Isolation of mini-Tn5Km2 insertion mutants of Salmonella enterica serovar Oranienburg sensitive to NaCl-induced osmotic stress

We previously reported that the viability of Salmonella Oranienburg strains under NaCl stress was variable and depended on the strain's origin; food strains were resistant and patient strains sensitive to NaCl. Therefore, we mutagenized a food strain with a mini-Tn5Km2 transposon. Of 2,400 mutants screened, 15 NaCl-sensitive mutants were isolated, and 7 genes associated with NaCl-sensitivity were identified. The intact genes complemented their own food-strain mutants, but not patient-strain mutants, suggesting that the difference in NaCl-sensitivity between food and patient S. Oranienburg strains might not arise from a single gene mutation, but from change in multiple osmoregulatory mechanisms in Salmonella.

Outbreak of a new Salmonella phage type in South West England: alternative epidemiological investigations are needed

An outbreak of Salmonella Typhimurium DT193a occurred in South West England in April-May 2003. Preliminary investigation suggested an association with the consumption of ham. A matched case-control study was implemented, together with an environmental investigation and a geographic information system (GIS) analysis. Thirty-seven cases and 38 controls were enrolled in the study. Matched analysis was based only on 23 cases, as the other cases did not nominate controls. Eighty per cent of cases and 51% of controls had eaten ham (odds ratio = 3.5, p = 0.03). Cases did not differ from controls in terms of distance from outlets providing ham. All environmental samples collected were negative. The epidemiological evidence indicated an association between this outbreak and consumption of ham, but the environmental investigation was inconclusive. Alternative methods should be considered in support of traditional epidemiological investigation.

Prolonged incubation period of salmonellosis associated with low bacterial doses

In gastroenteritis outbreaks caused by Salmonella-contaminated lunches at elementary, junior high, and nursery schools. outbreaks with long median incubation periods (i.e., 60 to 120 h) were observed frequently between 1990 and 1999 in Japan. We analyzed epidemiological data on 185 outbreaks of Salmonella Enteritidis infection to study the factors underlying the long incubation period. These survey results showed that the median incubation period for Salmonella Enteritidis infection from contaminated school and nursery school lunches was significantly longer than that from other types of cooking facilities. In addition, we analyzed the relationship between the median incubation period and the bacterial dose ingested per person in nine outbreaks of Salmonella Enteritidis infection; the bacterial dose was estimated with reference to the bacterial concentration in the causative foods. A significant negative correlation between the bacterial dose ingested per person and the median incubation period is clearly shown. The time elapsed from the start of the cooking process to the consumption of school and nursery school lunches was significantly shorter than at other cooking facilities, suggesting limited bacterial growth, which in turn is thought to lead to a long incubation period.

[Epidemiological analysis of Salmonella enteritidis isolates using pulsed-field gel electrophoresis and bacteriophage typing over the period of April 2000 to March 2003 in Gifu Prefecture]

We examined a total of 151 Salmonella enterica serovar Enteritidis strains isolated in Gifu Prefecture during the period from April 2000 to March 2003 by using bacteriophage typing and pulsed-field gel electrophoresis (PFGE). Bacteriophage typing classified them into twelve phage types (PT) and RDNC (reacted but did not conform). The predominant phage type was PT47 (34.4%) followed by PT1 (21.9%), PT4 (16.6%) and RDNC (11.3%). XbaI- and BlnI-digested PFGE analyses identified 17 and 44 PFGE patterns, respectively, indicating that PFGE with BlnI had more discriminating power than that with XbaI. Combination of the phage types and PFGE types of BlnI could make 53 subtypes. Some isolates with the same phage type were subdivided into different PFGE types, but those with PT47 were not. PT47 isolates were derived from sporadic patients with gastroenteritis, food poisoning outbreaks and healthy carriers through the years. This suggests that PT47 is highly clonal and disseminates over our prefecture.

Salmonella Enteritidis in Bosnia and Herzegovina

A comprehensive retrospective analysis of human Salmonella Enteritidis isolates in the Zenica-Doboj Canton of Bosnia and Herzegovina was conducted by inquiry and questionnaire. In the period 1998-2000, 299 isolates of Salmonella spp. were recorded, of which S. Enteritidis accounted for 74.2%. The isolation rate of S. Enteritidis increased during this period, from 12.7 to 25.5 isolates/year/100,000 population. Isolates were obtained all year round, mostly from sporadic cases of infection or limited family outbreaks. Home-made food was identified as the most important source of infection, being implicated in 81% of outbreaks and 81.7% of cases of sporadic infection.

