A retrospective analysis of Salmonella serovars isolated from pigs in Great Britain between 1994 and 2010.

A retrospective study analysing Salmonella serovars and antimicrobial resistance data from pigs in Great Britain between 1994 and 2010 was performed. Data were obtained through scanning surveillance and compared with prevalence data from other livestock species as well as human data. During the study period, two serovars, S. Typhimurium and S. Derby, predominated in British pigs. The total number of Salmonella incidents has decreased steadily over the study period, from 360 incidents per year in 1994 to 172 incidents in 2010. S. Typhimurium has been the most common serovar every year, but the relative percentage went down over the past few years. During the same time period, monophasic strains of S. Typhimurium have increased in numbers and were accounting for as much as 25% of incidents in 2010, representing the second most common serovar in British pigs in 2010. Antimicrobial resistance data from S. Typhimurium isolates show that the percentage of isolates which are resistant to six or more antimicrobials has increased from 27.2% in 1994 to 58.3% in 2010 and that the percentage of isolates fully sensitive to the panel of antimicrobials tested was only 3.3% in 2010. S. Typhimurium isolates belonged mainly to phagetypes DT193 and U288 in 2010, and an increase can be seen in the number of isolates belonging to phage type DT193. DT104, which was the predominant phagetype during the 1990s, has gone down considerably and represented less than 5% of all S. Typhimurium isolates in 2010. Monophasic strains of S. Typhimurium belonged mainly to phagetype 193 with less than 20% belonging to phagetype 120. The overall trend shows that the number of Salmonella incidents reported from British pigs has gone down considerably over the 17-year study period, but that the relative percentage of monophasic strains of S. Typhimurium has increased significantly. This trend seems to be in line with observations from other European countries, where an increase of this serovar can be seen both in livestock and in human patients. The increasing percentage of Salmonella-isolates which show multi-resistance is a matter of concern and has to be monitored carefully in order to assess any potential risks this may pose to human patients.