Submitted to: Epidemic Intelligence Service Conference
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2011
Publication Date: 4/15/2011
Citation: Farag, N., Gaul, L., Silk, B.J., Trees, E., Kingsley, M., Graves, L., Ward, T.J. 2011. Outbreak of Nosocomial Listeriosis — Texas, 2010. Epidemic Intelligence Service Conference. Interpretive Summary:
Technical Abstract: Background: Invasive listeriosis is a potentially fatal foodborne disease caused by Listeria monocytogenes. In February 2010, a listeriosis cluster was identified in Texas. We investigated to confirm the outbreak, identify the source, and prevent additional infections. Methods: All clinical isolates of L. monocytogenes with similar pulsed-field gel electrophoresis (PFGE) subtypes were identified within the PulseNet surveillance system. We used multilocus variable-number tandem-repeats analysis (MLVA) and multilocus genotyping (MLGT) to confirm molecular subtype relatedness, interviewed patients regarding food consumption, and reviewed their medical charts. Environmental and food samples were cultured. Results: We identified 10 cases with highly related PFGE subtypes with patients' illness onsets during February–August 2010. Nine of 10 cases were among patients from 1 of 4 hospitals before illness onset, with 6 having been at Hospital A. A tenth patient had eaten at 3 hospital cafeterias. Mean patient age was 77 years (range: 56–93); case-fatality ratio was 50%. Of 198 environmental and 30 food samples collected, L. monocytogenes was detected in chicken salad and prepackaged diced celery only. Traceback investigation identified a celery processing plant from which L. monocytogenes was isolated from environmental and product samples. Subtyping of isolates identified indistinguishable PFGE patterns to clinical, celery, and chicken salad isolates from Hospital A and clinical isolates from the other hospitals. Clinical, environmental, and product isolates were indistinguishable by MLVA and MLGT. Conclusions: Prepackaged diced celery was recalled and plant operations suspended. This investigation directly implicated celery for the first time as a vehicle in a listeriosis outbreak. Given the high fatality, produce should be recognized as a potential source of L. monocytogene. Risk mitigation strategies should be considered for highly vulnerable populations.