Reports of Salmonella in Chickens

At the time of the June 2009 Agricultural Census¹, there were just under 131.2 million chickens in Great Britain, comprising approximately 32 million layers, 91.4 million broilers and 7.8 million breeders. Compared to 137.9 million chickens in 2008, this is a total reduction of approximately 5 per cent.

A reduction in the total numbers of chickens does not necessarily imply a reduction in the number of chicken holdings and/or flocks as it does not take into account a possible change in the average size of farms and/or flocks.

In this chapter, two different systems of reporting are used and therefore the interpretation of the data should be done bearing this in mind.

• Incidents are defined as the first isolation and all subsequent isolations of the same Salmonella serovar or phage type of typable serovars from an animal, group of animals or their environment on a farm within a defined time period (normally 30 days unless it is known that the reports relate to the same group of animals). An incident could therefore theoretically involve more than one flock and/or house sampled at the same time and subsequent crops from the same house or holding if insufficient holding data is available, but this would be a rare occurrence. The first part of this chapter describes incidents and includes samples originating from statutory surveillance, voluntary surveillance, investigations into clinical disease and investigations carried out under the Zoonoses Order.
  
  
• The second part of this chapter describes results derived from the National Control Programmes (NCPs) in Great Britain, i.e. results from statutory surveillance. Results from the NCPs are reported to the European Commission in a way that every flock with a Salmonella - positive result is counted, even in cases when more than one flock on the same premises test positive at the same time or within a short period of time. Numbers of positive flocks reported within the NCP are therefore expected to be higher than the number of reported incidents from statutory Salmonella surveillance. However, some flocks may be positive for more than one serovar, in which case they are still only counted once as positive flocks. This also applies if there is a longer interval between the positive tests. It should also be noted that the poultry industry is currently the only food animal production sector that has structured bacteriological surveillance programmes for Salmonella in place. This routine monitoring would be expected to result in larger numbers of Salmonella isolates than the scanning surveillance of diagnostic submissions that applies to other farm livestock.

Salmonella data from the previous two years (Salmonella in Livestock Production in GB, 2008 and 2009) can be accessed via the VLA web site².

The total number of chicken submissions to VLA/SAC laboratories increased by 66 per cent in 2009 (6,421 submissions) compared to 2008 (3,868 submissions). This is mainly due to a 127 per cent increase in the number of submissions from statutory surveillance (1,972 in 2008 versus 4,480 in 2009). Submission numbers from voluntary surveillance went down by 28 per cent (334 in 2008 versus 241 in 2009). The changes in submission numbers are mostly due to the implementation of the broiler NCP in 2009, which resulted in surveillance samples from the broiler sector being recorded as statutory surveillance rather than voluntary. The number of diagnostic submissions showed a small increase of 8 per cent (1,466 in 2008 versus 1,588 in 2009).

A total of 439 Salmonella incidents were reported in 2009 as shown in Table 6.1. This number includes incidents from statutory surveillance, voluntary surveillance, diagnostic submissions and investigations of clinical disease.

The total number of incidents were distributed among the following groups according to the reason for submission:

• statutory surveillance: 383 (87.2 per cent), (97 in 2008; 38.7 per cent)
• voluntary surveillance: 53 (12.1 per cent), (136 in 2008; 54.2 per cent)
• samples taken under the Zoonoses Order: 1 (0.23 per cent), (15 in 2008; 6 per cent)
• investigations of clinical disease: 2 (0.46 per cent), (2 in 2008; 0.8 per cent)

Compared with 251 reported incidents in 2008, there was an increase of 75 per cent observed in 2009; this is due to an increase in the number of incidents from statutory surveillance (from 97 in 2008 to 383 in 2009), whereas the number of incidents from voluntary surveillance declined from 136 to 53 during the same period.

