Risk factors for contamination of smoked salmon with Listeria monocytogenes during processing

Forty smoked salmon processing plants were examined for the occurrence of Listeria monocytogenes and other Listeria spp. in the smoked salmon and the drains. L. monocytogenes was detected in smoked salmon from 13 (33%) and in the drains samples from 25 (63%) of the plants. Other Listeria spp. were found in smoked salmon samples from 16 (40%) and in the drains of 30 (75%) of the plants. Multivariate analyses of data on hygiene, management, production facilities of the plants and bacteriological results showed that job rotation was the strongest expressed risk factor for isolation of L. monocytogenes from the smoked salmon (hazard ratio, HR = 11.0, p = 0.002). Well-maintained facilities (HR = 0.31, p = 0.064) and use of vats for salting of the fillets (HR = 0.33, p = 0.109), showed a preventive effect. L. monocytogenes in the drains was found to be a sensitive predictor for the presence of L. monocytogenes in the smoked salmon. In general, detection of other Listeria spp. in the smoked salmon or the drains could not be demonstrated to have any association with detection of L. monocytogenes.