Long-term post-Salmonella reactive arthritis due to Salmonella Blockley

We describe the case of a patient who became ill with Salmonella Blockley food poisoning while working in Cyprus in August 1994. As his diarrhoea resolved he began to suffer from lower limb joint pains which were diagnosed as acute salmonella reactive arthritis. His condition deteriorated, then improved somewhat over a period of 2 years, but he continued to suffer symptoms over 5 years after infection. This case predates other reported cases of S. Blockley infection in Cyprus by 4 years. S. Blockley is associated with chickens, and the chicken meal is the probable source of his infection. This case is of interest since it demonstrates the emergence of the serovar outside South East Asia where it is common, and shows that information on the incidence and duration of reactive arthritis caused by serovars other than S. Enteritidis and S. Typhimurium is limited.

Prolonged restaurant-associated outbreak of multidrug-resistant Salmonella Typhimurium among patients from several European countries

This report concerns a prolonged restaurant-associated outbreak of infection caused by a multidrug-resistant (ASSuT) strain of Salmonella Typhimurium, phage-type U302, which took place during July and August 2003 and affected people from Denmark and neighbouring countries who had attended a specific restaurant. The outbreak comprised 67 laboratory-verified cases and ten probable cases; however, the actual number of patients was estimated to be more than 390. The outbreak strain was isolated from a buffet which was probably contaminated by an assistant chef who was found to excrete the epidemic strain. An attack rate of 7.3% was estimated and long incubation periods were observed, including one extreme instance of 27 days. This outbreak underscores the importance of conscientious personal hygiene, including frequent washing of hands, for professionals handling food.

Occurrence of Salmonella Enteritidis phage type 29 in Austria: an opportunity to assess the relevance of chicken meat as source of human Salmonella infections

Assuming that the various phage types of Salmonella Enteritidis (S. Enteritidis) are largely equally virulent, the importance of certain foods as sources of infection for human salmonellosis can be deduced from differences in the distribution of phage types in human and non-human samples. In 2002, S. Enteritidis phage type 29 (PT29) was first isolated from non-human test samples in Austria. S. Enteritidis PT29 accounted for 44 (27.7%) of 159 S. Enteritidis strains, derived from veterinary samples of chicken (e.g. meat, giblets) or chicken habitations (e.g. swabs from the coop and excrement). At the food retail level (chicken meat, chicken liver), five (13.1%) of 38 S. Enteritidis isolates were PT29. The proportion of S. Enteritidis PT29 in human samples was much lower. Only 0.4% (30 human primary isolates) of all S. Enteritidis isolates in the year 2002, and 0.33% (23 human primary isolates) of all human S. Enteritidis strains in 2003 were PT29. In our opinion, the discrepancy between the high prevalence of S. Enteritidis PT29 in broilers and chicken meat and the low number of PT29 cases in humans indicates that chicken meat of Austrian origin is currently only a minor source of human S. Enteritidis infections.

A foodborne outbreak of Salmonella enterica subsp. enterica serovar Madelia at a silver anniversary reception

Reported here is an outbreak of Salmonella enterica subsp. enterica serovar Madelia infection that occurred among 44 persons attending a silver anniversary reception in Hesse, Germany. Isolates of Salmonella Madelia are extremely unusual, and no outbreaks associated with this serotype have been reported previously. Forty-two attendees were interviewed and information was obtained from each of them regarding demographic and clinical characteristics and food consumed at the reception. Twenty-four attendees submitted stool samples for microbiological testing, and 10 of these were culture-positive for S. Madelia. Twenty-three attendees met the case definition of infection, while 18 met the clinical case definition (i.e. vomiting or diarrhoea within 3 days of consuming food at the reception) and five had asymptomatic infection with S. Madelia. The most likely vehicles of infection were tortellini and a red pesto sauce.

An outbreak due to peanuts in their shell caused by Salmonella enterica serotypes Stanley and Newport--sharing molecular information to solve international outbreaks

Salmonellosis is a global problem caused by the international movement of foods and high incidence in exporting countries. In September 2001, in an outbreak investigation Australia isolated Salmonella Stanley from imported peanuts, which resulted in a wider investigation in Canada, England & Wales and Scotland. Patients infected with Salmonella serotypes known to be isolated from peanuts and reported to surveillance systems were interviewed to determine exposure histories. Tagged image file format (TIFF) images of pulsed-field gel electrophoresis (PFGE) patterns of Salmonella isolates were shared electronically amongst laboratories. Laboratories tested packets of 'Brand X' peanuts from various lots and product lines. In total, 97 cases of S. Stanley and 12 cases of S. Newport infection were found. Seventy-three per cent (71/97) of S. Stanley cases were in persons of Asian ethnicity. Twenty-eight per cent of cases recalled eating Brand X peanuts and a further 13% had peanuts in their house in the previous month or had eaten Asian-style peanuts. Laboratories isolated S. Stanley, S. Newport, S. Kottbus, S. Lexington and S. Unnamed from Brand X peanuts. Isolates of S. Stanley from peanuts and human patients were indistinguishable by PFGE. This international outbreak resulted from a product originating from one country affecting several others. Rapid sharing of electronic DNA images was a crucial factor in delineating the outbreak; multinational investigations would benefit from a harmonized approach.