The incidents originated from the following production types:

• Broiler breeders: 22 (5 per cent), (35 in 2008; 14 per cent)
• Layer breeders: 6 (1.4 per cent), (11 in 2008; 4.4 per cent )
  • Breeders total: 28 (6.4 per cent), (46 in 2008; 18.3 per cent
• Broilers: 274 (62.4 per cent), (75 in 2008; 30 per cent)
• Layers: 131 (29.8 per cent), (129 in 2008; 51.4 per cent)
• Pet chickens: 4 (0.9 per cent), (1 in 2008; 0.4 per cent)
• Unknown type: 2 (0.45 per cent), (0 in 2008; 0.8 per cent)

Between 2008 and 2009, the number of incidents reported from breeding flocks (both broiler breeder and layer breeder flocks) went down by 39.1 per cent (from 46 in 2008 to 28 in 2009), and incidents from breeders accounted for 6.4 per cent of all chicken incidents in 2009 only, compared to 18.3 per cent in 2008. Incident numbers declined at about the same rate in broiler breeders and layer breeders. Although the total number of registered breeding flocks was 5.3 per cent lower in 2009 compared to 2008, breeding flocks have been subject to statutory monitoring throughout this two-year period, thus allowing direct comparison of the incident numbers from 2008 and 2009.

At the same time, the total number of incidents reported from layers remained almost the same (129 incidents in 2008 versus 131 in 2009), but layer incidents accounted for a lower proportion of all chicken incidents in 2009 than in 2008 (29.8 per cent versus 51.4 per cent). As statutory monitoring for layers was only introduced in February 2008, incident numbers from 2008 and 2009 should not be compared directly.

The biggest change between 2008 and 2009 happened in the broiler sector, where the number of incidents more then tripled (75 incidents in 2008 versus 274 incidents in 2009). Therefore, broiler incidents accounted for 62.4 per cent of all incidents in 2009 compared to 30 per cent in 2008.

This increase is likely to be due to the introduction of the National Control Programme for the Control of Salmonella in broilers in 2009.

Thirty-six different serovars of Salmonella enterica subspecies enterica were isolated in 2009, accounting for 416 of the 439 incidents. This compares to 31 different serovars in 2008. Nineteen incidents involved Salmonella enterica strains that were not fully typable to serovar level, three incidents involved Salmonella enterica rough strains and one incident involved Salmonella enterica subspecies diarizonae.

Table 6.2 shows the most common Salmonella serovars in chickens from 2005 to 2008, and data for 2009 are shown in Figure 6.1. Salmonella Kedougou (16.6 per cent), S. Senftenberg (16.4 per cent), S. Mbandaka (14.8 per cent) and S. Livingstone (14.1 per cent) were the four most common serovars in 2009, together making up 61.9 per cent of all incidents. S. Enteritidis, which was the most common serovar in 2008 (31.9 per cent of incidents) and in 2007 (18.9 per cent of incidents) was ranked fifth (5.9 per cent of incidents) in 2009.

Figure 6.1. Incidents of Salmonella serotypes in chickens in GB in 2009

S. Enteritidis and S. Typhimurium, which are regulated serovars for all production types (breeders, layers and broilers), accounted for 5.9 per cent and 4.8 per cent of incidents respectively. Of the total number of S. Enteritidis incidents recorded (n=26), 15 (58 per cent) originated from statutory sampling, and of the total number of S. Typhimurium incidents recorded (n=21), 12 (57 per cent) originated from statutory sampling. Although the numbers from 2009 should not be compared directly to previous years because of the extension of the NCP to broilers, a marked decrease of the overall number of S. Enteritidis incidents (26 in 2009 compared to 80 in 2008) can be seen. Even though 2008 saw a peak in S. Enteritidis incidents compared to the previous years, which was mainly due to the introduction of the layer NCP in 2008, there were fewer S. Enteritidis incidents reported in 2009 than in 2007, indicative of the successful reduction of the number of layer flocks positive for S. Enteritidis.

