10th Year Anniversary of Veterinary Public Health Centre for Asia Pacific 2-6 July 2013 The Imperial Mae Ping Hotel, Chiang Mai, THAILAND
Quantifying Salmonella Contamination in Pig Slaughterhouses in Hung Yen, Vietnam Sinh Dang Xuan1,2,* Hung Nguyen-Viet2 Tongkorn Meeyam3,4 Reinhard Fries5 Joint Master Course in Veterinary Public Health (MVPH) of Freie Universität Berlin, Germany and Chiang Mai University, Thailand 2 Center for Public Health and Ecosystem Research (CENPHER), Hanoi School of Public Health, 138 Giang Vo, Hanoi, Vietnam 3 Department of Veterinary Biosciences and Veterinary Public Health, Faculty of Veterinary Medicine, Chiang Mai University, Thailand 4 Veterinary Public Health Centre for Asia Pacific (VPHCAP), Faculty of Veterinary Medicine, Chiang Mai University, Thailand 5 Institute of Meat Hygiene and Technology, Freie Universität Berlin, Brümmer Str. 10, Berlin D-14195, Germany *Corresponding author; Email:
[email protected],
[email protected] 1
ABSTRACT The risk of Salmonella contamination along the pork production is a worldwide concern. Not only the biological contamination, but also personal perception and individual behavior play a role for risk assessment along a chain. This study is to identify the prevalence and number of Salmonella in 3 pig slaughterhouses in relation to several risk factors. During January to April 2013, a total of 87 samples (carcasses, workers’ hands, cutting board and belly skin material) were collected from 4 visits to each slaughterhouse. A 3-tube Most Probable Number (MPN) was applied to quantify the number of Salmonella from carcass, workers’ hands, cutting board and belly skin samples (35 samples). The result showed that Salmonella prevalence was 36.9% (26.7-47.8%), mostly found on worker’s hands (50%) and the lowest from cutting board (33.3%). The highest number of Salmonella on carcass and cutting boards was less than 0.075 MPN/cm2 and 1.2 MPN/cm2, respectively. Potential risk factors were tested however they were not statistical significant. This study underlines the necessity of good hygiene practices and management in slaughterhouses. In terms of food safety, further risk assessment of Salmonella in pork production chains is needed. KEYWORDS: Hygienic practice, pig slaughterhouse, risk factors, Salmonella, Vietnam
INTRODUCTION Salmonella is one of the main causes of foodborne illnesses in humans. Pork, after poultry meat, is a major source of human foodborne salmonellosis in the European Union (1). In Vietnam, from 2007 to 2011, 927 outbreaks of food poisoning occurred, with 30,734 cases and 230 deaths (2). Pork and pork products are most popular in Vietnam and distributed mostly by the traditional ways,
i.e., small-scale slaughter, retail and pork producers where the risk of microbial contamination pork is relatively high. Along the slaughter line, several steps can be critical with regard to Salmonella contamination: dehairing, removal of the intestines (3), washing, splitting the carcass. During these steps, the carcass can be contaminated with feces and bacteria can spread onto the carcass and to following
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10th Year Anniversary of Veterinary Public Health Centre for Asia Pacific 2-6 July 2013 The Imperial Mae Ping Hotel, Chiang Mai, THAILAND
carcasses. Some studies on Salmonella prevalence in slaughterhouses in Vietnam showed that Salmonella contamination in water, on the floor, weighting bowls, cooking boards were between 16% and62%, on carcasses at slaughterhouse level ranging from 15% to 95%. At market, the Salmonella prevalence in pork was between 33 and 69% (4-5). To understand the risk and magnitude of Salmonella contamination in a slaughterhouse, the objectives of this study were to identify the prevalence and number of Salmonella in pig slaughterhouses in Vietnam and to identify related risk factors. MATERIALS AND METHODS Sample collection Pig slaughterhouses: Three pig slaughterhouses were selected in Hung Yen province including Van Giang, Van Lam and My Hao district. Each slaughterhouse was visited 4 times during January to April 2013. The capacity of these slaughterhouses was about 10-40 pigs per day with 4-6 permanent workers. Each visit was carried out in the early morning from 2 am till 5 am, sampling started after slaughter of 2-3 pigs and randomly for next samples. Sample collection: In total, 87 samples were collected including 47 carcass swabs, 12 workers hands, 12 cutting boards and 16 samples by cutting tissue from the belly skin. Carcass swabs and belly skin samples:400 cm2 of split carcasses were swabbed at 4 different sites (hind limb-medial, abdomenmedial, mid-back and lower part of neck) (ISO 17604:2003). While skin samples were taken from belly, and put into sterilized plastic bag before transportation to laboratory. Environmental samples: Worker’s hand, cutting board swab samples were collected by using sterilized gauze during the processing. Two hands were swabbed on 2 sides and between the fingers. The cutting board was swabbed in an area of 25cm2. Microbiological analysis All samples were stored in a cool box and transported to the laboratory. 25 g of belly skin samples were taken and homogenized
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with 225 ml Buffered Peptone Water (BPW). Carcasses swab and environmental samples were added up to 100 ml BPW for homogenization. All homogenates were incubated at 37 °C for 16-20 h. Salmonella isolation: Salmonella was isolated from carcass and environmental samples based on ISO 6579:2002/Amd 1:2007 (6). Salmonella Most Probable Number: Salmonella quantification was done by using the 3-tube MPN method (7). After 16-20h the Salmonella incubation at 37oC, identification was performed according the previous mentioned procedure. The number of Salmonella positive tubes in each dilution was used to calculate the number of Salmonella(8). Data collection A checklist and a questionnaire were developed, tested and applied to obtain information at slaughterhouse level. The checklist was used to observe biosecurity, hygienic measures and technical practice in slaughterhouse. Questionnaires were applied to get about information of slaughtered pigs in each visit day.
