Differences and similarities among experts' opinions on Salmonella enterica dynamics in swine pre-harvest.

A workshop was conducted to elicit expert opinion on infection status and transmission of salmonella in pigs at the farm of origin, during transport and during lairage. A second objective was to compare opinions regarding risk factors for salmonella introduction and control at the farm level between experts from different countries. Thirty-six experts from 11 countries filled in a paper-and-pencil questionnaire during an international conference. Experts from all countries agreed on the risk of salmonella introduction related to live animals and the importance of general hygiene and all-in/all-out management for salmonella control. However, workshop participants from Denmark put more weight on factors related to feed while experts from USA rated factors related to rodents and people contact higher. The experts believed that 21-33% of pigs coming from a chronically infected farm would be infected with salmonella, but only one-third of the infected pigs would be shedders. Regarding transport and lairage, the US participants believed that contamination was occurring in the majority of pigs regardless of initial infection status and particularly during lairage; in contrast, the Danish experts were more optimistic with respect to the contamination and infection risk. US experts believed that the incidence of salmonella shedding would be high among pigs infected during transport and lairage and that an important proportion of 'carrier' pigs would start shedding. Our results reflect the differences in the level of salmonella infection and implemented control strategies between countries as well as the different philosophies that professionals have. The differences in opinion regarding salmonella dynamics could be due either to true differences in risk as a consequence of distinct management and transport practices in Denmark and USA or to a difference in perception.