Salmonella in pork can be combated during pre- or post-harvest. For large slaughterhouses, post-harvest measures like decontamination might be cost-effective while this is less likely with small-to-medium sized slaughterhouses. In this study, pre-harvest measures might be more relevant. We describe an extended surveillance-and-control programme for Salmonella in finisher pigs, which, to establish equivalence to the Swedish control programme, is intended for implementation on the Danish island, Bornholm. The effect of the programme on food safety was estimated by analysing Salmonella data from pig carcasses originating from herds that would have qualified for the programme during 2006-2008. Food safety was interpreted as prevalence of Salmonella on carcasses as well as the estimated number of human cases of salmonellosis related to pork produced within the programme. Data from the Danish Salmonella programme were obtained from Bornholm. We used a simulation model developed to estimate the number of human cases based on the prevalence of Salmonella on carcass swabs. Herds are only accepted in the programme if they have one or less seropositive sample within the previous 6 months. In this way, the Salmonella load is kept to a minimum. The programme is not yet in operation and pigs that qualify for the programme are currently mixed at slaughter with those that do not qualify. Therefore, we had to assess the impact on the carcass prevalence indirectly. The prevalence of Salmonella in carcass swabs among qualifying herds was 0.46% for the 3 years as a whole, with 2006 as the year with highest prevalence. According to the simulation the expected number of human cases relating to pork produced within the programme was below 10. When the programme is in operation, an extra effect of separating pigs within the programme from those outside is expected to lower the prevalence of Salmonella even further.
Australian Food Safety Centre of Excellence, Tasmanian Institute of Agricultural Research, School of Agricultural Science, University of Tasmania, Private Bag 54, Hobart 7001, Tasmania, Australia. firstname.lastname@example.org
Two commercially available organic acid salts, potassium lactate (PURASAL HiPure P) and a potassium lactate-sodium diacetate blend (PURASAL Opti. Form PD 4), were assessed as potential inhibitors of Listeria monocytogenes growth in modified atmosphere packaged (MAP) sliced ham in challenge studies. The influence of the initial inoculation level of L. monocytogenes (10(1) or 10(3) CFU g(-1)) and storage temperature (4 or 8 degrees C) was also examined. The addition of either organic acid salt to MAP sliced ham strongly inhibited the growth of L. monocytogenes during the normal shelf life of the product under ideal refrigeration conditions (4 degrees C) and even under abusive temperature conditions (i.e., 8 degrees C). During the challenge studies and in the absence of either organic acid salt, L. monocytogenes numbers increased by 1000-fold after 20 days at 8 degrees C and 10-fold after 42 days at 4 degrees C. Both organic acid salt treatments were found to be listeriostatic rather than listericidal. The addition of either organic acid salt to the MAP ham also reduced the growth of indigenous microflora, i.e., aerobic microflora and lactic acid bacteria. The influence of these compounds on the risk of listeriosis in relation to product shelf life is discussed.
The data needed for controlling and preventing food-borne infectious diseases relied so far on surveillance of the main food-borne infections (Salmonella and listeria infections) to follow trends over time and detect outbreak. However, this systematic continuous data collection was not always sensitive enough to timely detect community outbreaks and did not take into account sporadic cases of food-borne infections which represent the majority of patients (such as Campylobacter infection for example). Therefore, the true burden of food-borne infections, including morbidity, mortality and the social and economic cost could not be assessed. As the issue of food-borne infections got more social attention, the need of further epidemiological data has increased including the implementation of large population studies (active surveillance and follow up studies) associated with analytical studies in the United States (Foodnet) and in some European countries (United Kingdom, The Netherlands, Denmark.). Meanwhile surveillance and detection of outbreaks have substantially improved through the use of new typing scheme, particularly those based on molecular techniques. Their routine use, now, allows an early identification of the clonal spread of food-borne bacteria. The application of automatic detection algorithm to surveillance data base has also improved the performance of outbreak detection and changes of trends. Furthermore, food-borne infection surveillance has become European which allows, by pooling of national database, to identify emergence that did not get noticed in any country. To foster the prevention of sporadic cases, the use of analytical epidemiology has become more and more frequent and has improved the knowledge of food vehicles and risk factors. The risk assessment approach has also been applied to the microbial contamination of food to answer to the increasing needs of expertise, particularly at the international level. This approach, however, needs further methodological development and the collection of extra information on the food chain. Last, but not the least, a wider public health research approach must also be considered, particularly on the social perception of food-borne risks and the cost-effectiveness analysis of the prevention measures that are taken.
