International epidemiological and microbiological study of outbreak of Salmonella agona infection from a ready to eat savoury snack--II: Israel.

OBJECTIVES: To explain an increase in the incidence of salmonellosis caused by Salmonella agona in Israel between October 1994 and January 1995 in the light of an outbreak of S agona phage type 15 infection in England and Wales caused by consumption of a ready to eat savoury snack produced in Israel. DESIGN: Epidemiology of S agona in 1994-5 was analysed and two consecutive, case-control studies of 32 and 26 case-control pairs were performed. Phage typing and molecular methods were used to characterise strains of S agona isolated from cases and samples of the snack in Israel and England and Wales. RESULTS: The increase in the incidence of S agona between October 1994 and January 1995 was countrywide. Cases of infection with group B salmonella increased from 60% to 80% in children under 5 years old. In both case-control studies, cases consumed more of the snack than did controls (4.25 v 2.94 packets per week in the first study (P = 0.086) and 4.04 v 2.37 packets per week in the second study (P = 0.034)). When the two studies were combined there was a significant dose-response relation for the number of packets consumed weekly. Compared with consumption of less than two packets, the odds ratio was 1.43 for between two and six packets and 3.37 for seven or more packets (chi 2 for trend = 5.27, P = 0.02) S agona phage type 15 was isolated from a packet of the snack sold in Israel, and the strain was identical with those isolated from packets and cases in Israel and England and Wales. CONCLUSIONS: This outbreak of S agona was caused by the contamination of a snack produced in Israel. Even under modern operating conditions, large, widespread international outbreaks of foodborne disease can occur. The success of this investigation resulted from excellent international collaboration between public health authorities.     

Large outbreak of Salmonella enterica serotype paratyphi B infection caused by a goats' milk cheese,France, 1993: a case finding and epidemiological study.

OBJECTIVE--To assess the magnitude of a nationwide outbreak of infection with Salmonella enterica serotype paratyphi B and identify the vehicle and source of infection. DESIGN--A case finding study of S paratyphi B infection between 15 August and 30 November 1993; a pair matched case-control study; an environmental investigation at a processing plant that produced a raw goats'' milk cheese incriminated in the outbreak; phage typing and genotyping of food and human S paratyphi B isolates. SETTING--France, 15 August to 30 November 1993. SUBJECTS--273 patients with S paratyphi B infection; 59 pairs of cases and controls matched for age, sex, and city of residence. MAIN OUTCOME MEASURES--Numbers of cases and incidence rates by region of residence and age; matched odds ratios for dairy food preferences. RESULTS--Among the 273 cases there was one death; 203 (78%) strains belonged to phage type 1 var 3. The incidence of infection was greatest in the region where goats'' milk cheese is commonly produced. Comparison of cases and controls showed a 12-fold greater risk of illness (95% confidence interval 1.6 to 92.3) from eating brand A unpasteurised goats'' milk cheese. S paratyphi B isolates of phage type 1 var 3 were recovered from cheese A, goats'' milk at the plant processing cheese A, and goats'' milk supplied to the plant by a single farm. Genotypic IS 200 typing of food and human 1 var 3 phage type isolates showed a common IS 200 pattern. CONCLUSION--This outbreak emphasises the potential health hazards of widely distributed unpasteurised milk products in France and the need for their close bacterial monitoring.     

