SMOKED MUSSELSInvestigators in New Zealand linked three cases that occurred from October to December 1992 to consumption of contaminated smoked mussels [37]. Initially, two perinatal cases caused by serotype 1/2a were detected. A food exposure history indicating consumption of the same brand of mussels prior to development of listeriosis prompted investigators to analyze all 1991 and 1992 serotype1/2a clinical isolates by PFGE. Two additional patient isolates, along with L. monocytogenes isolates from an unopened package of mussels obtained from a patient’s refrigerator, were indistinguishableby PFGE. One patient with illness in October 1992 reported consumption of mussels, but the fourth patient, with illness in May 1991, did not. Isolates from three patients reporting mussel consumption and the mussel isolates were indistinguishable by phage typing, sensitivity to arsenic and cadmium, and restriction fragment length polymorphism (RFLP). The fourth patient’s isolate was untypable via phage typing. This is an oft-encountered caveat of this subtyping method, and likely means that the isolate was of a type not represented in the phage set [105]. These laboratory findings highlight the higher discriminatory power offered by characterization with more than one typing method when feasible.
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