The Danish Salmonella Surveillance and Control Programme for pigs operates at all stages of the production chain and has been applied nationally since 1995. Due to the program the level of Salmonella in Danish pork has declined from 3.5% in 1993 to 0.7% in the year 2000. Simultaneously, the number of human cases with salmonellosis due to pork has declined from approximately 1,144 in 1993 to 166 in 2000. In year 2001, the programme has been improved at a number of stages. A new classification scheme for the serological surveillance of finisher herds has been developed. The individual test cut-off in the mix-ELISA has been reduced to 20 OD%. Only herds producing more than 200 finishers/year are sampled. Based on the serological result from the last 3 months a new weighted salmonella index is calculated: The Danish Bacon and Meat Council has agreed on a new stricter penalty system. Level 2 and 3 herds get a penalty of 2% and 4% of the value per slaughter carcass, respectively. A new method of Salmonella testing on carcasses has been introduced; 5 carcasses per slaughter day are swabbed at 3 defined areas at 100 cm2 for each sample. This method is more sensitive than the one used previously. Herds infected with multiresistant Salmonella Typhimurium DT104 have to follow special restrictions. These include a requirement for a herd intervention plan, restriction on livestock trade, and a requirement for special slurry handling. Carcasses from DT 104 herds must be heat-treated or decontaminated with hot water.
The authors conducted an investigation to determine the extent and source of an outbreak of Salmonella typhimurium gastroenteritis that occurred following a community picnic in Juneau, Alaska, in 1992, and to evaluate risk factors for illness. A case-control study among 54 picnic attendees and a retrospective cohort study among 60 members of 17 households who had taken home leftover food from the picnic were conducted. A case was defined as diarrhea with onset 12-72 hours after eating food that had been prepared for the picnic. The case-control study associated illness with eating roast pork from one of two pigs that had been flown in from a Seattle, Washington, restaurant. The roast pork was taken home by persons from at least the 17 households included in the cohort study. The cohort study identified 43 persons who ate roast pork, of whom 21 (49%) became ill. This compared with only one case of illness among 17 cohort members who had not eaten roast pork (relative risk = 8.3, 95% confidence interval 1.2-57.0). Of 30 persons who ate reheated meat, all 10 who used a microwave oven became ill, compared with none of 20 who used a conventional oven or skillet. The Seattle restaurant had prepared the roast pork by first thawing two frozen pigs for several hours at room temperature and then cooking them in a gas-fired flame broiler. One of the pigs was left unrefrigerated for 17-20 hours after cooking. Compared with conventional methods of reheating, microwave ovens had no protective effect in preventing illness. To prevent outbreaks such as this one, care must be taken to assure that food is both properly cooked and handled and properly reheated.
An ambitious programme to eliminate pork as an important source of human salmonellosis was initiated in Denmark in 1993 by the Ministry of Food, Agriculture and Fisheries. The programme comprises control of feedmills, breeding and multiplying herds, slaughter herds and slaughter plants, as well as the final product, fresh pork. As a consequence, the level of occurrence of Salmonella spp. in fresh pork produced in Denmark is approximately 1%. Yersinia enterocolitica 0:3 infections are common in slaughter pig herds in Denmark, and pork is considered to be the only source of human infection in the country. The incidence of pork-related occurrences of human salmonellosis and yersiniosis in 1996 was approximately nine cases per 100,000 inhabitants for both diseases. All swine in Denmark are screened for Trichinella spp. infection, although no positive results have been obtained since 1930. Swine are not considered to be a source for Campylobacter jejuni or enterohaemorrhagic Escherichia coli in Denmark. Listeria monocytogenes can be detected in relatively high rates in pork: however, the incidence of human listeriosis is only 0.5 cases per 100,000 inhabitants. Toxoplasma gondii antibodies have been demonstrated in 3% of slaughter pigs, though the importance of pork as a source of infection is probably very low. Denmark is officially free from Brucella abortus, B. melitensis and Mycobacterium bovis.
During the years 1983 to 1988, a marked increase in the number of Salmonella infections notified to the Medical Officer of health in Frederiksborg was observed. The epidemiology of Salmonella infections has altered decisively during the past 5-10 years. The number has increased drastically and this increase is due particularly to increase in the number of isolated sporadic cases. The primary cause of the increasing number of infections is increasing contamination of foodstuffs with Salmonella. Improved hygiene in the food industry is essential if the number of infections is to be reduced. Children are frequently infected by direct or indirect contact. Salmonella infections are, therefore, a problem in day institutions and in day care homes. Contact infection may be prevented by improved hygiene and quarantine for children with infectious diarrhoea. Symptom-free excretors, on the other hand, do not present any particular risk for infection and should not be excluded from institutions. Children may excrete bacteria for several months and quarantine based on positive faeces cultures may have considerable social consequences.