S. Hadar, S. Virchow and S. Infantis, which are regulated serovars for breeding flocks only, were detected at very low levels and not in breeding flocks. One S. Infantis incident was reported from a layer flock and two S. Virchow incidents were reported from broiler flocks, all originating from statutory testing. No S. Hadar incidents were reported in 2009.

All of the non-regulated top serovars in 2009 (S. Kedougou, S. Senftenberg, S. Mbandaka, S. Livingstone. S. Ohio and S. Montevideo) have been among the top ten serovars since 2005, although the numbers of incidents, especially for S. Kedougou, S. Senftenberg, S. Mbandaka, S. Livingstone and S. Montevideo, have increased considerably since 2008. This is due to an increase in incidents from broiler flocks.

A difference between production types can be observed in the ranking of the most common serovars. For broilers, S. Kedougou was the most common serovar (25.2 per cent), followed by S. Mbandaka (20.1 per cent), S. Livingstone (18.2 per cent), S. Senftenberg (11.3 per cent) and S. Ohio (6.2 per cent). In layers, S. Senftenberg was the most common serovar (24.4 per cent) as it was isolated from chick box liners on several occasions, followed by S. Enteritidis (13.7 per cent), S. Typhimurium (12.2 per cent), S. Mbandaka (6.9 per cent) and S. Agona (6.1 per cent). For the breeders, S. Senftenberg was the most common serovar (32.1 per cent), followed by S. Livingstone (14.3 per cent). Interestingly, all S. Senftenberg and S. Livingstone incidents from breeding flocks occurred outside statutory surveillance (i.e. were detected through voluntary surveillance, from hatchery samples, and not linked to a specific breeding flock) and are therefore not listed in the NCP section of this chapter. These serovars are known to be common hatchery-associated serovars, which may become resident in hatcheries despite absence of current infection in the source breeding flocks.

Five serovars were isolated in 2009, which had not been isolated at least since 2005. These were: one incident of S. Champaign from a broiler breeder flock; one incident of S. Ealing from a pet chicken, one incident of S. Fluntern from a broiler flock; one incident of S. Oranienburg from a layer breeder flock and three incidents of S. Ouakam from laying hen flocks from three different holdings. S. Gallinarum was not isolated from chickens in 2009, with the last incident dating back to 2007. Two incidents of S. Pullorum were recorded in 2009, originating from pet chickens from the same premises.

National Control Programme for Salmonella in Breeding Flocks of Chickens

Commission Regulation (EC) No. 1003/2005³ set a transitional target for the breeding flock sector to ensure that no more than 1 per cent of adult breeding flocks with more than 250 birds were positive for regulated Salmonella serovars (S. Enteritidis, S. Typhimurium, S. Virchow, S. Hadar and S. Infantis) by the end of 2009. In March 2007, the Poultry Breeding Flocks and Hatcheries Order came into force in Great Britain, which set out requirements for registration and sampling in a new National Control Programme (NCP)⁴ designed to monitor progress towards this target.

In January 2008, the PBFHO was revoked and replaced in England by the Control of Salmonella in Poultry Order (CSPO) 2007⁵, which also included requirements for the implementation of a NCP for laying flocks. Parallel legislation was subsequently introduced in Wales and Scotland⁶. The sampling protocol since April 2009 has reflected Commission Regulation (EC) No. 213/2009⁷, an amended version of Commission Regulation (EC) No. 1003/2005, introduced in April 2009. This contains the possibility of derogations to reduce operator and official control sampling frequency and adds the collection of one pair of boot swabs plus a dust sample as a permissible sampling option in adult (in-lay) flocks. As the UK breeding sector met the EU target for two consecutive years (2007 and 2008), breeding companies could, at the discretion of the Competent Authority, reduce the frequency of operator sampling from bi-weekly to every third week during the production phase. Similarly, the mid-lay official control sample was also no longer mandatory, reducing the number of official control samples to be collected from three to two. Some breeding companies have chosen to retain the previous more intensive sampling regime for producer samples in some or all of their breeding flocks.

