In developing public policy on food safety, systematic identification and thorough investigation of all general outbreaks is necessary in order to avoid bias towards highly publicised outbreaks. In Wales, from 1986 to 1998, 87 general foodborne outbreaks of salmonellosis were identified. Most outbreaks occurred at functions or were associated with small catering outlets such as bakeries and sandwich bars. In 50 outbreaks, a vehicle of infection was confirmed microbiologically and/or epidemiologically. The most common food vehicles were those containing shell eggs. Salmonella enteritidis outbreaks were significantly more likely than outbreaks of other serotypes to be associated with vehicles containing shell eggs, suggesting that eggs were also the source of infection in many outbreaks. The routine use of analytical epidemiological studies to identify vehicles in outbreaks is recommended.

In 1995, Salmonella Enteritidis (SE) cases in the state of Utah increased fivefold. Isolates were identified as phage type 4 (PT4). Risk factors and sources of infection were investigated in two case-control studies, a traceback of implicated foods, and environmental testing. Forty-three patients with sporadic infections and 86 controls were included in a case-control study of risk factors for infection. A follow-up case-control study of 25 case and 19 control restaurants patronized by case and control patients examined risks associated with restaurant practices. In the first case-control study, restaurant dining was associated with illness (P = 0·002). In the follow-up case-control study, case restaurants were likelier to use > 2000 eggs per week (P < 0·02), to pool eggs (P < 0·05), and to use eggs from cooperative ‘A’ (P < 0·009). Eggs implicated in separately investigated SE PT4 outbreaks were traced to cooperative ‘A’, and SE PT4 was cultured from one of the cooperative's five local farms. We conclude that SE PT4 transmitted by infected eggs from a single farm caused a fivefold increase in human infections in Utah.

Salmonella constitutes a genus of zoonotic bacteria of worldwide economic and health importance. The current view of salmonella taxonomy assigns the members of this genus to two species: S. enterica and S. bongori. S. enterica itself is divided into six subspecies, enterica, salamae, arizonae, diarizonae, indica, and houtenae, also known as subspecies I, II, IIIa, IIIb, IV, and VI, respectively [1]. Members of Salmonella enterica subspecies enterica are mainly associated with warm-blooded vertebrates and are usually transmitted by ingestion of food or water contaminated by infected faeces. The pathogenicity of most of the distinct serotypes remains undefined, and even within the most common serotypes, many questions remain to be answered regarding the interactions between the organism and the infected host.

Salmonellosis manifests itself in three major forms: enteritis, septicaemia, and abortion, each of which may be present singly or in combination, depending on both the serotype and the host involved. Although currently over 2300 serovars of Salmonella are recognized, only about 50 serotypes are isolated in any significant numbers as human or animal pathogens [2, 3] and they all belong to subspecies enterica. Of these, most cause acute gastroenteritis characterized by a short incubation period and a severe systemic disease in man or animals, characterized by septicaemia, fever and/or abortion, and such serotypes are often associated with one or few host species [4–6].

It is the intention of this review to present a summary of current knowledge of these host-adapted serotypes of S. enterica. The taxonomic relationships between the serotypes will be discussed together with a comparison of the pathology and pathogenesis of the disease that they cause in their natural host(s). Since much of our knowledge on salmonellosis is based on the results of work on Typhimurium, this serotype will often be used as the baseline in discussion. It is hoped that an appreciation of the differences that exist in the way these serotypes interact with the host will lead to a greater understanding of the complex host–parasite relationship that characterizes salmonella infections.

In June 1998, an increased number of persons with Salmonella blockley infection were reported from one German state. Because S. blockley is extremely uncommon in Germany, a case-control study was performed in order to find the source. A total of 13 patients met the case definition. Nine of 12 cases and 2 of 21 controls with food consumption histories reported eating smoked eel (OR 28·5; 95% CI 3·9–235·3). The consumed eel came from four different local smokeries, but could be traced back to fish farms in Italy. This outbreak indicates that eel may be a vehicle for salmonella infection and that the smoking process may not eliminate bacterial contamination from raw fish.