Multidrug-resistant Salmonella Typhimurium infection from milk contaminated after pasteurization

An outbreak of multidrug-resistant Salmonellaenterica serotype Typhimurium infections occurred in Pennsylvania and New Jersey. A case-control study implicated pasteurized milk from a dairy, and an inspection indicated the potential for contamination after pasteurization. Dairy cattle are the likely reservoir, and milk may be an important vehicle of Salmonella transmission to humans.

Pulsed-field electrophoretic fingerprinting of Salmonella indiana and its epidemiological applicability

Eight Xba I-generated pulsed-field profile (PFP) types and four subtypes within one of the most common PFP types have been identified in Salmonella indiana from patients, poultry and human food in England and Wales in the three-year period from January 1994 to December 1996. Two PFP types have predominated, PFP X1 and PFP X2. Although the PFP X1 type was identified throughout the study period, the PFP X2 type was not identified until late 1995, subsequently becoming the most common PFP type in humans in the first six months of 1996 with a significant distribution in elderly patients. It is concluded that PFGE can be used in support of epidemiological investigations for the subdivision of Salm. indiana. Furthermore, as both conditions and interpretation criteria can be easily standardized, it is suggested that for many salmonella serotypes, PFGE can provide the basis for a definitive scheme of genotypic subtyping suitable for epidemiological investigations at both a national and international level.

Serological characterization and prevalence of spvR genes in Salmonella isolated from foods involved in outbreaks in Brazil

Salmonella strains (n = 75) isolated from foods involved in foodborne outbreaks occurred in Rio Grande do Sul State, Brazil, during 1999 and 2000 were studied. Strains were serotyped and submitted to PCR analysis to verify the prevalence of Salmonella plasmid virulence (spvR) regulatory gene. Among the 75 isolates, 73 (97%) were classified as Salmonella enterica serovar Enteritidis. All of the Salmonella strains isolated in 1999 were classified as serotype Enteritidis, whereas in 2000 two isolates were serotyped as Salmonella Derby and Salmonella Typhimurium. Regarding the prevalence of spvR gene, 62 strains (82.7%) were PCR positive, and a positive correlation (P < 0.05) between the strains of Salmonella Enteritidis and the presence of spvR gene was demonstrated, which suggests that this gene is a characteristic of the Salmonella Enteritidis analyzed.

A quantitative risk assessment model for Salmonella and whole chickens

Existing data and predictive models were used to define the input settings of a previously developed but modified quantitative risk assessment model (QRAM) for Salmonella and whole chickens. The QRAM was constructed in an Excel spreadsheet and was simulated using @Risk. The retail-to-table pathway was modeled as a series of unit operations and associated pathogen events that included initial contamination at retail, growth during consumer transport, thermal inactivation during cooking, cross-contamination during serving, and dose response after consumption. Published data as well as predictive models for growth and thermal inactivation of Salmonella were used to establish input settings. Noncontaminated chickens were simulated so that the QRAM could predict changes in the incidence of Salmonella contamination. The incidence of Salmonella contamination changed from 30% at retail to 0.16% after cooking to 4% at consumption. Salmonella growth on chickens during consumer transport was the only pathogen event that did not impact the risk of salmonellosis. For the scenario simulated, the QRAM predicted 0.44 cases of salmonellosis per 100,000 consumers, which was consistent with recent epidemiological data that indicate a rate of 0.66-0.88 cases of salmonellosis per 100,000 consumers of chicken. Although the QRAM was in agreement with the epidemiological data, surrogate data and models were used, assumptions were made, and potentially important unit operations and pathogen events were not included because of data gaps and thus, further refinement of the QRAM is needed.