While the EC target is focussed on regulated serovars in adult flocks only, Regulation (EC) No 2160/2003 (and in turn the NCP) requires sampling in both in-rear and adult flocks, and VLA has been monitoring test results from both stages.

Positive Flocks Identified in the NCP for Breeding Flocks in 2009

Data on positive findings of Salmonella in breeding flocks are reported in terms of positive flocks, as required by legislation (Regulation 213/2009). Multiple positive flocks on the same holding are counted separately.

When a breeding flock of Gallus gallus is suspected of being infected with Salmonella Enteritidis or Salmonella Typhimurium the flock is immediately placed under official control by the Competent Authority.

A summary of positive flocks and numbers of flocks testing positive for individual serovars is given in Table 6.3.

Under the statutory testing programme, 20 chicken breeding flocks in GB (19 adult flocks and one in-rear flock) were found positive for any Salmonella spp. Only two of the adult flocks (and no immature flocks) were positive for a regulated serovar (both Salmonella Typhimurium and both identified from official control samples) which results in a prevalence of 0.15 per cent of the 1,378 adult flocks tested under the NCP in Great Britain. This figure is well below the EC target of 1 per cent and compares with values of 0.07 per cent in 2007 (one adult flock positive for S. Typhimurium) and 0.54 per cent in 2008 (eight adult flocks positive for S. Typhimurium). There have been no reports of S. Enteritidis in breeding flocks during the three years of statutory testing under the NCP. Non-regulated serovars were isolated from 17 adult breeding flocks and one immature breeding flock tested under the NCP during 2009. The most prevalent serovar isolated from breeding flocks was S. Dublin, which was isolated from ten flocks on four broiler breeder holdings. Interestingly, S. Dublin was not recorded from any other production type in 2009, but was also isolated from two breeding flocks under the NCP in 2008. An investigation into these unusual findings was unable to identify the source.

S. Thompson, which was isolated from two flocks on the same holding, was also isolated from five breeding flocks in 2008. S. Agama, S. Oranienburg, S. Saintpaul and Salmonella 3,19:-:- were each isolated from breeding flocks in 2009 only, but not in 2008. The same applies to S. Champaign, which was isolated from an immature flock in 2009 only. S. Agama was not isolated from breeding flocks in 2008, but accounted for eleven broiler breeder incidents in 2007. While S. Mbandaka was the second most common serovar in broilers in 2009, it is only found occasionally in other production types, including breeding flocks.

National Control Programme for Salmonella in Chicken Egg Laying Flocks

Commercial laying flocks are subject to statutory Salmonella testing programmes in order to fulfil the requirements of EU legislation (Directive 2003/99/EC of the European Parliament and of the Council, Regulation (EC) No. 2160/2003 of the European Parliament and of the Council, Commission Regulation (EC) No. 1168/2006 and Commission Regulation (EC) No. 1237/2007)⁸.

In the EU baseline survey on the prevalence of Salmonella in laying flocks conducted in 2004/2005⁹, about eight per cent of layer flock holdings in the UK were found to be positive for S. Enteritidis and/or S. Typhimurium. A target was set (Regulation (EC) No. 1168/2006) to annually reduce the number of adult laying flocks positive for these serovars by at least 10 per cent compared with the previous year, starting in 2008, to a maximum of two per cent of flocks remaining positive for the regulated Salmonella serovars.

All Member States were required to have a National Control Programme (NCP) in place by February 2008. The National Control Programme for Salmonella in layers¹⁰ includes all commercial egg laying flocks except where producers supply small quantities direct to the final consumer (Regulation (EC) No 2160/2003, Article 1 paragraph.3).

The NCP in England is enforced by The Control of Salmonella in Poultry Order 2007¹¹, and there is separate, equivalent legislation for Scotland and Wales¹². According to Commission Regulation (EC) No. 1237/2007, eggs from flocks with an unknown Salmonella status or those that tested positive for either S. Enteritidis or S. Typhimurium must not be used for direct human consumption (as table eggs) as of the 1st of January 2009¹³.