Data analyses Checklist and questionnaire were used for statistical analyses to test for related risk factors for Salmonella contamination. Odds ratio (OR), Chi square and Fisher’ exact tests were used to determine significant factors leading to Salmonella positive result. R Studio (0.96.316) and MS Excel-2007 were used for data analyses. RESULTS General information of slaughterhouses Result from questionnaires and recording sheets concentrate on variables linked to pig origin, transportation and lairage time. These results showed information from preslaughter stage of the 3 slaughterhouses (Table 1). Information was obtained in relation to biosecurity, hygienic measures and technical practice.
10th Year Anniversary of Veterinary Public Health Centre for Asia Pacific 2-6 July 2013 The Imperial Mae Ping Hotel, Chiang Mai, THAILAND
Hygienic practice: Slaughter and processing in these slaughterhouses was done on the floor with limited separation areas for bleeding, scalding, or dehairing. All 3 slaughterhouses had an experienced worker assigned for evisceration. In 2 slaughterhouses, water stored in a tank was used to wash the floor, carcasses, hands and equipment. The other slaughterhouse used pipeline water directly to wash the floor, carcasses, and hands. All of the 3 slaughterhouses used biogas to treat the waste. Table 1: Mean of variables recorded from pig transportation and lairage time. Variables No.of pig transport/time Transport duration Transport distance Time arrived at lairage Time spent in lairage
Unit
n
head 12
Mean
SD
Min
max
23
7
17
40
hour
12
1.76
1.24
0.5
4.17
km
12
60.8
50.4
15
150
clock 12
13.9
4.17
10
22
hour
13.1
4.17
5
17
12
For biosecurity, the 3 slaughterhouses carried out a separation of individual herds. Through 12 observations, abnormal signs, thin, or sick pigs were not seen in lairage. Hygiene measures: One slaughterhouse had a separate entrance for pigs. People could access freely into the slaughter area. Workers frequently used boots, however they wore uniforms or apron rarely. Salmonella prevalence Overall, Salmonella was isolated from 36.9% (32/87) of all samples collected and from 34.9% (22/63) of carcass samples. Salmonella was mostly obtained from workers’ hands, with 50% (6/12) and less frequently from belly skin samples, with 18.8% (3/16) (Table 2). Quantification of Salmonella The highest number of Salmonella on carcass and cutting boards was less than 0.075 MPN/cm2 and 1.2 MPN/cm2, respectively, and less than 0.3 MPN/g from belly skin. Salmonella enumeration from workers’ hands ranged from 0 to 7.0 MPN/hand (Table 3).
Table 2: Salmonella prevalence from different sample types in 3 slaughterhouses. Prevalence_% (No. positve result/n)
Sample type SH A
SH B
SH C
Overall
Carcass surface
23.5 (4/17)
46.7 (7/15)
53.3 (8/15)
40.2 (19/47)
Belly skin
25.0 (1/4)
16.7 (1/6)
16.7 (1/6)
18.8 (3/16)
Workers’ hand
25.0 (1/4)
100 (4/4)
25.0 (1/4)
50.0 (6/12)
Cutting board
25.0 (1/4)
50.0 (2/4)
25.0 (1/4)
33.3 (4/12)
Overall
24.1 (7/29)
48.3 (14/29)
37.9 (11/29)
36.9 (32/87)
SH A, B, C: Slaughterhouse A, B and C
Table 3: Salmonella number from different sample types in 3 slaughterhouses. Sample types
Unit
No. of Salmonella
95% CI
Carcass surface
MPN/cm2