Molecular analysis confirms food source and simultaneous involvement of two distinct but related subgroups of Salmonella typhimurium bacteriophage type 10 in major interprovincial Salmonella outbreak

More than 2,000 confirmed cases of food poisoning occurred in the four Atlantic provinces of Canada and in Ontario during the second and third quarters of 1984. Salmonella typhimurium phage type 10 was identified as the etiologic agent, and cheddar cheese was implicated as the source of infection. Strains isolated from infected humans and from cheese were indistinguishable by biotyping, antibiotic resistance typing, and phage typing. Plasmid analysis confirmed cheese as the source of infection and revealed the presence of two molecular subgroups of bacteriophage type 10. Group I strains carried 57-, 22.3-, and 3.4-kilobase (kb) plasmids; group II strains carried 57-, 4.6-, and 3.4-kb plasmids. Digestion with endonucleases HaeIII, HpaII, and AvaIII indicated that the 3.4-kb plasmids were identical. This outbreak was, therefore, caused by a mixed infection with two distinct but related bacteria. Group I strains are fairly common among Canadian S. typhimurium phage type 10 isolates, whereas group II strains appeared to be unique to this outbreak.     

Molecular analysis confirms food source and simultaneous involvement of two distinct but related subgroups of Salmonella typhimurium bacteriophage type 10 in major interprovincial Salmonella outbreak.

More than 2,000 confirmed cases of food poisoning occurred in the four Atlantic provinces of Canada and in Ontario during the second and third quarters of 1984. Salmonella typhimurium phage type 10 was identified as the etiologic agent, and cheddar cheese was implicated as the source of infection. Strains isolated from infected humans and from cheese were indistinguishable by biotyping, antibiotic resistance typing, and phage typing. Plasmid analysis confirmed cheese as the source of infection and revealed the presence of two molecular subgroups of bacteriophage type 10. Group I strains carried 57-, 22.3-, and 3.4-kilobase (kb) plasmids; group II strains carried 57-, 4.6-, and 3.4-kb plasmids. Digestion with endonucleases HaeIII, HpaII, and AvaIII indicated that the 3.4-kb plasmids were identical. This outbreak was, therefore, caused by a mixed infection with two distinct but related bacteria. Group I strains are fairly common among Canadian S. typhimurium phage type 10 isolates, whereas group II strains appeared to be unique to this outbreak.     

Bacteriophage types represented by lactose-fermenting Salmonella agona strains

Bacteriophage typing was performed on 1911 S. agona, lactose-fermenting strains. These strains were isolated from hospitalised newborns and neonates patients. Out of 1911 strains 98.8% were typable by means of phage set prepared for strains differentiation of Salmonella agona showing typical biochemical properties. It was shown that in 16 provinces from which the strains were obtained in 1983-1985 type V (49.5%) and type XI (25.4%) prevailed. Subtypes VA and VB were distinguished within type V. Altogether 20.3% of strains were classified as belonging to these subtypes. Their lytic reaction was weaker with phages 3, 4, and 9 with the characteristic range of phage type V strains. Among tested strains types I, XIII, and XVI were also represented composing 2, 6, 0, 9, and 0.3% of total number of strains respectively. 1.5% of strains were nontypable and 0.2% showed lytic reactions different from that included in up to now used scheme of typing. It can be concluded that lactose-fermenting S. agona strains show susceptibility to lowered number of phages than typical for Salmonella species strains. It seems that differentiation of this atypical biochemical variant of S. agona with, the use of phage set used up to now may be also usefull in practice as it is the case in respect to strains with typical biochemical properties.     

Public Health Investigation of Two Outbreaks of Shiga Toxin-Producing Escherichia coli O157 Associated with Consumption of Watercress

An increase in the number of cases of Shiga toxin-producing Escherichia coli (STEC) O157 phage type 2 (PT2) in England in September 2013 was epidemiologically linked to watercress consumption. Whole-genome sequencing (WGS) identified a phylogenetically related cluster of 22 cases (outbreak 1). The isolates comprising this cluster were not closely related to any other United Kingdom strain in the Public Health England WGS database, suggesting a possible imported source. A second outbreak of STEC O157 PT2 (outbreak 2) was identified epidemiologically following the detection of outbreak 1. Isolates associated with outbreak 2 were phylogenetically distinct from those in outbreak 1. Epidemiologically unrelated isolates on the same branch as the outbreak 2 cluster included those from human cases in England with domestically acquired infection and United Kingdom domestic cattle. Environmental sampling using PCR resulted in the isolation of STEC O157 PT2 from irrigation water at one implicated watercress farm, and WGS showed this isolate belonged to the same phylogenetic cluster as outbreak 2 isolates. Cattle were in close proximity to the watercress bed and were potentially the source of the second outbreak. Transfer of STEC from the field to the watercress bed may have occurred through wildlife entering the watercress farm or via runoff water. During this complex outbreak investigation, epidemiological studies, comprehensive testing of environmental samples, and the use of novel molecular methods proved invaluable in demonstrating that two simultaneous outbreaks of STEC O157 PT2 were both linked to the consumption of watercress but were associated with different sources of contamination.     