The number of human visitors to Antarctica is increasing rapidly, and with it a risk of introducing infectious organisms to native animals. To study the occurrence of salmonella serotypes in sub-Antarctic wildlife, faecal samples were collected from gentoo penguins, macaroni penguins, gray-headed albatrosses, black-browed albatrosses and Antarctic fur seals on Bird Island in the South Georgian archipelago during the austral summer of 1996 and 1998. In 1996, S. havana, S. typhimurium and S. enteritidis were isolated from 7% of gentoo penguins and 4% of fur seals. In 1998, however, 22% of fur seals were found to be infected with S. havana, S. enteritidis and S. newport. All isolates, except one, showed identical pulsed-field gel electrophoresis-patterns within each serotype, irrespective of sampling year and animal reservoir. No significant antibiotic resistance was found. The very low heterogeneity in the salmonella isolates found could either indicate a high genetic adaptation of the bacteria to the environment or a recent introduction of salmonella into the area.

The antimicrobial resistance of 809 Salmonella Typhimurium isolates collected from humans in Norway between 1975 and 1998 was studied. The material was subdivided into domestic and foreign isolates according to whether the patient had recently travelled abroad or not. In imported isolates the largest increase in resistance was in 1996 when 35% of the isolates were multi-resistant. The first multi-resistant isolate acquired in Norway appeared in 1994, but already in 1998 23% of the isolates domestically acquired were multi-resistant, and a majority were S. Typhimurium DT104. We found no ciprofloxacin resistance in domestically acquired isolates. Amplified fragment length polymorphism analysis was performed on selected multi-resistant isolates. The method discriminated well between different multi-resistant isolates, but not between DT104 isolates. Resistant and multi-resistant S. Typhimurium were until 1998 essentially recovered from patients who had travelled abroad, but multi-resistant isolates, mainly DT104, are now also being transmitted within the country.

Different genetic typing procedures were applied in an epidemiological study of Salmonella serotype Ohio. Isolates that generated identical DNA fingerprints (HincII ribotypes, ERIC and RAPD profiles) were clustered into the same lineage, and the addition of data from plasmid, integron and resistance profiles was used to differentiate types. Results led to the determination of the endemic and the emergent epidemic types at specific times, and to ascertain the clinical and epidemiological impact of each type. In the series analysed (47 clinical isolates and 3 non-clinical isolates) 11 lineages and 32 types were found. Two lineages were considered prevalent and endemic, and during an epidemiological alert (Spain, 1998) a re-emergence and spread of organisms mainly from the most frequent lineage had occurred. The combination of H-ribotype with ERIC profile, as primary markers, and resistance profile with plasmid profile, as secondary markers, was shown to be the most useful tool to trace epidemiologically Ohio.

A Mix-ELISA using lipopolysaccharide antigens from Salmonella enterica serotype Enteritidis and Typhimurium was evaluated using samples collected over time in the Danish salmonella surveillance programme for poultry. Serological samples (n = 42813) taken from broiler-breeder flocks after a year of bacteriological monitoring with negative results were used for calculating the flock and individual test specificities, which were 0·997 and 0·999, respectively. Layer flocks from the table egg sector were used for calculation of positive predictive values. In the survey, flocks were examined for salmonella by Mix-ELISA and by faecal culture, and in case of a positive result in either of these a repeated, serological testing was performed, and 60 animals were organ-cultured. If one of these samplings was positive, the flock was declared salmonella infected. In a period of 3 months, 35 flocks were found to be positive in the routine samples. Of these, 32 were serologically positive, 2 both serologically and faecally positive and 1 flock only faecally positive. For flocks serologically positive in the surveillance programme, a positive-predictive value of 0·62 for organ culture positivity was found, and while considering serological follow-up samples, the value was 0·95.

