April 28, 2019 Critical Thinking

Research Paper: Quantitative risk assessment of human salmonellosis in the smallholder pig value chains in urban of Vietnam (Dang-Xuan et al., 2017)
General Context
Meat and meat products are consumed on a large scale worldwide. In Vietnam, the total consumption of pork is 70% and pig production is the main source of income for more than 4 million small farmers in the country (Nga et al., 2015). The per capita pork consumption of Vietnam population is approximately 29 kg (OECD, 2018). Consumption of pork can result in a disease known as Salmonellosis. Salmonellosis is one of the most common type of foodborne illness throughout the world. It is considered as a biggest problem by the Ministry of Health, Vietnam. It is caused by Salmonella which is a gram negative bacteria belonging to the family of Enterobacteriaceae and consists of two species namely S. Enterica and S. Bongori (Yokozawa, 2014). Salmonella strains are present in wide range in the intestinal tract of warm and cold-blooded animals. Salmonella can infect a wide range of hosts including man, insects, birds, etc. Salmonella infections occur mainly due to the consumption of food containing animal faeces. Water is also identified as a source of Salmonella in food. Two serovars namely S. Typhi and S. Paratyphi can cause fever and are known as typhoid strains. Non typhoidal strains are S. Typhimurium and S. Enteriditis (Baer, Miller, & Dilger, 2013). Non typhoidal Salmonella infections cause gastroenteritis. Contaminated foods of animal origin could not be recognized because there is no change in their smell or appearance. Salmonella can be killed by proper cooking however, unhygienic conditions of the workers working in slaughterhouse may result in contamination (Thai, 2007). Salmonella contamination can occur at any point in the food chain for example at farm, during processing or distribution. Main source of salmonella contamination is the slaughterhouse. Once the salmonella present on carcass gets favourable conditions, it multiplies to harmful levels (Malorny, Löfström, Wagner, Krämer, & Hoorfar, 2008). Various studies have been conducted to find the prevalence of Salmonella in pork and all have reported the presence of Salmonella in high amounts (Van, Moutafis, Istivan, Tran, & Coloe, 2007). However, the extent of risk depends on several factors such as consumption pattern and cooking methods. In Mekong Delta Harbor of Vietnam, Salmonella is found in high amounts in pigs, chicken and ducks. Contamination of Salmonella in pork was found to be higher than that in some developed countries (PHAN et al., 2005).
Aspect of Food Safety Risk Assessment covered by the article
The article which is discussed here covers the quantification of risk of salmonellosis in humans through the consumption of pork in urban areas of Vietnam. Salmonella was identified as the hazard and dose response and bacterial growth models were obtained from literature. Salmonellosis is more prevalent in Vietnam because of high consumption of pork. It is more fatal to children as compared to adults. Three out of ten districts in the Hung Yen province of Vietnam. Household producers of pigs were classified as small, medium and large based on the number of pigs they had. Slaughterhouses were classified as small and medium based on the number of pigs slaughtered per day. At retail level, classification was based on roadside vendors, commune markets and central markets. Total of 36 pig farms were selected for sampling. Swabs of four different sites of pen floor and final carcass were collected. In slaughterhouse, pigs were selected randomly based on the total number of pigs slaughtered in that slaughterhouse. From retail market, 108 cut pork samples were collected. The National Institute of Veterinary Research, Hanoi, Vietnam tested the samples for the presence or absence of Salmonella. The prevalence of Salmonella increased from slaughterhouse to the retail pork cuts thus suggesting that Salmonella contamination is occurring throughout the entire supply chain. Exposure assessment was performed using data from consumer surveys. Structured questionnaire was used for survey along with a focus group discussion where the cooking methods and consumption pattern was discussed based on gender and age group. From the focus group discussion, it was found that a person consumed on an average 74 g boiled pork/meal and this amount varied by age (37 g/meal – children, 100 g/meal – adult) and gender (87 g/meal – adult female, 73 g/meal – adult male). Furthermore, cross-contamination was also considered as a source of salmonella in pork. Four different scenarios were analysed for cross-contamination. The use of same knife and cutting board for raw and cooked pork had the highest cross-contamination rate. For risk characterization step of risk assessment, dose-response and exposure assessment were combined and a risk model was developed. The effect of temperature on the growth of Salmonella species was predicted using predictive microbiology models. The annual incidence rate was estimated to be the lowest in children as compared to adults. Pork can become contaminated from Salmonella at the breeding or fattening farm, during transportation, lairage or slaughter. Infection with Salmonella during transport or lairage could be due to stress, contact with excreting pigs, improperly cleaned truck (Swanenburg, van der Wolf, Urlings, Snijders, & van Knapen, 2001).
Novelty of the article
Salmonella infections in humans are major economic problem (Tirado & Schmidt, 2001). Majority of Salmonella serovars can cause non-typhoidal infections in humans. Due to globalization and an increase in travel among people, these types of infections are becoming an issue throughout the world. A contaminated product produced in one country may be consumed in another country and it may result in an outbreak. Salmonella infections are transmitted mainly through contact with animals, contaminated water or consumption of contaminated animal products such as raw meat, pork, chicken and so on (Vo et al., 2006). It is crucial to understand this agent, its behaviour, propagation and the incidence rate in Vietnam because of large scale consumption of pork and chicken which is discussed above. Risk analysis is not properly understood and applied in some developing countries like Vietnam due to lack of resources and manpower. Establishing a risk assessment model is required in Vietnam’s informal market because most of the domestically produced food is sold there. Selected research article provides an entire risk assessment on human salmonellosis in pig value chain which could provide valuable information to scientists and policy makers regarding the risk present and helps in identification of points in the supply chain where control measures need to be implemented. The article discussed here is the first published QMRA model for food safety in Vietnam. QMRA models help in identifying the risks and factors that affect food safety. These models require quantitative microbiological data which is still hampered and therefore assumptions are included which result in high degree of uncertainty (Malorny et al., 2008). This study focused on the importance of small and medium farmers and slaughterhouses in Vietnam. It further reveals the application of QMRA in the value chains and gives information regarding handling risks. QMRA models are applied mainly in developed countries and are in the initial stages in the developing countries. In the QMRA model developed in this article, the 90% confidence intervals are wide. The variability parameters (amount of pork consumed and salmonella concentration on the contaminated boiled pork) used had a wide variety.