Discerning strain effects in microbial dose-response data

In order to estimate the risk or probability of adverse events in risk assessment, it is necessary to identify the important variables that contribute to the risk and provide descriptions of distributions of these variables for well-defined populations. One component of modeling dose response that can create uncertainty is the inherent genetic variability among pathogenic bacteria. For many microbial risk assessments, the "default" assumption used for dose response does not account for strain or serotype variability in pathogenicity and virulence, other than perhaps, recognizing the existence of avirulent strains. However, an examination of data sets from human clinical trials in which Salmonella spp. and Campylobacter jejuni strains were administered reveals significant strain differences. This article discusses the evidence for strain variability and concludes that more biologically based alternatives are necessary to replace the default assumptions commonly used in microbial risk assessment, specifically regarding strain variability.

Changes in Salmonella enterica serovar Oranienburg viability caused by NaCl-induced osmotic stress is related to DNA relaxation by the H-NS protein during host infection

The NaCl sensitivity of Salmonella enterica serovar Oranienburg strains depends on their origin. We found previously that food- and patient-origin isolates in an outbreak were, respectively, NaCl-resistant and NaCl-sensitive, and the NaCl-resistant strain of food-origin isolates became NaCl-sensitive after passage of the strain through mice [FEMS Microbiol. Lett. 212 (2002) 87]. Here, we report that this phenotypic difference is mainly dependent on topological changes regulated by H-NS, a bacterial histone-like nucleoid protein that binds non-specifically to DNA. That is, this phenotypic difference was caused by changes in DNA topology during infection of the host. Based on these findings, we propose this mechanism has a key role in promoting the survival of Salmonella under osmotic stress.

Dose-response model for 13 strains of salmonella

Data from a human feeding trial with healthy men were used to develop a dose-response model for 13 strains of Salmonella and to determine the effects of strain variation on the shape of the dose-response curve. Dose-response data for individual strains were fit to a three-phase linear model to determine minimum, median, and maximum illness doses, which were used to define Pert distributions in a computer simulation model. Pert distributions for illness dose of individual strains were combined in an Excel spreadsheet using a discrete distribution to model strain prevalence. In addition, a discrete distribution was used to model dose groups and thus create a model that simulated human feeding trials. During simulation of the model with @Risk, an illness dose and a dose consumed were randomly assigned to each consumption event in the simulated feeding trial and if the illness dose was greater than the dose consumed then the model predicted no illness, otherwise the model predicted that an illness would occur. To verify the dose-response model predictions, the original feeding trial was simulated. The dose-response model predicted a median of 69 (range of 43-101) illnesses compared to 74 in the original trial. Thus, its predictions were in agreement with the data used to develop it. However, predictions of the model are only valid for eggnog, healthy men, and the strains and doses of Salmonella used to develop it. When multiple strains of Salmonella were simulated together, the predicted dose-response curves were irregular in shape. Thus, the sigmoid shape of dose-response curves in feeding trials with one strain of Salmonella may not accurately reflect dose response in naturally contaminated food where multiple strains may be present.

Cephalosporin-resistant Escherichia coli among summer camp attendees with salmonellosis

Investigation of an acute gastroenteritis outbreak involving >100 persons at a summer camp in Girona, Spain, in June 2002 led to the detection of Salmonella and extended-spectrum cephalosporin-resistant Escherichia coli (ESCREC). Stool cultures were performed for 22 symptomatic campers, three asymptomatic food handlers, and 10 healthy household members. Of the 22 campers, 19 had Salmonella enterica, 9 had an ESCREC strain carrying an extended-spectrum β-lactamase, and 2 had a second ESCREC strain carrying a plasmidic cephamycinase. Related ESCREC were detected in two (salmonella-negative) asymptomatic food handlers and in none of the healthy household members. Fecal ESCREC and its β-lactamases and plasmids were extensively characterized. Three of the five ESCREC clones were recovered from multiple hosts. The apparent dissemination of ESCREC suggests a food or water vehicle. The observed distribution of resistance plasmids and β-lactamase genes in several clones indicates a high degree of horizontal transfer. Heightened vigilance and increased efforts must be made to discover the reservoirs and vehicles for community dissemination of ESCREC.

The detection and determination of potential virulence of Salmonella spp. using PCR method

The aim of this study was to prove that PCR is a very useful method to identify Salmonella strains and to determine their virulence factors by amplification of characteristic genetic markers. Investigations included 5 strains of Salmonella which were obtained from pure cultures and 1 Salmonella strain from the mixed culture. Genotypic analysis of 6 examined strains revealed the 163-bp fragment of chromosomal DNA, which is the DNA rep. ori. gene, encoding the particular genus. In all of these strains 215-bp, 203-bp and 204-bp chromosomal DNA fragments were identified as representing the stn, stpA and spaO genes that confirmed their virulence. These amplification products were identified in both pure and mixed culture from pork. Sensitive and rapid PCR method may be used not only for identification of Salmonella strains and for determination of their virulence factors but also for routine microbiological diagnostic of food pathogens.