We report the first documented Campylobacter jejuni outbreak in an Austrian youth centre. Sixty-four children were involved of which 38 showed classical signs of campylobacter gastroenteritis. Since unpasteurized milk distributed by a local dairy was suspected to be the source of infection, stool samples were collected from 20 cows providing the milk. Five of the cows tested positive for C. jejuni. These isolates together with 37 clinical samples were compared by pulsed-field-gel electrophoresis (PFGE). The PFGE patterns, using the restriction endonucleases SmaI and SalI, were identical for the human and bovine isolates.This finding confirmed that the outbreak was caused by the consumption of unpasteurized milk contaminated with C. jejuni.

Active surveillance of Vibrio parahaemolyticus infection among hospitalized patients in Calcutta, India, showed the appearance of the O4[ratio ]K68 serovar for the first time in March 1998 alongside the continued predominant incidence of the O3[ratio ]K6 serovar. Strains belonging to both these serovars have been reported to possess pandemic potential. The genomes of O3[ratio ]K6 and O4[ratio ]K68 strains and for comparison, non-O3[ratio ]K6 and non-O4[ratio ]K68 strains isolated from two different countries, India and Thailand, were examined by different molecular techniques to determine their relatedness. The O3[ratio ]K6 and O4[ratio ]K68 strains from Calcutta and Bangkok carried the tdh gene but not the trh gene. Characterization of representative strains of these two serovars by ribotyping and by arbitrarily primed-polymerase chain reaction (AP-PCR) showed that the isolates had identical ribotype and DNA fingerprint. Pulsed-field gel electrophoresis (PFGE) performed with the same set of strains yielded nearly similar restriction fragment length polymorphism (RFLP) patterns for the O3[ratio ]K6 and O4[ratio ]K68 isolates from Calcutta and Thailand. Phylogenetic analysis of the NotI RFLP showed that the O3[ratio ]K6 and O4[ratio ]K68 strains formed a cluster with 78–91% similarity thus indicating close genetic relationship between the two different serovars isolated during the same time-frame but from widely separated geographical regions. The non-O3[ratio ]K6 and non-O4[ratio ]K68, in contrast, showed different ribotype, AP-PCR and PFGE patterns.

An outbreak of salmonellosis occurred among 63 wedding participants. The outbreak was investigated through cohort, laboratory, and environmental studies. Consumption of rice-dressing made from a commercially cooked, meat-based, rice-dressing mix was strongly associated with illness. Nineteen patient isolates, six company/grocery store isolates cultured from the rice-dressing mix, and one environmental isolate from a pump in the production line were of an identical outbreak strain of Salmonella Infantis characterized by pulsed-field gel electrophoresis. In the production line, cooked rice-dressing mix tested negative for S. Infantis before and positive after contact with the contaminated pump. The dressing-mix had an estimated 200 colony-forming units of salmonella per gram of product, and > 180 000 pounds were distributed in 9 states for [ges ] 2 months before contamination was recognized. Food manufacturers should be required to use systematic, hazard analysis critical control point risk management practices for all processed meat products, validated by periodic microbiologic monitoring of the end product.

A case-control study was conducted in western Sweden (Älvsborg County). The aim of the study was to identify any special food items or behaviours associated with an increased risk of contracting campylobacter infection. A total of 101 cases and 198 controls were matched for age, sex and district of residence. The following risk factors or risk behaviours were associated with campylobacter infection: drinking unpasteurized milk (OR 3·56, 95% CI 1·46–8·94), eating chicken (OR 2·29, 95% CI 1·29–4·23), or eating pork with bones (chops OR 2·02, 95% CI 1·17–3·64; loin of pork OR 1·83, 95% CI 1·07–3·12), barbecuing (OR 1·98, 95% CI 1·10–4·34), and living or working on a farm (farm OR 3·06, 95% CI 1·58–6·62, hen/chicken-breeder OR 3·32, 95% CI 1·56–6·78), daily contact with chickens or hens (OR 11·83, 95% CI 3·41–62·03).