According to Commission Regulation (EC) 1237/2007¹⁴, in case of a flock being positive for either S. Enteritidis or S. Typhimurium, the operator can request additional confirmatory testing of 4,000 eggs, the internal organs of 300 birds, or five faecal and two dust samples per flock. The collection of these samples is carried out by the Competent Authority, and restrictions remain in place until the results are known.

Positive Flocks Identified in the NCP for Laying Flocks

For the purposes of reporting results of the NCPs to the European Commission, every positive flock is counted, irrespective of the number of positive flocks on a given farm at any one time.

A summary of positive flocks detected within the NCP in 2009 and the numbers of flocks positive for each serovar by status of sampling are shown in Tables 6.5 (adult flocks) and 6.6 (in-rear flocks).

Under the statutory testing programme, 105 laying flocks (67 adult flocks and 38 in-rear flocks) were detected as positive with any Salmonella serovar in 2009.

Of the 67 positive adult flocks, seven were positive for S. Enteritidis, and three were positive for S. Typhimurium; none were positive for both. Compared with 2008, there was a marked reduction in reports of S. Enteritidis; in 2008 there were 49 (73.1 per cent) positive flocks whereas in 2009 there were only seven (10.4 per cent). The total number of incidents involving any serovar was similar in both years, demonstrating a relative reduction in the regulated serovars. The number of adult flocks positive for S. Typhimurium remained nearly the same (4 flocks in 2008 versus 3 flocks in 2009).

Of the 38 in-rear (immature) positive flocks, seven were infected with S. Typhimurium, and the remaining 31 were infected with non-regulated serovars, of which 28 were positive for S. Senftenberg. This compares with 14 Salmonella - positive immature flocks in 2008, of which four tested positive for S. Enteritidis, one tested positive for S. Typhimurium and ten tested positive for non-regulated serovars, including six flocks positive for S. Senftenberg.

The high relative frequency of S. Senftenberg in chickens overall (Table 6.1) was mirrored in layer flocks, in which it was the most common serovar; however, it was predominantly found in immature flocks and only to a much lesser extent in adult flocks. S. Kedougou was the most common serovar amongst chickens overall (Table 6.1), but only accounted for two positive layer flocks (3.0 per cent). S. Agona and S. Anatum were relatively common serovars in laying flocks yet there were no cases of either in broiler flocks (Table 6.8).

Using the number of laying flocks subject to at least one official test during 2009 as the denominator population, the estimated prevalence of Salmonella positive adult egg laying flocks in Great Britain from statutory testing was 1.60 per cent (67/4,197) in 2009. The estimated prevalence of Salmonella Enteritidis and/or S. Typhimurium in adult egg laying flocks in Great Britain was 0.24 per cent (10/4,197) in 2009, well below the definitive target of 2 per cent. This compares with an estimated prevalence of 1.25 per cent for all serovars and 1 per cent for S. Enteritidis and/or S. Typhimurium in 2008. The considerable reduction in Salmonella prevalence since the EU baseline survey of 2004/05, while not directly comparable to the NCP monitoring results due to different sampling methods and denominator data, does indicate that substantial progress continues to be made in controlling Salmonella in the layer sector.

National Control Programme for Salmonella in Broiler Flocks

In the EU baseline survey on the prevalence of Salmonella in broiler flocks, conducted in 2005/2006¹⁵, S. Enteritidis was not isolated from any commercial broiler holdings and S. Typhimurium was reported from only one eligible holding, giving an estimated prevalence of 0.3 per cent for these serovars for the UK. A target was set (Regulation (EC) No 646/2007) for a maximum of 1 per cent of broiler flocks to remain positive for S. Enteritidis and S. Typhimurium by December 2011.

A National Control Programme (NCP) for Salmonella in broiler flocks was implemented in 2009¹⁶. All flocks of chickens reared for meat are included unless exempted in Regulation (EC) No. 2160/2003 under Article 1.3, i.e. birds produced for private domestic consumption, or where there is direct supply of small quantities of products to the final consumer or to local retail establishments directly supplying the primary products to the final consumer.