The highly virulent 2006 Norwegian EHEC O103:H25 outbreak strain is related to the 2011 German O104:H4 outbreak strain

In 2006, a severe foodborne EHEC outbreak occured in Norway. Seventeen cases were recorded and the HUS frequency was 60%. The causative strain, Esherichia coli O103:H25, is considered to be particularly virulent. Sequencing of the outbreak strain revealed resemblance to the 2011 German outbreak strain E. coli O104:H4, both in genome and Shiga toxin 2-encoding (Stx2) phage sequence. The nucleotide identity between the Stx2 phages from the Norwegian and German outbreak strains was 90%. During the 2006 outbreak, stx(2)-positive O103:H25 E. coli was isolated from two patients. All the other outbreak associated isolates, including all food isolates, were stx-negative, and carried a different phage replacing the Stx2 phage. This phage was of similar size to the Stx2 phage, but had a distinctive early phage region and no stx gene. The sequence of the early region of this phage was not retrieved from the bacterial host genome, and the origin of the phage is unknown. The contaminated food most likely contained a mixture of E. coli O103:H25 cells with either one of the phages.     

Inter-strain comparison by pyrolysis mass spectrometry of Staphylococcus aureus isolates associated with nosocomial infection

Pyrolysis mass spectrometry was used to characterise Staphylococcus aureus isolates from an outbreak of post-operative wound infections on a mixed surgical ward. The PyMS results were compared with those of phage typing. Both suggested a single strain of S. aureus, of phage type 3C, 55,71, was responsible for six of the 13 wound infections. PyMS differentiated an isolate from a member of staff of similar phage type to the epidemic strain, which had previously been considered to be the point source for the outbreak. PyMS is a rapid and inexpensive technique for investigating nosocomial outbreaks, including those caused by S. aureus and, in this instance, was more discriminatory than phage typing.     

Epidemic strains of Salmonella agona differentiated by phage restriction and u. v.-protection markers on Collb plasmids

Genes for phage restriction and u. v.-protection, carried by some Coll plasmids, are useful markers of plasmids carried by host bacteria. Colicinogeny, with associated marker characters, may prove useful for strain differentiation as it did, in this study, with strains of Salmonella agona involved in an outbreak.     

Paratyphoid in Man and Cattle

Salmonella paratyphi B, phage type Taunton, caused generalized subclinical infection of cows and cases of human enteric fever at a dairy farm. The cattle were probably infected from a stream receiving the sewage effluent of a village in which a chronic carrier lived. At the same time as the farm outbreak a water-borne outbreak of human paratyphoid fever occurred in villages several miles away. The water supply was chlorinated and no failure of its treatment had been detected. S. paratyphi B, type Taunton, was isolated from the septic tank of a cottage near the water source and from soil over a break in the effluent pipe. Several inhabitants of the cottage worked at the infected dairy farm and one showed serological evidence of infection.Attention is drawn to the lack of statutory powers which could be applied to prevent the spread of the disease from the dairy herd and to the hazards of simple chlorination in the absence of additional safeguards of a water supply liable to pollution by surface water.     