An outbreak of gastro-enteritis occurred in a community of 2213 persons located near the city of Ioannina, in North-western Greece. Two hundreds and eighty-eight inhabitants of the village of Eleoussa, suffered from gastro-enteritis between 11 and 22 October. The peak of the epidemic occurred during the first 3 days (11–13 October). The highest risk of developing gastro-enteritis was observed in the age group 0–14 years (41·4%) and decreased significantly with age (P < 0·01). Patients over 65 years were more frequently hospitalized than those in other age groups (P < 0·05). Shigella sonnei was isolated from both, water samples and faeces of patients. Control measures were implemented on the second day of the outbreak. Environmental conditions suggest that contamination of the water system occurred by groundwater.

Eighty-four strains of Vibrio cholerae O1, O139 and non-O1/non-O139 from clinical and environmental sources were investigated for the presence of the toxin co-regulated pilus gene, tcpA, the virulence cassette genes ctxA, zot, ace and cep and also for their ability to elaborate haemolysin and protease. The ctxA and zot genes were detected using DNA–DNA hybridization while the ace, cep and tcpA genes were detected using PCR. Production of haemolysin and protease was detected using mammalian erythrocytes and an agar diffusion assay respectively. Analysis of their virulence profiles showed six different groups designated Type I to Type VI and the major distinguishing factor among these profiles was in the in vitro production of haemolysin and/or protease. Clinical O1, O139 and environmental O1 strains were similar with regard to presence of the virulence cassette genes. All environmental O1 strains with the exception of one were found to possess ctxA, zot and ace giving rise to the probability that these strains may actually be of clinical origin. One strain which had only cep but none of the toxin genes may be a true environmental isolate. The virulence cassette and colonization factor genes were absent in all non-O1/non-O139 environmental strains but production of both the haemolysin and protease was present, indicating that these may be putative virulence factors. These findings suggest that with regard to its pathogenic potential, only strains of the O1 and O139 serogroup that possess the tcpA gene which encodes the phage receptor, have the potential to acquire the CTX genetic element and become choleragenic.

In the UK the increasing use of pre-admission parenteral antibiotic therapy in meningococcal disease has lessened the value of routine cultures as a tool to confirm diagnosis, and laboratory confirmation of invasive meningococcal infection is achieved increasingly by non-culture, nucleic acid amplification methods. The purpose of this study was to evaluate a DNA extraction and meningococcal-specific DNA amplification methodology for detection of meningococci from oropharyngeal swabs.

One hundred and six swabs from suspected or confirmed cases of meningococcal disease, and 94 swabs from contacts of meningococcal disease cases were examined. Of laboratory-confirmed cases, 38/65 (58·5%) yielded a positive oropharyngeal swab PCR result and 5/24 (20·8%) swabs from suspected but laboratory-unconfirmed cases were PCR positive. No significant differences in PCR positivity rates were found between the types of swab transport systems utilized, but transport time to the testing laboratory was found to affect PCR positivity (P < 0·05).

Application of meningococcus-specific PCR to oropharyngeal swabs, in addition to routine culture of swabs, can provide valuable epidemiological information as well as case confirmation for contact management. PCR amplification of meningococcal PCR from oropharyngeal swabs will also increase the ascertainment in swabbing surveys carried out as part of meningococcal disease outbreak investigation and management.

