International epidemiological and microbiological study of outbreak of Salmonella agona infection from a ready to eat savoury snack--I: England and Wales and the United States.

OBJECTIVES: To identify the source of an international outbreak of food poisoning due to Salmonella agona phage type 15 and to measure how long the underlying cause persisted. DESIGN: Case-control study of 16 primary household cases and 32 controls of similar age and dietary habit. Packets of the implicated foodstuff manufactured on a range of days were examined for salmonella. All isolates of the epidemic phage type were further characterised by pulsed field gel electrophoresis. RESULTS: 27 cases were identified, of which 26 were in children. The case-control study showed a strong association between infection with S agona phage type 15 and consumption of a peanut flavoured ready to eat kosher savoury snack imported from Israel. S agona phage type 15 was isolated from samples of this snack. The combined food sampling results from the United Kingdom, Canada, the United States, and Israel showed that contaminated snacks were manufactured on at least seven separate dates during a four month period between October 1994 and February 1995. Voluntary recalls of the product successfully interrupted transmission. CONCLUSIONS: Rapid international exchanges of information led to the identification of the source of a major outbreak of S agona in Israel and of associated cases in North America. The outbreak showed the value of the Salm-Net surveillance system and its links outside Europe, both for increasing case ascertainment and for improving the information on the duration of the fault at the manufacturing plant.     

Phage types of Australian isolates of Salmonella enterica subsp. enterica serovar Virchow

Australian isolates (79) of Salmonella enterica subsp. enterica serovar Virchow ( Salmonella Virchow) were characterized by phage typing. Thirteen phage types were identified, of which phage type (PT) 8, representing 54 of 79 isolates, was predominant, as it had been in England and Wales up to 1994 when it was replaced by PT26. Other phage types identified in Australia were distinct from those observed in England and Wales. This suggests that PT8 may be a global phage type, while others may be distinct to particular geographical regions.     

Conventional and molecular approaches to isolates of Salmonella hadar from sporadic and epidemic cases

In September 1994 an outbreak of gastroenteritis occurred in 437 people who had consumed lunch in the canteen of a factory in Central Italy. Salmonella sp. was isolated from stools of 99 patients and in 73 of them Salmonella hadar was identified. This is the first outbreak caused by this serotype described in Italy. In order to examine the genotypic basis of the epidemic strains, molecular typing was applied to sporadic strains isolated before and after the outbreak episode. For this purpose phage type, resistance to antibiotics, DNA plasmid profile and sites of insertion of the mobile element of IS200 were determined. The epidemic strains were genetically distinct from the non-epidemic isolates; they were shown to be phage type 26, harbouring four small plasmids, were resistant to nalidixic acid and showed a unique characteristic IS200 fingerprint. The typing methods used in this study allowed the identification and discrimination of the outbreak strains from related isolates. They can thus be considered as a tool for epidemiological purposes. In addition we should point out the emerging resistance to nalidixic acid, largely used in veterinary medicine, in Salm . hadar .     

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.     

Prevalence of antibiotic resistance and serotypes in pneumococci in England and Wales: results of observational surveys in 1990 and 1995.

OBJECTIVE--To assess the prevalence of antibiotic resistance and serotype distribution among pneumococci in England and Wales in 1990 and 1995. DESIGN--Observational surveys in March 1990 and March 1995. During two weeks in each survey period all pneumococci isolated in public health laboratories in England and Wales were collected and assessed for sensitivity to antibiotics and the distribution of serogroups or serotypes. SETTING--The network of public health laboratories throughout England and Wales. SUBJECTS--1127 individual patient isolates of Streptococcus pneumoniae obtained during the two surveys. MAIN OUTCOME MEASURES--Sensitivity or resistance to a range of antibiotics; serogroup or serotype. RESULTS--The prevalence of intermediate or full resistance to penicillin increased from 1.5% in 1990 to 3.9% in 1995 and resistance to erythromycin increased from 2.8% to 8.6%. About 92% of isolates belonged to serogroups or serotypes included in the currently available pneumococcal vaccine. CONCLUSION--Resistance to penicillin and erythromycin has increased among pneumococci in England and Wales. Continued surveillance to assess further increases in the prevalence of pneumococcal resistance to antibiotics is essential.     

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.     

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.     

