A small outbreak of listeriosis associated with smoked mussels.
Two perinatal listeriosis cases in Auckland, New Zealand, which were diagnosed during November and December 1992 gave histories of consuming Brand X smoked mussels. Listeria monocytogenes was isolated from an unopened packet of mussels collected from the refrigerator of one of the cases. Cultures of L. monocytogenes from the 2 patients were indistinguishable from those recovered from the mussels by serogrouping and DNA macrorestriction analysis using pulsed-field gel electrophoresis (PFGE). PFGE analysis of isolates of an additional 15 clinical cases caused by L. monocytogenes serogroup 1/2 which occurred in New Zealand during 1991 and 1992, revealed 2 more isolates with indistinguishable PFGE patterns. PFGE analysis of a further 222 L. monocytogenes serogroup 1/2 isolated in New Zealand from food and the environment did not reveal any more cultures with the Brand X PFGE type. A combination of serotyping, phage typing, DNA restriction fragment length polymorphism analysis (RFLP), cadmium and arsenic sensitivity testing, and PFGE analysis was used to subtype 38 isolates of L. monocytogenes. The isolates comprised: (a) the isolates from 4 patients; (b) 26 isolates from 15 packets of Brand X mussel products from retail sale, the processing factory, and the refrigerator of one of the patients; (c) 7 isolates from environmental swabs taken in the processing factory; and (d) an isolate from Brand X mussel product from a wholesaler in the UK. The isolates from 3 of the clinical cases, 26 of the products and 4 from the factory environment were indistinguishable using all the subtyping systems.