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UK Survey of Campylobacter and Salmonella in Fresh Chicken

by 5m Editor
6 October 2009, at 12:00am

A UK-wide survey was undertaken by the Agency between May 2007 and September 2008 to determine Campylobacter and Salmonella prevalence on fresh chicken at retail.

During the course of the survey, 3,363 samples were collected, with 3,274 being acceptable for testing and microbiological examination using a presence/absence method for the detection of Campylobacter and Salmonella. Campylobacter enumeration tests were conducted on 927 samples, collected between April 2008 and August 2008.

Campylobacter

It is well recognised that Campylobacter can be a difficult organism to isolate in the laboratory and that the presence/absence method has limitations.

This may, in turn, lead to underestimates of prevalence. In this survey the Campylobacter prevalence detected using the enumeration method was higher (50.5 per cent) than that by the presence/absence method (33.9 per cent) for the 927 samples tested.

The overall prevalence and prevalence for UK-origin chicken is reported based on the combined data for those samples tested using both presence/absence and enumeration methods (n=927).

This approach has been taken in some recent studies to provide a more accurate measure of Campylobacter prevalence in food samples. The prevalence of Campylobacter in chicken at retail in the UK was 65.2 per cent, based on the results from both methods combined, for the 927 samples tested.

The prevalence of Campylobacter in whole chicken of UK-origin was 76.1 per cent, based on the results from both methods combined, for the 416 whole UK-origin chicken samples tested.

The change in approach taken to determine prevalence in this survey means that it is no longer valid to make direct comparisons to the 2005 baseline of 70 per cent.

However, this data provides the Agency with a more robust evidence base for setting targets. Underlying trends for Campylobacter are reported for the 3274 samples tested using the presence/absence method only.

Overall, the species Campylobacter jejuni accounted for 52.9 per cent of the Campylobacter isolates found in the survey, whereas C. coli made up 47.1 per cent.

Although C. jejuni continues to be seen more frequently on chicken at retail this finding indicates an increase in the proportion of isolates identified as C. coli since the 2001 survey was conducted. The public health significance of this finding is unclear.

A total of 1519 Campylobacter isolates were tested for their sensitivity to a series of antimicrobial drugs. Of these isolates, 197 (13.0 per cent) were sensitive to all the drugs tested. This figure represents an increase in the frequency of antimicrobial resistance among Campylobacter isolated from retail chicken compared to that seen in the 2001 survey.

There has also been an increase in resistance to the quinolones, ciprofloxacin and nalidixic acid. The increase in resistance may, in part, be due to a decrease in the concentration of ampicillin used (from 32mg/l to 8mg/l) to test resistance. The prevalence of Campylobacter was higher for chilled chicken (47.6 per cent) than for frozen (13.6 per cent).

The enumeration results, from the 927 samples tested also show that, when detected, levels of Campylobacter (colony-forming units per sample; cfu/sample) were significantly lower (p=0.006) on frozen samples. The prevalence of Campylobacter was similar for both whole and portioned samples and skin-on and skin-off portions.

However, median levels of Campylobacter detected on samples was higher on whole carcasses (160 cfu/sample) and skin-on portions (60 cfu/sample) when compared to portions (26 cfu/sample) and skin-off (18 cfu/sample) respectively. Campylobacter prevalence was higher in samples from chicken reared using free-range (51.3 per cent) or organic (60.4 per cent) production systems than that recorded for housed birds (42.6 per cent). The median levels of Campylobacter enumerated on housed samples (91 cfu/sample) exceeded that for free-range (80 cfu/sample) or organic (66 cfu/sample).

However the sample size for chicken reared using free-range or organic systems was too small to make statistical comparisons between prevalence.

The data indicates some variation in the prevalence of Campylobacter according to the retailer type – major supermarkets (44.4 per cent), other supermarkets (41.9 per cent), butchers (32.3 per cent), farm shop (33.0 per cent) and market stall (0.0 per cent). However, when tested statistically, this variation was not found to be significant.

Campylobacter prevalence in poultry flocks is known to vary with season, showing a pronounced summer peak.

This survey was not designed to investigate seasonality but Campylobacter prevalence did vary over the course of this survey according to the month of purchase. The highest prevalence was detected in August 2007 (68.1 per cent) and the lowest in May 2008 (28.8 per cent).

However the results do not show a similar trend to that normally observed in poultry flocks.

Salmonella

Salmonella was found in 207 samples giving a weighted prevalence of 6.6 per cent. This indicates that Salmonella prevalence has remained low since the 2001 survey, which reported a prevalence of 5.7 per cent.

Thirty different Salmonella serotypes were isolated during the survey.

S. Kentucky and S. Bredeney were found most frequently, accounting for 11.5 per cent and 9.7 per cent of the isolates respectively.

S. enteritidis (7.0 per cent) was the seventh most common serotype and S. typhimurium (1.8 per cent) the fourteenth. Of the 16 S. enteritidis isolates, seven (43.8 per cent) were phage typed as PT4 and 6 (37.5 per cent) as PT5c.

Three (75 per cent) of the S. typhimurium isolated were typed as DT120, with 1 (25 per cent) found to be DT104. All salmonellas are potentially pathogenic therefore the change in the pattern of serotypes observed is of limited public health significance. Of the 227 Salmonella isolates tested for their sensitivity to a number of antimicrobial drugs, 134 (59.0 per cent) were sensitive to all of the drugs tested.

This indicates a decrease in antimicrobial resistance from the 2001 survey (46 per cent isolates fully sensitive); this may reflect differences in the serotypes isolated. All 14 isolates of S. Java PT Colindale were found to be multi-drug resistant.

Three of these were resistant to one or more cephalosporins and seven were resistant to both cephalosporins and the fluoroquinolone ciprofloxacin. This is the first report of S. Java with this resistance pattern isolated from food in the UK. These isolates will be fully characterised as part of another project to determine the mechanism of resistance.

Salmonella prevalence was significantly higher (p<0.001) in chicken of non-UK origin (11.3 per cent) compared to that of UK-origin (5.7 per cent). The frequency of contamination was higher for frozen chicken (11.7 per cent) than for chilled chicken (5.9 per cent).

The overall Salmonella contamination rate was higher in whole chicken compared to chicken portions at retail (6.9 per cent vs 6.3 per cent). The frequency of Salmonella contamination present on chicken portions with skin-on was 6.6 per cent, while those without skin had a prevalence of 6.1 per cent.

Conclusions

A significant proportion of fresh chicken on sale in the UK remains contaminated with Campylobacter.

As such, Campylobacter in poultry continues to be a priority for the Agency in terms of foodborne disease risk, highlighting a continuing need to work with industry to address this.

There have been shifts in the Campylobacter spp. and Salmonella serotypes isolated since the 2001 survey. Antimicrobial resistance levels have also changed.

Human Salmonella and Campylobacter infections, however, are rarely treated with antibiotics and the primary concern is the presence of these organisms on food.

Further Reading

- You can view the full report by clicking here.

October 2009