[Surveillance of foodborne diseases in the province of Rio Negro, Argentina, 1993-2001]

A total of 39 outbreaks of foodborne diseases affecting 958 people in the province of Rio Negro, Argentina between 1993 and 2001 are described and evaluated. The main causal agents were identified involving food, sites of occurrence, risk factors and notification system used. Salmonella spp (38%), Trichinella spiralis (15%), Escherichia coli (13%) and Staphylococcus aureus (15%) were the most frequent agents present in outbreaks. Salmonella spp produced the largest number of cases (52%). Food involved were cooked meat (36%), cheese (10%), sandwiches (10%), deserts (10%) and ice cream (8%). Indeed, ice creams were involved in the largest number of cases and of people affected. In relation to the source of food, 41% of outbreaks were caused by homemade meals, 23% by catering or ice cream parlor, 13% in family parties, 8% in county fairs and 8% in hotel restaurants. In 28% of the outbreaks the etiological agent was identified exclusively by epidemiological analysis, in 64% isolation of the agent was carried out, and in 8% of the cases, a final diagnosis could not be obtained. Validity of epidemiological studies in foodborne disease, the necessity of strengthening the notification system of outbreaks, and the importance of good practices in food handling are analyzed.

Epidemiological and epizootological aspects of salmonellosis

In their case report, most of the patients with salmonellosis mentioned consumption of meals containing poultry products, primarily eggs and egg products as a source of their disease. Microbiological analysis of samples showed that in more than 88 % of cases the infection agent was identified as Salmonella enteritidis. This serovar is the most frequent pathogen isolated at poultry farms. In the period of the past five years, 171 outbreaks of salmonellosis were recorded in Slovakia. However, within the group of animal tenders at these farms, no case of salmonellosis was confirmed. The alimentary character of salmonellosis led us to check results of analyses of samples of food and foodstuff of animal origin examined for Salmonella spp. performed during the past five years. The control of results indicated that out of these 228 545 samples of food and foodstuff of animal origin only 0.21% were confirmed as being Salmonella positive and the average ratio of Salmonella enteritidis occurrence in samples was 0.1% per year. A higher incidence (1.43 %) was recorded only in eggs and egg products. Our observations indicated that there was a change in tenacity of Salmonella enteritidis due to its increased resistance, primarily against elevated temperatures including that of pasteurization. An everyday requirement for decreasing the incidence of salmonellosis is based on strict hygienic behaviour "from stable to table". The objective of salmonellosis elimination strongly depends on amending the current legislation as to the establishment of hygienic conditions in complete food chains. (Tab. 4, Ref. 21.)

Outbreaks of food borne diseases in the Lazio region, Italy: the results of epidemiological field investigations

BACKGROUND

More thorough information about risks, exposures and vehicles of food borne diseases can be obtained from epidemiological field investigations than from infectious disease reports or laboratory data.

METHODS

We analysed the results of 410 field investigations of food borne disease outbreaks reported from 1996 to 2000 and conducted as cohort studies.

RESULTS

The incidence of food borne outbreaks increased from 0.8/100,000 in 1996 to 2.0 in 1999, as did the incidence of salmonellosis (from 16/100,000 to 21 in the same period) and diarrhoea episodes reported by laboratories (from 12/100,000 in 1997 to 29 in 1999). Of the food borne disease outbreaks, 264 (64.4%) occurred in private homes; 5 (1.2%) in hospitals; 31 (7.6%) in canteens and refectories, 84 (20.5%) in restaurants, 41 of which occurred during special functions. The home outbreaks exposed few people (average of 7), had high attack rates (61.7% average) and a high proportion of known aetiology (66%), while food borne disease outbreaks in canteens and restaurants (during special functions) exposed many people (300 and 81, respectively), had medium attack rates (19.7 and 34.5%, respectively) and a higher proportion of confirmed vehicles (50 and 49%, respectively), compared to those occurring at home (21%). Salmonella spp. was the most frequent agent detected in each setting (67% of confirmed cases). The most frequent vehicles at home were mushrooms and sweets containing eggs and cream; in canteens, meat and vegetables and in restaurants, shellfish.

CONCLUSIONS

Outbreak characteristics varied according to the setting. This implies the need for a different approach of field investigations, and different preventive measures.