A new variant within the electrophoretic type (ET)-37 complex of Neisseria meningitidis, ET-15, first detected in Canada in 1986, has been associated with severe clinical infections and high mortality rates in several European countries, Israel and Australia. To ascertain the genetic and epidemiological relationships of ET-15 strains from different geographical areas, 72 ET-15 isolates from 10 countries were compared to 13 isolates representing other clones of the ET-37 complex. The 85 strains were analysed by pulsed-field gel electrophoresis (PFGE) using 2 restriction endonucleases and Southern hybridization with 10 genetic markers. Four ET-15 strains and 4 other strains of the ET-37 complex were further examined using an additional restriction enzyme and a total of 18 genetic markers. PFGE fingerprints of the ET-15 strains were closely related. Strains within each country were even more closely related, suggesting single introductions of the clone. Physical mapping of genes in ET-15 and other strains of the ET-37 complex demonstrated that large genetic rearrangements of the genome have occurred in association with the appearance of the ET-15 variant.

Two models estimating the proportion of Escherichia coli O157[ratio ]H7 cases not reported in the Ontario notifiable diseases surveillance system are described. The first model is a linear series of adjustments in which the total number of reported cases is corrected by successive under-reporting coefficients. The structure of the second model is based on a relative difference in the proportion of E. coli O157[ratio ]H7 cases which are hospitalized between the surveillance database and the underlying population.

Based on this analysis, the rate of under-reporting of symptomatic cases of E. coli O157[ratio ]H7 infection in Ontario ranges from 78 to 88% corresponding to a ratio of 1 reported case for approximately 4–8 symptomatic cases missed by the surveillance system. This study highlights the need to increase awareness among public health workers of the potential biases that may exist in the interpretation of routine surveillance data.

Infection with thermophilic Campylobacter spp. usually leads to an episode of acute gastroenteritis. Occasionally, more severe diseases may be induced, notably Guillain–Barré syndrome and reactive arthritis. For some, the disease may be fatal. We have integrated available data in one public health measure, the Disability Adjusted Life Year (DALY). DALYs are the sum of Years of Life Lost by premature mortality and Years Lived with Disability, weighted with a factor between 0 and 1 for the severity of illness. The mean health burden of campylobacter-associated illness in the Dutch population in the period 1990–5 is estimated as 1400 (90% CI 900–2000) DALY per year. The main determinants of health burden are acute gastroenteritis (440 DALY), gastroenteritis related mortality (310 DALY) and residual symptoms of Guillain–Barré syndrome (340 DALY). Sensitivity analysis demonstrated that alternative model assumptions produced results in the above-mentioned range.

Twenty-six isolates of the newly designated M90 serotype group A Streptococcus (GAS) from a large food-borne outbreak of pharyngitis in Greece and six M90 sporadic isolates from UK, were typed by pulsed-field gel electrophoresis (PFGE). Twenty-four outbreak isolates were identical and two closely related. The Greek isolates were possibly related with one UK isolate, while other sporadic isolates exhibited distinct PFGE profiles from the former isolates.

Plesiomonas shigelloides is often regarded as a non-pathogenic bacterial species that is occasionally isolated from patients with diarrhoea. However, a review of travellers returning to Japan with diarrhoeal illness through Kansai Airport revealed that the incidence of P. shigelloides from microbiologically confirmed cases increased from 23·2% in 1987 to 77·8% in 1999. We carried out a descriptive epidemiological study to identify patterns associated with diarrhoea due to this organism. Selected P. shigelloides isolates from this patient group were compared by pulsed-field gel electrophoresis of SpeI total chromosomal DNA digests to determine their genetic heterogeneity. Over the study period (whole of 1996 and first 2 months of 1999), 1149 of 1659 (69·3%) patients with microbiologically confirmed gastroenteritis yielded P. shigelloides. Infection was characterized by watery diarrhoea five times per day that persisted for 3 days. No statistically significant association was found between factors such as age, gender, destination, length of trip, but multivariable logistic regression analysis revealed an association between additional symptoms (vomiting, fever, abdominal pain) age and gender. The molecular fingerprints of a selection of 39 isolates and 3 reference strains of P. shigelloides were highly variable and each had a unique profile. We conclude that although P. shigelloides infections are usually mild and self-limiting, this organism may contribute to a significant proportion of travellers' diarrhoea in the Orient. The species is characterized by great heterogeneity at the DNA level.