EFSA explains the background to this report, which is that Salmonella is a major cause of food-borne illness in humans. Farm animals and foods of animal origin are important sources of human Salmonella infections. In order to reduce the incidence of human salmonellosis in the European Union, it says, Community legislation foresees the setting of Salmonella reduction targets for food/animal populations, including breeding pigs.

The Authority continues that, to underpin such targets, a series of baseline surveys have been conducted to ascertain the occurrence prior to the implementation of such Community legislation, explains EFSA. This fifth European Union-wide baseline survey was carried out at farm level to determine the prevalence of Salmonella in pig breeding holdings. The herds were randomly selected from holdings constituting at least 80 per cent of the breeding pig population in a Member State.

Procedure Used for Sampling

Sampling took place between January 2008 and December 2008. A total of 1,609 holdings housing and selling mainly breeding pigs (sows or boars of at least six months of age kept for breeding purposes) ('breeding holdings') and 3,508 holdings housing breeding pigs and selling mainly pigs for fattening or slaughter ('production holdings') from 24 European Union Member States, plus Norway and Switzerland were included in the survey.

In each selected breeding and production holding, fresh voided pooled faecal samples were collected from 10 randomly chosen pens, yards or groups of breeding pigs over six months of age, representing the different stages of production of the breeding herd (maiden gilts, pregnant pigs, farrowing and lactating pigs, pigs in the service area, or mixed). The pooled samples from each holding were tested for the presence of Salmonella and the isolates were serotyped. The country level and European Union level prevalence presented in the report are apparent prevalence, meaning that the prevalence estimates do not account for imperfect sampling and test characteristics.

A total of more than 51,000 samples were taken and analysed as part of this study.

Results

Prevalence of Salmonella

Breeding holdings
The overall European Union prevalence of Salmonella-positive holdings with breeding pigs was 31.8 per cent and all but one participating Member State detected Salmonella in at least one holding, according to the report.

Twenty of the 24 Member States isolated Salmonella in breeding holdings and at European Union level, 28.7 per cent of the holdings was estimated to be positive for Salmonella. This prevalence varied from zero to 64.0 per cent among the Member States.

The estimated European Union prevalence of breeding holdings positive to Salmonella Typhimurium and to Salmonella Derby was 7.8 per cent and 8.9 per cent, respectively.

Production holdings
Twenty-one of the 24 Member States isolated Salmonella in production holdings and at the European Union level 33.3 per cent of the production holdings was estimated to be positive for Salmonella. This prevalence varied from zero to 55.7 per cent among the Member States.

The estimated European Union prevalence of production holdings positive for S. Typhimurium and S. Derby was 6.6 per cent and 9.0 per cent, respectively.

For the two non-Member States, Switzerland detected Salmonella in both breeding and production holdings while Norway did not detect any Salmonella in its surveyed holdings.

Types of Salmonella found

* "S. Typhimurium is commonly reported in human salmonellosis cases in the EU, whereas the other serovars generally constitute a minor proportion of human infections."

The number of different Salmonella serovars isolated in breeding holdings and production holdings across the European Union was 54 and 88, respectively.

S. Derby was the most frequently isolated serovar in both breeding and production holdings, detected in 29.6 per cent and 28.5 per cent of the Salmonella-positive holdings, respectively.

The next most commonly isolated serovar was S. Typhimurium accounting for 25.4 per cent and 20.1 per cent of Salmonella-positive breeding holdings and production holdings, respectively. Of the serovars, S. Typhimurium is also commonly reported in human salmonellosis cases in the EU, whereas the other serovars generally constitute a minor proportion of human infections.

These serovars were also commonly found in the EU-wide baseline survey of fattening pigs at slaughter in 2006-2007.

The next most frequently reported serovars were S. London, S. Infantis and S. Rissen, both in breeding and production holdings and each accounted for approximately seven per cent of the positive holdings, in each type of holding. Also Salmonella isolates with the incomplete antigenic formula 4,[5],12:i:-, which are likely to be related to the recent emergence of monophasic S. Typhimurium, were reported by several Member States.

* "S. Typhimurium accounted for 25.4 per cent and 20.1 per cent of Salmonella-positive breeding holdings and production holdings, respectively"

Conclusions of the Survey

This baseline survey was the first survey on Salmonella in holdings with breeding pigs in the EU. EFSA reports that it provides comparable estimates of the prevalence of Salmonella-positive holdings with breeding pigs for the EU MSs and provides a description of the occurrence of Salmonella across the EU. These baseline prevalence figures may be used in the future to follow trends and to evaluate the impact of control programmes.

The survey demonstrated that Salmonella is very common in holdings with breeding pigs, either breeding or production holdings, and widely distributed in the EU. All but one of the 24 participating MSs detected Salmonella in at least one of their holdings.

EFSA found that 20 of the 24 Member States isolated Salmonella in breeding holdings. At EU level, approximately one in three breeding holdings (28.7 per cent) was estimated to be positive for Salmonella. The prevalence of Salmonella-positive breeding holdings varied widely among the Member States from zero to 64.0 per cent. The estimated EU prevalence of breeding holdings specifically positive for S. Typhimurium and S. Derby was 7.8 per cent and 8.9 per cent, respectively.

Furthermore, 21 of the 24 Member States isolated Salmonella in production holdings. At EU level, one-third of the production holdings (33.3 per cent) were estimated to be positive for Salmonella. The prevalence of Salmonella-positive production holdings also varied widely among the MSs from zero to 55.7 per cent. The estimated EU prevalence of production holdings specifically positive for S. Typhimurium and S. Derby was 6.6 per cent and 9.0 per cent, respectively.

The number of different Salmonella serovars isolated in breeding holdings and production holdings across the European Union was 54 and 88, respectively. S. Derby was the most frequently isolated serovar in both breeding and production holdings, detected in 29.6 per cent and 28.5 per cent of the Salmonella-positive holdings, respectively.

The second most commonly isolated serovar was S. Typhimurium accounting for 25.4 per cent and 20.1 per cent of Salmonella-positive breeding holdings and production holdings, respectively. The next most frequently reported serovars were S. London, S. Infantis and S. Rissen both in breeding and production holdings and each accounted for approximately 7% of the positive holdings, in each type of holding.

Salmonella isolates with the incomplete antigenic formula 4,[5],12:i:- were found in several MSs. These are likely to be related to the recent emergence of monophasic S. Typhimurium, which has been found predominantly in pigs and humans. EFSA explains that the main public health importance of Salmonella in breeding pigs is the potential dissemination of the bacteria to rearing and fattening pigs. This may lead to Salmonella contamination of pig meat and consequently to human infection. The results of this survey will support the risk managers in setting targets for the reduction of the prevalence of Salmonella infection in holdings with breeding pigs in the EU, adds EFSA.

EFSA's Recommendations

Based on this baseline study, EFSA firstly recommends detailed research on the epidemiology and, in particular, effective surveillance methods (i.e. monitoring and control) of Salmonella in primary breeding pigs as the information this area is sparse and studies would therefore be welcome.

It adds that knowledge of the public health impact of the consumption of meat and offal from culled sows is lacking, and that studies on this issue would be desirable.

And finally, EFSA recommends that molecular typing studies on the stored isolates of monophasic Salmonella strains from this survey, as well as epidemiological studies, are needed to confirm that these strains are part of the increasing trend of monophasic S. Typhimurium strains and to explore factors that are driving this emergence.

Further Reading

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Further Reading

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February 2010