[Typing of Salmonella by DNA-microarrays]

Microarrays (DNA-Chips) are miniaturized carriers on which many nucleic acid molecule probes such as oligonucleotides or PCR products are immobilized in a high density, and compactness. Homologue DNA hybridises with the immobilized complementary nucleic acid probes. This study gives after a short general introduction in the principle of DNA-microarrays an overview about published data on the field of typing of Salmonella by microarrays. An onset of a DNA-microarray developed by the National Reference Laboratory for Salmonella (NRL-Salm) will be introduced. By this new technique, it is possible to answer epidemiological questions as well as to find genes involved in certain biochemical processes, such as pathogenicity or resistance of salmonellae.

A case of retroperitoneal abscess caused by Salmonella Oranienburg

The authors report a case of retroperitoneal abscess caused by Salmonella Oranienburg in an 8-year-old girl. This was one case in an epidemic of food poisoning from Salmonella Oranienburg or Salmonella Chester transmitted by many kinds of contaminated dried squid products. This is the first reported case of a retroperitoneal abscess by Salmonella Oranienburg.

Occurrence of Salmonella enterica serovar Dublin in Austria

In Austria, Salmonella enterica serovar Dublin, a bovine-adapted serovar, rarely causes human infections. In the year 2000, Austria was within the European mean with an incidence of 0.1 per million inhabitants. Our data show that the vast majority of all Austrian serovar Dublin infections can be traced to two Tyrolian districts. This concentration of cases can be explained by a particularly traditional aspect of cattle farming in Tyrol, the alpine pasture. There is increased risk of cross-infection due to the communal keeping of animals from various farms. Infected cattle are a source of infection for people, and contagion usually occurs from eating beef and drinking cow's milk. Using pulsed-field gel electrophoresis and automated ribotyping, 3 out of 5 available isolates from human infections could be traced to characteristic Tyrolian S. Dublin clones. Bacteriological screening of herds with a known history of S. Dublin infection would be a start to prevent future contamination of alpine pastures through latently infected cattle excreting potentially infectious feces. Bacteriological screening for fecal carriage before the return of cattle from pastures known to be connected with infections could prevent cross-contamination of large mixed herds.

A regional outbreak of S. Enteritidis phage type 5, traced back to the flocks of an egg producer, Austria

In the spring and summer of 2002, the Nationale Referenzzentrale für Salmonellen (National Reference Centre for Salmonella - NRCS) in Austria noticed a cluster of human Salmonella enterica subsp. enterica ser. Enteritidis phage type 5 (S. Enteritidis PT5) infections in two neighbouring districts of Austria. Another small outbreak of S. Enteritidis PT5 infections that occurred in the same region in 1999 had been traced back to the flocks of a local egg producer (approximately 6 000 hens). Attention was therefore again directed at this farm. The results of voluntary bacteriological examinations from the farm and further epidemiological investigations identified the same egg producer as the source of the second outbreak. The 70 human isolates of S. Enteritidis PT5 ascertained in 2002 represented a minority of all infections. It is realistic to estimate that several hundred infections occurred in the course of the 2002 outbreak. The farmer had not vaccinated new flocks against Salmonella since August 2001. It is likely that the change in vaccination policy resulted in the reappearance of the S. Enteritidis PT5 infections. By the end of September 2002 the farmer had stopped selling untreated table eggs. In October 2002 only one isolate of S. Enteritidis PT5 was ascertained in the region.

Application of an automated immunomagnetic separation-enzyme immunoassay for the detection of Salmonella spp during an outbreak associated with a retail premises

AIMS

The application of an automated immunomagnetic separation-enzyme immunoassay (AIMS-EIA) during the investigation of a suspected outbreak of Salmonella food poisoning at a retail premises.

METHODS AND RESULTS

Six food samples and 24 environmental swabs were taken from the retail premises and six food handlers' submitted faecal samples during the investigation of the outbreak. Isolation and identification of Salmonella from these samples was performed according to established standard operating procedures and by AIMS-EIA. Twelve of the 18 (67%) Salmonella culture positive samples were AIMS-EIA positive on testing pre-enrichment samples after 24 h, whilst 17 (94%) samples were AIMS-EIA positive following selective enrichment for a further 48 h. One food handler was found to be positive for Salmonella by both culture and AIMS-EIA. All Salmonella isolates were confirmed as Salmonella Enteritidis phagetype 21c.

CONCLUSIONS

The AIMS-EIA protocol compliments the conventional culture approach to produce more timely results for the management of the risk to public health without significantly increasing the workload of the laboratory.

SIGNIFICANCE AND IMPACT OF THE STUDY

The food production premise investigated in this study was heavily contaminated with Salmonella Enteritidis. Application of the AIMS-EIA was significant in the effective intervention of control measures for the protection of public health.

