shewanella acquisition was 3-49 days. Using logistic analysis, we identified the following risk factors: presence of external drainage catheters in the hepatobiliary system (odds ratio [OR], 20; P < .001), presence of hepatobiliary disease (OR, 6.4; P < .001), admission to the emergency department of the hospital (OR, 2.9; P = .039), wound classification of "contaminated" or "dirty or infected" (OR, 16.5; P = .012), an American Society of Anesthesiologists score of 3 or higher (OR, 8.0; P = .006), duration of stay in ward A (OR, 1.1; P < .001), and, for women, an age of 60-69 years (OR, 13.3; P = .028). A Shewanella isolate was recovered from the surface of a shared measuring cup, and 12 isolates of S. algae showed the same pulsed-field gel electrophoresis pattern. CONCLUSIONS: This Shewanella outbreak had a single-source origin and spread by contact transmission via a contaminated measuring cup. Shewanella species are emerging as potentially serious human pathogens in hospitals and could be included in hospital infection surveillance systems.