Illness outbreak associated with Escherichia coli O157:H7 in Genoa salami

BACKGROUND: An outbreak of Escherichia coli O157:H7 infection was identified in the spring of 1998, with a 7-fold increase in the number of laboratory-confirmed E. coli O157:H7 cases in southern Ontario. This prompted an intensive investigation by local, provincial and federal public health officials. METHODS: Case interviews of 25 people from southern Ontario were conducted using a broad food history and environmental exposure survey. Laboratory investigations involved both case and food sampling. Specimens of foods sold locally and reportedly consumed by those affected were tested. Common suppliers of suspected foods were identified by cross-referencing suppliers'' lists with stores frequented by those who fell ill. A case-control study involving 25 cases and 49 age-matched controls was conducted. This was followed by a comprehensive environmental investigation of the meat processing plant identified as the source of the E. coli. RESULTS: Thirty-nine outbreak-related cases occurred between April 3 and June 2, 1998. Of the 36 case specimens tested all were positive for E. coli O157:H7. The case-control study identified Genoa salami as the most probable (odds ratio 8 [confidence interval 2-35]) source of the outbreak. Samples of Genoa salami produced by the most commonly identified supplier later tested positive for E. coli O157:H7, and the pathogen matched the same pulsed-field gel electrophoresis pattern and phage type of the case specimens. INTERPRETATION: Our investigation, which led to a national recall of the brand of dry fermented Genoa salami identified as the source of the outbreak, supports an adherence to stringent manufacturing requirements for fermented meat products. A review of the Canadian standards for fermented meat processing and the effectiveness of their implementation is warranted.     

Analysis of epidemic and sporadic strains of Listeria monocytogenes by pyrolysis mass spectrometry

Twenty-six cultures of Listeria monocytogenes , serovar 4b, including 10 from a food-borne outbreak in Switzerland and sporadic patient and food isolates from both Switzerland and the UK, were compared by pyrolysis mass spectrometry (PMS). This clustered all of the Swiss epidemic isolates with four other isolates indistinguishable from the Swiss strain by phage typing, a phage non-typable isolate from a Swiss patient not known to be part of the epidemic and two strains (both from Switzerland) of a different phage type. The eight strains excluded from the PMS-derived cluster were all either known to be unrelated to the epidemic, or of a phage type distinct from the epidemic strain, or both.     

Multiple-locus variable-number tandem repeat analysis of Salmonella enterica subsp. enterica serovar Typhimurium: comparison of isolates from pigs, poultry and cases of human gastroenteritis

AIMS: Pulsed-field gel electrophoresis (PFGE) and variable number tandem repeat (VNTR) profiles of 195 epidemiologically unrelated Salmonella Typhimurium strains isolated in 1997-2004 from pigs were analysed and the results compared to establish the discriminatory ability of each method. In order to investigate the epidemiology of S. Typhimurium from different populations, the VNTR profiles from pigs were compared with those obtained from 190 S. Typhimurium strains isolated from poultry and 186 strains isolated from human cases of gastroenteritis. METHODS AND RESULTS: A total of 195 strains of S. Typhimurium were tested by PFGE and VNTR. For PFGE, the restriction enzyme XbaI was used, and for VNTR, the number of repeats at five loci (STTR 9, 5, 6, 10pl and 3) were counted and assigned an allele number based on an established VNTR scheme. The results obtained showed improved discrimination of VNTR when compared with PFGE with 34 PFGE profiles identified compared with 96 different VNTR profiles for the pig isolates and 56 different VNTR types within the most common PFGE type. Within the three different populations, VNTR showed distinct subpopulations of VNTR type related not only to source, but also demonstrated common VNTR types within samples obtained from humans, poultry and pigs, especially in strains of phage type DT104. CONCLUSIONS: VNTR has taken the discrimination to a further level than that obtained through PFGE, and demonstrated an overlap in the genetic diversity of isolates tested across the three different populations, confirming previous suggestions that animals have an involvement in the dissemination of S. Typhimurium through the food chain. SIGNIFICANCE AND IMPACT OF THE STUDY: Salmonella Typhimurium remains an important concern as a food-borne zoonotic agent. The VNTR strategy described provides an accurate method of tracing strain dissemination, and adds a further level of discrimination to the PFGE type, providing potential benefits to epidemiological studies and the possibility of deciphering source attribution of cases.     