Phage-based typing scheme for Salmonella enterica serovar Heidelberg, a causative agent of food poisonings in Canada

Salmonella enterica serovar Heidelberg is perhaps the second most frequent Salmonella serovar isolated from humans and the most common isolated from animals in Canada. This pathogen has shown increasing resistance to antimicrobial agents and mimics the multidrug resistance observed in S. enterica serovar Typhimurium strain DT 104. However, unlike for serovar Typhimurium, a rapid and inexpensive subtyping method has not been available for large-scale surveillance efforts. We developed a phage typing scheme and subtyped 2,523 strains of serovar Heidelberg from outbreaks, sporadic infections, and environmental sources in Canada between January 1991 and December 2000. All strains were sensitive to one or more phages and could be subdivided into 49 phage types. A total of 196 isolates from 13 major outbreaks could be subtyped into six phage types, while 86 strains from family outbreaks were assigned to seven phage types. All strains were typeable, and epidemiologically related strains isolated from patients and implicated foods had identical phage types, antibiograms, and pulsed-field gel electrophoresis (PFGE) patterns. Combining PFGE with phage typing increased the discriminatory power of the analysis beyond that of either method alone. We concluded that this phage typing scheme, in conjunction with PFGE, enhances subtyping of serovar Heidelberg strains. Furthermore, this phage typing scheme is a rapid, economical, stable, and reliable epidemiologic tool for tracing the origin of food-borne disease and for the surveillance of sporadic infections.

Usefulness of different techniques in the study of the epidemiology of salmonellosis

Our objective was to evaluate the usefulness of serotyping, phagotyping, antibiotyping and RAPD (random amplified polymorphic DNA) in the study of the epidemiology of salmonellosis in Elche (Spain). We examined 1232 clinical isolates of non-typhoid Salmonella serotypes. Serotyping adequately differentiates 12.3% of the isolates and phagotyping raises this percentage to 37%. Antibiotyping is a suitable complement in certain circumstances, such as in the case of specific outbreaks. RAPD is a fast and simple technique which is within the reach of most laboratories, complementing the results obtained by antibiotyping and serotyping, in order to be able to control outbreaks of salmonellosis in everyday practice.

Evaluation of selective and non-selective enrichment PCR procedures for Salmonella detection

AIMS

To compare PCR combined with enrichment media with the standard microbiological techniques (SMT) and to determine the most sensitive method for the detection of Salmonella and the identification of Salm. typhimurium (ST), Salm. enteritidis (SE), Salm. gallinarum (SG) and Salm. pullorum (SP).

METHODS AND RESULTS

We analysed 87 samples from poultry using PCR and SMT, PCR being performed from non-selective (NS) and Rappaport-Vassiliadis (RV) media. PCR-NS was less sensitive than PCR-RV and SMT for the detection and identification of Salmonella. PCR-RV detected more positive samples of Salmonella sp. than SMT but both these methods showed similar sensitivity regarding the identification of Salmonella serovars.

CONCLUSIONS

PCR-RV was more sensitive and decreased the time necessary to detect and identify Salmonella.

SIGNIFICANCE AND IMPACT OF THE STUDY

PCR-RV is a powerful tool for the rapid and accurate detection and identification of Salmonella and can be implemented in diagnostic and food analysis laboratories.

Detection of a nosocomial outbreak of salmonellosis may be delayed by application of a protocol for rejection of stool cultures

In October 2001 an outbreak of Salmonella enterica serovar enteritidis phage-type 6 occurred in a hospital and a nursing home, both served by the same hospital kitchen. Five nursing home residents died during the outbreak. S. enteritidis was isolated from three of them. Of 231 stool samples from nursing home residents, hospital patients and employees, 82 were culture-positive. All symptomatic patients were treated with oral ciprofloxacin. Inspection of the kitchen showed that during preparation of the desserts implicated in causing the outbreak, temperatures were not measured and storage temperatures were too high. No left-over food samples were available for analysis. According to the 'four-day rule' in use in this hospital, the stool samples related to the first outbreak were not cultured for Salmonella spp., whereas culturing afterwards from both stored specimens and repeats, showed that some of these samples would have been positive for S. enteritidis. Thus without the application of stool culture rejection criteria the outbreak would have been detected one day earlier. With the four-day rule in effect, the outbreak might have been detected much later, if an unusually high number of nursing home residents with gastroenteritis had not been noticed by nursing home physicians. The rule was revised to prevent a possible delay in the future. As a result of this outbreak, the government has announced legislation forbidding the sale of Salmonella-contaminated eggs. An official ban on the use of raw eggs will be included in several hygiene codes.

