An outbreak of salmonella chester infection in Canada: rare serotype, uncommon exposure, and unusual population demographic facilitate rapid identification of food vehicle.
Salmonella Chester infection has rarely been reported in the literature. In 2010, 33 case patients were reported in 2 months in four Canadian provinces. We conducted an outbreak investigation in collaboration with public health agencies, food safety specialists, regulatory agencies, grocery store chains, and the product distributor. We used case patient interviews, customer loyalty cards, and microbiological testing of clinical and food samples to identify nationally distributed head cheese as the food vehicle responsible for the outbreak. The rare serotype, a limited affected demographic group, and an uncommon exposure led to the rapid identification of the source. Control measures were implemented within 9 days of notification of the outbreak.
Based on the data from the integrated Danish Salmonella surveillance in 1999, we developed a mathematical model for quantifying the contribution of each of the major animal-food sources to human salmonellosis. The model was set up to calculate the number of domestic and sporadic cases caused by different Salmonella sero and phage types as a function of the prevalence of these Salmonella types in the animal-food sources and the amount of food source consumed. A multiparameter prior accounting for the presumed but unknown differences between serotypes and food sources with respect to causing human salmonellosis was also included. The joint posterior distribution was estimated by fitting the model to the reported number of domestic and sporadic cases per Salmonella type in a Bayesian framework using Markov Chain Monte Carlo simulation. The number of domestic and sporadic cases was obtained by subtracting the estimated number of travel- and outbreak-associated cases from the total number of reported cases, i.e., the observed data. The most important food sources were found to be table eggs and domestically produced pork comprising 47.1% (95% credibility interval, CI: 43.3-50.8%) and 9% (95% CI: 7.8-10.4%) of the cases, respectively. Taken together, imported foods were estimated to account for 11.8% (95% CI: 5.0-19.0%) of the cases. Other food sources considered had only a minor impact, whereas 25% of the cases could not be associated with any source. This approach of quantifying the contribution of the various sources to human salmonellosis has proved to be a valuable tool in risk management in Denmark and provides an example of how to integrate quantitative risk assessment and zoonotic disease surveillance.
Salmonella Livingstone is occasionally isolated from humans, animals and feedstuffs in Sweden. To follow the spread of infection and trace the source of isolates, adequate typing methods are needed. We have developed an automated typing system based on biochemical fingerprinting of bacteria (the PhP system) for typing of different Salmonella serotypes. The system measures the kinetics of various biochemical reactions of bacteria grown in liquid medium in microtiter plates and uses numerical techniques to identify biochemical phenotypes (BPTs) among the tested strains. In the present study we used a set of 16 highly discriminatory tests to differentiate strains of Salmonella of serotype Livingstone and evaluated the system for its discriminatory ability using a collection of 34 unrelated human isolates of S. Livingstone. We also used the system to investigate BPTs of 45 Livingstone strains isolated from animals and feedstuffs in Sweden between 1987 and 1991. Altogether 19 different BPTs were found among human isolate giving a diversity index (Di) of 0.930. In contrast, most strains isolated from animals and feedstuffs in Sweden belonged to 2 dominating BPTs (Di = 0.704). One of these contained 17 strains mainly isolated during 1992 whereas the other contained 18 strains isolated between 1987 and 1991. None of the Swedish human isolates were identical to those of animals and feedstuffs. These findings suggest that 2 different BPTs of Salmonella Livingstone strains are particularly common among animals and feedstuffs in Sweden and that they are not related to human cases of enteritis in this country. We also conclude that biochemical fingerprinting with the PhP system is a reliable and highly discriminatory method for detecting epidemic strains of Salmonella Livingstone.
The goal of the study was to examine if intake of Lactobacillus plantarum can accelerate clearance of nontyphoid Salmonella and reduce infection-related symptoms.
Nontyphoid Salmonella is a major cause of gastroenteritis worldwide. Few studies have explored the effect of probiotics in these infections.
Patients with Salmonella infection were randomized to daily intake of 5 × 10 colony forming units of freeze-dried Lactobacillus plantarum 299 v or placebo. Symptoms were recorded daily. Feces were cultured weekly. Treatment continued until 4 consecutive stool cultures negative for Salmonella had been obtained.