Antimicrobial biotypes and colicine types: potential epidemiological markers of Salmonella agona

With the purpose of characterizing epidemiologic markers, 240 strains of S. agona isolated from differents sources (man, food and environment) and obtained from five Brazilian States (Minas Gerais, S?o Paulo, Rio de Janeiro, Pernambuco and Rio Grande do Sul) were analysed. The susceptibility to 15 antimicrobial agents and numeric codification of the resistance profiles allowed us to recognize 56 antibiotic resistance biotypes, while 40 strains were able to produce colicine, belonging to the types: Ia (55%); B (32.5%); Ib (10%) and untypable (2.5%). The application of these elements into intra-serotype differentiation is discussed.     

Foodborne gastroenteritis due to Norwalk virus in a Winnipeg hotel.

Within 1 week four separate incidents of gastroenteritis presumed to be foodborne were reported by guests of a Winnipeg hotel. Investigation revealed poor food-handling practices and illness among the kitchen staff. Elevated bacterial counts and Escherichia coli were found in 15 of 24 samples of food tested, and Staphylococcus aureus was isolated from 2 pastry samples. Culture of 14 stool samples for bacteria yielded Clostridium perfringens in 1 sample from a staff member and coagulase-positive S. aureus in 2 samples from staff members and 3 from guests. All of the S. aureus isolates were nonenterotoxigenic and had three different phage patterns. Electron microscopy and immunoelectron microscopy revealed the prototype Norwalk virus in five (56%) of nine stool samples; four samples were from guests, and one was from a kitchen employee. The employee had had diarrhea 24 hours before the first outbreak and was thus believed to be the source of the virus infection, possibly through food handling. This is the first report of Norwalk virus isolation and the first of foodborne Norwalk virus transmission in Canada. A review of foodborne Norwalk virus infections is presented.     

Application of pulsed-field gel electrophoresis to laboratory surveillance of small community outbreaks of Salmonella enterica serovar Typhimurium

Infectious diarrhea syndrome is an important cause of human morbidity around the world, and Salmonella genus remains one of the most prevalent etiology. Salmonella enterica serovar Typhimurium outbreak-associated isolates received by the Laboratory for Enteric Pathogens from N.I.R.D.M.I. "Cantacuzino" for confirmation and typing were analyzed by genomic pulsed-field gel electrophoresis (PFGE) and phage susceptibility testing to establish their relatedness. Both typing methods proved to have similar discriminatory power. The isolates originating from the same outbreak belonged to the same phage type and showed indistinguishable PFGE profiles. The molecular characterization of autochthonal Salmonella enterica Typhimurium outbreak human isolates provided laboratory evidence that epidemiologically related isolates collected from community outbreaks of disease were also genetically related. In order to improve the national and international surveillance of major foodborne pathogens the reference laboratory centers are required to establish and maintain the capacity to perform a wide range of both phenotypic and genotypic methods to support outbreak investigations.     

Clonal relations among Salmonella enteritidis phage type 3 outbreak isolates traced by DNA fingerprinting.