The number and type of samples collected and analysed are discussed above the “Aspect of Food Safety Risk Assessment the article is covering”. Swab analysis of pen floor and carcass showed that the salmonella was present in higher amount on the carcass (41.7%) as compared to pen floor (33.3%). Among 40% of the carcass swabs were Salmonella positive. This is comparable to the finding of high income countries where 55% of the pork carcass was found to be Salmonella positive. Also, this study showed an increase in Salmonella prevalence along the food chain with around 40% of retail samples being positive. This value was very high in comparison to high income countries however, it was very low as compared to low income countries. Also, in this study cross-contamination due to the use of same knife and cutting board for raw and boiled pork was considered as the main contributor to human salmonellosis. Furthermore, interview of consumers revealed that more than half of them buy pork from central market and the rest buy from commune market. Finally, it was concluded that there were high levels of Salmonella along the smallholder pig value chain from farm to fork (retail pork) and some strict control measures needs to be taken to protect the health of the consumers. Some of these control measures include implementation of Good Agricultural Practices (GAP) at the farm level, proper infrastructure development for slaughter and public education regarding cross-contamination.
Although this study showed some significant findings, it had some limitations too. Some of the limitations are discussed below.
1. The reduction of Salmonella while cooking in household was uncertain. For studying various scenarios of cross-contamination, sampling from household was not done due to cost and ethical considerations.
2. The model developed in this study was not validated. Use of field data for attribution studies would have resulted in a more robust model. However, it was more expensive and challenging. There is a huge difference between the government reports and hospital cases which may be due to underreporting or underestimating.
3. The quantity and frequency of pork consumption depended on the individual and time. Therefore, the actual cross-contamination and concentration of Salmonella might be over-estimated.
4. The model developed in this study was not specific to any Salmonella strains. Also, it was not able to differentiate the susceptibility in different consumer groups.

Baer, A. A., Miller, M. J., ; Dilger, A. C. (2013). Pathogens of Interest to the Pork Industry: A Review of Research on Interventions to Assure Food Safety. 12(2), 183-217. doi:doi:10.1111/1541-4337.12001
Dang-Xuan, S., Nguyen-Viet, H., Unger, F., Pham-Duc, P., Grace, D., Tran-Thi, N., . . . Makita, K. J. I. J. o. P. H. (2017). Quantitative risk assessment of human salmonellosis in the smallholder pig value chains in urban of Vietnam. 62(1), 93-102. doi:10.1007/s00038-016-0921-x
Malorny, B., Löfström, C., Wagner, M., Krämer, N., ; Hoorfar, J. (2008). Enumeration of salmonella bacteria in food and feed samples by real-time PCR for quantitative microbial risk assessment. Applied and environmental microbiology, 74(5), 1299-1304. doi:10.1128/AEM.02489-07
Nga, N., Lapar, M. L., Unger, F., Van Hung, P., Duong, N. H., Huyen, N., . . . Thi Be, D. (2015). Household pork consumption behavior in Vietnam: Implications for pro-smallholder pig value chain upgrading.
OECD. (2018). Meat Consumtion (indicator). Retrieved from
PHAN, T. T., KHAI, L. T. L., OGASAWARA, N., TAM, N. T., OKATANI, A. T., AKIBA, M., ; HAYASHIDANI, H. (2005). Contamination of Salmonella in Retail Meats and Shrimps in the Mekong Delta, Vietnam. 68(5), 1077-1080. doi:10.4315/0362-028x-68.5.1077
Swanenburg, M., van der Wolf, P. J., Urlings, H. A. P., Snijders, J. M. A., ; van Knapen, F. (2001). Salmonella in slaughter pigs: the effect of logistic slaughter procedures of pigs on the prevalence of Salmonella in pork. International Journal of Food Microbiology, 70(3), 231-242. doi:
Thai, N. P. J. J. C.-F., MVPH thesis. (2007). Prevalence of Salmonella on Pig Carcasses at a Slaughterhouse in Hanoi, Vietnam.
Tirado, C., ; Schmidt, K. (2001). WHO surveillance programme for control of foodborne infections and intoxications: Preliminary results and trends across greater Europe. Journal of Infection, 43(1), 80-84. doi:10.1053/jinf.2001.0861
Van, T. T. H., Moutafis, G., Istivan, T., Tran, L. T., ; Coloe, P. J. (2007). Detection of Salmonella spp. in retail raw food samples from Vietnam and characterization of their antibiotic resistance. Applied and environmental microbiology, 73(21), 6885-6890. doi:10.1128/AEM.00972-07
Vo, A. T. T., van Duijkeren, E., Fluit, A. C., Heck, M. E. O. C., Verbruggen, A., Maas, H. M. E., ; Gaastra, W. (2006). Distribution of Salmonella enterica Serovars from humans, livestock and meat in Vietnam and the Dominance of Salmonella Typhimurium Phage Type 90. Veterinary Microbiology, 113(1), 153-158. doi:
Yokozawa, T. (2014). A study of Salmonella prevalence in pork value chain from pig slaughterhouses to markets in Hung Yen, Vietnam. BSc thesis in Veterinary Science, Hokkaido, Japan: Rakuno Gakuen University.,