The treatment and placebo groups did not differ significantly with regard to time to clearance of Salmonella, or time to resolution of symptoms. Irrespective of treatment, women tended to clear Salmonella more rapidly than men (19 vs. 28 d, P=0.18), despite a longer diarrheal phase (5 vs. 3 days after inclusion, P=0.001). After Salmonella clearance (postinfectious phase), women experienced loose stools, nausea, and flatulence more frequently than men. In women, L. plantarum treatment was associated with more abdominal pain, whereas in men L. plantarum treatment reduced the prevalence of hard stools, and increased the presence of diarrheal symptoms in the postinfectious phase.
Gender, but not administration of the probiotic strain L. plantarum 299 v, may influence acute symptoms during Salmonella infection and possibly clearance of Salmonella. Symptoms in the postinfectious phase were modified by the probiotics in a gender-specific way, but our results give little support for positive effects of L. plantarum 299 v treatment in nontyphoid salmonellosis.
Surveillance and control are important aspects of food safety assurance strategies at the pre-harvest level of pork production. Prior to implementation of a Salmonella surveillance and control programme, it is important to have knowledge on the dynamics and epidemiology of Salmonella infections in pig herds. For this purpose, 17 finishing pig herds initially classified as seropositive and 15 as seronegative, were followed for a 2-year period through serological and bacteriological sampling. The study included 10 herds from Denmark, 13 from The Netherlands, 4 from Germany and 5 from Sweden and was performed between October 1996 and May 1999. The Salmonella status of finishing pig herds was determined by an initial blood sampling of approximately 50 finishing pigs close to market weight per herd. The development of the Salmonella status of the selected herds was assessed at seven subsequent sampling rounds of 25 blood samples from finishing pigs, 25 blood samples from grower pigs and 10 pen faecal samples each, approximately 3 months apart. The odds for testing finishers seropositive, given that growers were found seropositive previously were 10 times higher than if growers were seronegative (OR 10.0, 95% CI 3.2-32.8). When Salmonella was isolated from pen faecal samples, the herd was more likely to be classified seropositive in the same sampling round, compared to no Salmonella being detected (OR 4.0, 95% CI 1.1-14.6). The stability of an initially allocated Salmonella status was found to vary noticeably with time, apparently irrespective of a seropositive or seronegative classification at onset of the study. Given the measured dynamics in the occurrence of Salmonella in pig herds, regular testing is necessary to enable producers, advisors and authorities to react to sudden increases in the Salmonella prevalence in single herds or at a national level.
The purpose of this study was to determine pet-related management factors that may be associated with the presence of Salmonella spp. in feces of pet dogs from volunteer households. From October 2005 until May 2006, 138 dogs from 84 households in Ontario were recruited to participate in a cross-sectional study. Five consecutive daily fecal samples were collected from each dog and enrichment culture for Salmonella spp. was performed. A higher than expected number of the dogs (23.2%; 32/138) had at least one fecal sample positive for Salmonella, and 25% (21/84) of the households had at least one dog shedding Salmonella. Twelve serotypes of Salmonella enterica subsp. enterica were identified, with the predominant serotypes being Typhimurium (33.3%; 13/39), Kentucky (15.4%; 6/39), Brandenburg (15.4%; 6/39) and Heidelberg (12.8%; 5/39). Univariable logistic regression models were created with a random effect for household to account for clustering. Statistically significant risk factors for a dog testing positive included having contact with livestock, receiving a probiotic in the previous 30 days, feeding a commercial or homemade raw food diet, feeding raw meat and eggs, feeding a homemade cooked diet, and having more than one dog in the household. In two-variable models that controlled for feeding raw food, the non-dietary variables were no longer statistically significant. These results highlight the potential public health risk of including raw animal products in canine diets.
The relationship between invasiveness and incidence of non-typhoid salmonellosis was ascertained retrospectively in a population of 1.9 million in four Danish counties during the three-year period 1992-1994. The study comprised 4175 cases diagnosed by culture either locally or at Statens Serum Institut, Copenhagen. Two hundred and forty-four patients had extraintestinal infections caused by 24 out of the total number of 101 different serotypes. Invasiveness ranged widely from 4% to > 90% for individual serotypes. Salmonella typhimurium and Salmonella enteritidis formed a high-incidence group (incidence rates > or = 25/100,000/year) compared to the remaining 22 serotypes (
From the Centers for Disease Control and Prevention. Outbreak of Salmonella serotype Muenchen infections associated with unpasteurized orange juice--United States and Canada, June 1999.