Isolates of Salmonella enteritidis PT3, a rare phage type, were recovered from patients and strains were isolated from an outbreak of gastroenteritis that occurred during the summer of 1997 in North-East Sardinia, Italy. To investigate possible clonal involvement in the outbreak and to evaluate the capacity to discriminate among S. enteritidis PT3 strains, a number of molecular typing methods including ribotyping with a mixture of PstI and SphI (PS-ribotyping), PFGE with endonuclease XbaI and RAPD typing with four arbitrary primers was used. The typical XbaI endonuclease generated PFGE pattern also explained the prevalence of highly clonal S. enteritidis PT3 strains in the outbreak and adjacent areas. RAPD fingerprinting with primers OPA 4, OPB 15, OPB17 and P1254 exhibited a single but unique RAPD profile among the outbreak strains from various sources that differed significantly from control strains. The results of this study showed that when an appropriately chosen set of primers is employed, RAPD fingerprinting can be used as an alternative, rapid, highly reproducible technique for tracing the clonal relations of S. enteritidis PT3, and can be more discriminatory than PFGE. Furthermore, this study revealed the possibility of PT3 causing outbreak.     

Estimating size and diversity of nitrifying communities in deodorizing filters using PCR and immunofluorescence

Thirty isolates of Listeria monocytogenes and 18 of L. innocua obtained from different short-ripened cheeses manufactured in Asturias (northern Spain), were compared with each other and with reference strains using serotype, phage type and pulsed-field restriction endonuclease digestion profiles analysis of the total DNA. Restriction enzymes Apa I and Sma I defined five clusters in L. monocytogenes ( m1 to m5 ) and two main clusters in L. innocua ( i1 and i2 ). Cluster i2 was further arranged into three subclusters ( i2a , i2b and i2c ) based on the different Eco 52I ( Xma III) and Crf 42I ( Sac II) patterns of its isolates. Clusters of L. innocua were clearly different whereas those of L. monocytogenes were more closely related to each other. In this latter species, serotype 4b isolates ( m4 and m5 ) constituted a more homogeneous group than serogroup 1 isolates ( m1 , m2 and m3 ). Cluster m3 contained two strains of serotype 1/2a whereas m1 and m2 harboured strains of both serotypes, 1/2a and 1/2b. Therefore, the combined use of restriction patterns and serotype may be useful to differentiate L. monocytogenes strains showing identical restriction profiles but differing in serotype. The cheese source of Listeria strains proved that isolates from cluster m1 were repeatedly detected as a contaminant in the same type of cheese. Comparison of L. monocytogenes Apa I profiles showed a genetic proximity of m4 and m5 to the recognized pathogenic strains ATCC 13932 and NCTC 11994, responsible for meningitis cases in other countries. Finally, bacteriophage typing data indicated that m4 , the sole phage typable group, had a phage type resembling that of strains causing the Auckland (New Zealand) outbreak of listeriosis in 1969. These data suggest a wide distribution of closely related types which might cause, under several circumstances, sporadic cases of listeriosis.     

Analysis of clinical and food-borne isolates of Listeria monocytogenes in the United States by multilocus enzyme electrophoresis and application of the method to epidemiologic investigations

To investigate the microbiology and epidemiology of the 1,700 sporadic cases of listeriosis that occur annually in the United States, we developed a multilocus enzyme electrophoresis (MEE) typing system for Listeria monocytogenes. We studied 390 isolates by MEE. Eighty-two electrophoretic types (ETs) were defined. Two distinct clusters of ETs, ET group A (ETGA) and ET group B (ETGB), separated at a genetic distance of 0.440, were identified. Strains of ETGB were associated with perinatal listeriosis (P = 0.03). All strains of H antigen type a were in ETGA, while all strains of H antigen type b were in ETGB. Among 328 clinical isolates from cases of literiosis, 55 ETs of L. monocytogenes were defined. Thirty-four ETs were identified among 62 isolates from food products. The mean number of strains per ET (5.2) was significantly higher among clinical isolates than among food-borne isolates. Examination of isolates from outbreaks further documented the link between cases and contaminated food products. In one investigation, we found 11 different ETs, ruling out a single common source as a cause of that outbreak. By examining a large number of isolates collected over a specified time in diverse geographic locations in the United States, we have begun to establish a baseline for the study of the epidemiology of listeriosis by MEE.