In Summary
- Analysis of risk factors for isolating L. monocytogenes from smoked fish found that the biggest risk came from rotation of plant employees from one processing task to the other.
- Replacement of gloves when handling raw fish has been found to reduce cross contamination between L. monocytogenes positive and negative fish.
- A study also found that processing plant employees had more L. monocytogenes on their hands than non-plant employees.
- Effective and frequent hand washing practices are recommended for plant employees, to reduce risk.
Multivariate analyses of relationships between microbiological test results, operating hygiene, management practices and the state of repair of the production facilities showed that job rotation (employees periodically changing their processing task to prevent boredom) was the strongest expressed risk factor for isolation of L. monocytogenes from the smoked salmon (Rørvik et al. 1997).
Two different studies (Autio et al, 1999; Dauphin et al, 2001) considered that plant employees and their equipment (especially ineffectively-cleaned aprons and gloves), could be minor vectors of product contamination.
In addition, a mathematical model of cross contamination within a fish processing plant was developed and its predictions validated against real world observations (Ivanek et al, 2004). The main finding of the study was that if L. monocytogenes was present in batches of raw fish, employee gloves were more likely to become contaminated towards the end of a processing shift. The simple intervention of changing gloves with greater frequency (e. g. halfway through a shift) would significantly reduce the contamination of L. monocytogenes-free fish from employees’ gloves (Ivanek et al, 2004).
More generally, the prevalence of carriage of Listeria spp. on the hands of food workers was investigated by Kerr et al. (1993). The hands of almost 100 workers engaged in food processing and retailing were assessed for contamination by L. monocytogenes and Listeria spp. Just over 10% of the samples collected were from fish processing or retailing establishments. The hands of 75 clerical workers were also tested for control purposes. Overall, 12 (12%) of food handlers had Listeria spp. on their hands and 7 (7%) harboured L. monocytogenes. None of the clerical control group tested positive for Listeria spp. A conclusion of the study was that food handlers were more likely than general workers to have their hands contaminated by L. monocytogenes.
The Kerr (1993) study also assessed the impact of various hand washing practices. Where Listeria contamination on hands was low (<20 cfu per hand), hand washing using soap effectively eliminated the organisms. However, hand washing was not effective at removing Listeria when larger numbers were present. Furthermore, if hand washing was not carried out effectively there was a chance that washing could actually contaminate worker’s hands. Kerr et al. (1993) observed two instances where there was no contamination of worker’s hands before washing, but there were post-wash isolations of Listeria. Kerr and colleagues (1993) concluded that poor washing appeared to have caused contamination of subjects' hands. It is therefore important that hands are washed effectively and frequently, and if gloves are used they are changed regularly.