The NCP in England is enforced by The Control of Salmonella in Broiler Flocks Order 2009 (CSBO) and there is separate equivalent national legislation for Scotland and Wales.

Positive Flocks Identified in the NCP for Broiler Flocks in 2009

For the purposes of reporting results of the NCPs to the European Commission, every positive flock is counted, irrespective of the number of positive flocks on a given farm at any one time.

A summary of positive flocks detected in the statutory control programme in 2009 and numbers of flocks positive for each serovar by status of sampling is shown in Table 6.8.

Statutory testing resulted in a total of 363 broiler flocks positive for any Salmonella serovar in 2009. Of those, ten broiler flocks were positive for S. Enteritidis (all originating from a single contamination incident involving S. Enteritidis PT8 in imported hatching eggs from outside the EU), two for S. Typhimurium, and two for S. Virchow. The four most common serovars in broiler flocks (S. Kedougou, S. Mbandaka, S. Livingstone and S. Senftenberg) were also the four most common serovars in chicken incidents overall (Table 6.1).

As this is the first year of the broiler NCP, no comparisons can be made with previous years.

There were approximately 27,000 broiler flocks tested according to the requirements of the Salmonella NCP during 2009, which gives an estimated prevalence of 0.04 per cent for the target Salmonella serovars for the GB for 2009. This is well below the target 1 per cent specified in the legislation, and the UK as a whole has one of the lowest Salmonella prevalence levels in the EU.<.p>

References

¹ http://www.defra.gov.uk/evidence/statistics/foodfarm/landuselivestock/junesurvey/documents/RegCountUA_09.xls
http://www.scotland.gov.uk/Resource/Doc/326399/0105175.pdf
http://wales.gov.uk/docs/statistics/2009/091110sdr1822009en.pdf

² Salmonella in Livestock Production in GB (2008 report)
Salmonella in Livestock Production in GB (2007 report)

³ http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2005:170:0012:0017:EN:PDF

⁴ http://www.defra.gov.uk/foodfarm/farmanimal/diseases/atoz/zoonoses/documents/Salmonella-breeders.pdf

⁵ http://www.legislation.gov.uk/uksi/2007/3574/contents/made

⁶ http://www.legislation.gov.uk/wsi/2008/524/contents/made
http://www.legislation.gov.uk/ssi/2008/266/contents/made

⁷ http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:073:0005:0011:EN:PDF

⁸ http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2003:325:0031:0040:EN:PDF
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2003:325:0001:0015:EN:PDF
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2006:211:0004:0008:EN:PDF
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2007:280:0005:0009:EN:PDF

⁹ http://www.efsa.europa.eu/EFSA/Report/zoon_report_ej97_finlayinghens_en,1.pdf

¹⁰ http://www.defra.gov.uk/foodfarm/farmanimal/diseases/atoz/zoonoses/documents/Salmonellalayers.pdf

¹¹ http://www.defra.gov.uk/foodfarm/farmanimal/diseases/atoz/zoonoses/documents/statutoryinstrument.pdf

¹² http://www.legislation.gov.uk/wsi/2008/524/contents/made
http://www.legislation.gov.uk/ssi/2008/266/contents/made

¹³ http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2007:280:0005:0009:EN:PDF

¹⁴ http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2007:280:0005:0009:EN:PDF

¹⁵ http://www.efsa.europa.eu/EFSA/efsa_locale-1178620753812_1178620761745.htm

¹⁶ http://www.defra.gov.uk/foodfarm/farmanimal/diseases/atoz/zoonoses/documents/Salmonellabroilers.pdf

Further Reading

-

You can view the full chapter Reports of Salmonella in Chickens (including detailed tables) by clicking here.

Further Reading

-

You can view the full report Salmonella in Livestock Production in GB 2009 by clicking here.