Quantitative risk assessment of human salmonellosis from the consumption of a turkey product in collective catering establishments

The quantitative risk assessment (QRA) approach recommended by the Codex Alimentarius Commission was used to assess the risk of human salmonellosis from the consumption of 'cordon bleu', a specific turkey product, in collective catering establishments (CCEs) of a French department. The complete process was modeled and simulated, from the initial storage in the CCE freezer to the consumption, using a Monte Carlo simulation software. Data concerning the prevalence of contaminated 'cordon bleu', the level of contamination of Salmonella, the cooking and storage process were collected from 21 CCEs and 8 retailers of 'cordon bleu' in the selected department. Thermal inactivation kinetics for Salmonella were established to estimate the effect of heat treatment on the concentration in the product and to calculate the dose that could be ingested by the consumer. The Beta-Poisson dose-response model of Rose and Gerba [Water Science and Technology 24 (1991) 29] with the specific parameters for Salmonella was used to estimate the probability of infection related to the ingestion of a particular dose and a factor was applied to estimate the probability of illness from ingestion. The individual risk of salmonellosis, the risk of outbreak and the number of cases were calculated using Monte Carlo simulation method. The risk of salmonellosis was close to zero when the 'cordons bleus' were cooked in the oven. Therefore, the risk was calculated for the fryer cooking since the insufficient cooking time observed was, sometimes, at the origin of low temperatures (37-89 degrees C). The influence of both the initial concentration of Salmonella in the product and the heat storage before consumption on the final risk was studied. For a high initial concentration of Salmonella in the product, when the 'cordons bleus' are fryer cooked, the average risk of salmonellosis was equal to 3.95 x 10(-3) without storage before consumption and 2.8 x 10(-4) if the product is consumed after storage. This paper presents the results of the QRA and discusses risk management options to minimize the risk of salmonellosis.

Phage types of Salmonella enteritidis isolated from clinical and food samples, and from broiler carcasses in southern Brazil

272 isolates of Salmonella Enteritidis (111 isolated from frozen broiler chicken carcasses, 126 from human food and other biological materials involved in food poisoning outbreaks and 35 from different poultry materials) were selected for phage typing. From these, 111 were phage typed, 57.65% being classified as phage type 4, 32.43% as phage type 4a, 3.60% as phage type 6a and 0.90% as phage type 7, whereas 5.40% samples were not phage typeable. The predominance of phage type 4 is in agreement with the results published worldwide, and reinforces the need for studies related to the epidemiological meaning of these findings.

Outbreak of Salmonella Potsdam associated with salad dressing at a restaurant

Between 27 January and 7 February 2002, 12 cases of Salmonella Potsdam infection were notified to NSW Health of which nine were residents of the Hunter Health Area. Interviews with two cases notified by two local doctors initiated the investigation and revealed exposure to foods from the same restaurant (restaurant A). All New South Wales S. Potsdam cases, those accompanying cases to restaurant A and people from restaurant A booking lists were interviewed. Of the 34 people interviewed, 17 met the case definition. The epidemiological investigation did not detect a food source of S. Potsdam infection, however, shell egg-based Caesar salad dressing and mayonnaise, and a swab of a cap from a mayonnaise bottle collected at restaurant A tested positive for S. Potsdam. Environmental and laying hen feed samples from the egg supplier to restaurant A and meat meal, (the major component of laying hen feed) tested positive for various Salmonella serotypes. The investigation identified problems of inadequate cleaning, time-temperature abuse, and ignorance of the hazardous nature of raw shell eggs at the restaurant level, poor sanitation and a lack of hygiene inspections at the egg production level, and problems with cleaning, storage and lack of bacterial monitoring of final product at the animal rendering plant. Investigation of 12 notified cases of Salmonella resulted in public health interventions, which likely prevented further cases of foodborne disease due to Salmonella and other pathogens in the Hunter Health Area and elsewhere in New South Wales.

Collaborative investigation of an outbreak of Salmonella enterica serotype Newport in England and Wales in 2001 associated with ready-to-eat salad vegetables

In June 2001, as part of a microbiological study of bagged, ready-to-eat salad products, Salmonella enterica serotype Newport was isolated from a sample of pre-packed green salad distributed by a major supermarket retailer. The strain was characterised by phage typing, plasmid profile typing and pulsed-field gel electrophoresis. Other isolates of S. Newport from cases of human infection in England and Wales in the first six months of 2001 were similarly characterised. Of 60 strains from cases of human infection, 19 were found to be indistinguishable from that isolated from the salad product. This study highlights the benefits of an integrated approach to outbreak investigations, involving the various elements of the PHLS and the Food Standards Agency, and acknowledges the full co-operation of the retailer in ensuring the rapid withdrawal of the contaminated product.