Illness outbreak associated with Escherichia coli O157 : H7 in Genoa salami

Background: An outbreak of Escherichia coli O157:H7 infection was identifie d in the spring of 1998, with a 7-fold increase in the number of laboratory -confirmed E. coli O157:H7 cases in southern Ontario. This prompted an inte nsive investigation by local, provincial and federal public health official s. Methods: Case interviews of 25 people from southern Ontario were conducted using a broad food history and environmental exposure survey. Laboratory in vestigations involved both case and food sampling. Specimens of foods sold locally and reportedly consumed by those affected were tested. Common suppl iers of suspected foods were identified by cross-referencing suppliers' lis ts with stores frequented by those who fell ill. A case-control study invol ving 25 cases and 49 age-matched controls was conducted. This was followed by a comprehensive environmental investigation of the meat processing plant identified as the source of the E. coil. Results: Thirty-nine outbreak-related cases occurred between April 3 and Ju ne 2, 1998. Of the 36 case specimens tested all were positive for E. coil O 157:H7. The case-control study identified Genoa salami as the most probable (odds ratio 8 [confidence interval 2-35]) source of the outbreak. Samples of Genoa salami produced by the most commonly identified supplier later tes ted positive for E. coli O157:H7, and the pathogen matched the same pulsed- field gel electrophoresis pattern and phage type of the case specimens. Interpretation: Our investigation, which led to a national recall of the br and of dry fermented Genoa salami identified as the source of the outbreak, supports an adherence to stringent manufacturing requirements for fermente d meat products. A review of the Canadian standards for fermented meat proc essing and the effectiveness of their implementation is warranted.