Studies on halophilic vibrios causing a food poisoning outbreak in the city of Vladivostok

V. parahaemolyticus and V. alginolyticus strains isolated from patients during an outbreak of an acute enteric disease in Vladivostok in 1997 were studied. All strains were found to possess typical taxonomic signs. V. parahaemolyticus isolated from humans had direct heat stable haemolysin exotoxin. The overwhelming majority of these strains belonged to serovar O3K6. Among the cultures under study 7 phage types were determined: phage types 1, 2, 7, 10 in 8 V. parahaemolyticus strains and phage types 2, 4. 5. 7 in 5 V. alginolyticus strains. The diagnostic halophilic phage lyzed vibrios in 30.2% of strains. The cultures under study were found to be highly sensitive to chloramphenicol, cefotaxime, nalidixic acid and cyprofloxacin. The study proved that the outbreak of alimentary toxicoinfection was caused by vibrios of serogroup O3:K6.     

Selected properties of lactose-fermenting and non-fermenting Salmonella agona strains isolated from specimens from hospitalized infants

The aim of this study was to compare some of the properties of 28 lactose-positive and 28 lactose-negative Salmonella agona strains isolated from faeces of infants hospitalized in the same hospital. Some of biochemical properties, sensitivity to 14 antibiotics and chemotherapeutic agents and sensitivity to bacteriophages used for typing of this Salmonella genus were tested. Results of biochemical examinations revealed that lactose-fermenting strains retain the remaining of Salmonella of subspecies I. Two biochemical features are of particular importance: the ability to ferment lactose on all lactose containing media and a lack of the ability to produce H2S on Kligler medium. These two features differentiate lactose-fermenting strains of Salmonella from non-lactose fermenting ones. Antibiotic sensitivity pattern differed between lactose-positive and lactose-negative strains. Lactose-positive strains showed higher degree of resistance than lactose-negative strains. The differences in resistance were seen in the case of chloramphenicol, doxycycline, gentamicin and tetracycline. Both lactose-positive and lactose-negative strains were sensitive to colistin, neomycin, nitrofurantoin and nalidixic acid. They were resistant to ampicillin, cloxacillin, rifampicin, streptomycin, sulfatiazol and biseptol. Bacteriophage typing revealed that all lactose-negative strains isolated in this study from clinical samples belonged to the same phage pattern V. Lactose-positive strains belonged to two phage types VB and XI. Type VB prevailed.     

Risk of otitis externa after swimming in recreational fresh water lakes containing Pseudomonas aeruginosa.

OBJECTIVE--To determine whether an outbreak of otitis externa was due to bathing in recreational fresh water lakes and to establish whether the outbreak was caused by Pseudomonas aeruginosa in the water. DESIGN--Matched case-control study. SETTING--The Achterhoek area, the Netherlands. SUBJECTS--98 cases with otitis externa and 149 controls matched for age, sex, and place of residence. MAIN OUTCOME MEASURES--Odds ratios for type of swimming water and frequency of swimming; presence of P aeruginosa in ear swabs and fresh water lakes. RESULTS--Otitis externa was strongly associated with swimming in recreational fresh water lakes in the previous two weeks (odds ratio 15.5 (95% confidence interval) 4.9 to 49.2) compared with non-swimming). The risk increased with the number of days of swimming, and subjects with recurrent ear disease had a greatly increased risk. The lakes met the Dutch bathing water standards and those set by the European Commission for faecal pollution in the summer of 1994, but P aeruginosa was isolated from all of them, as well as from the ear swabs of 78 (83%) of the cases and 3 (4%) of the controls. CONCLUSIONS--Even when current bathing water standards are met, swimming can be associated with a substantial risk of otitis externa because of exposure to P aeruginosa. People with recurrent ear disease should take special care when swimming in waters containing P aeruginosa.     

Plasmid profile typing provides a method for the differentiation of strains of Salmonella enteritidis phage type 4 isolated in Turkey

Five phage types have been identified in 38 strains of Salmonella enteritidis isolated in Turkey in the 20-month period June 1992-January 1994. Strains belonging to phage type 4 predominated. Within phage type 4, plasmid profile typing has proved a useful method of strain discrimination and has confirmed the identity of a putative outbreak involving canteen workers in an industrial complex.     

Potential sources of the 1995 Venezuelan equine encephalitis subtype IC epidemic

Venezuelan equine encephalitis viruses (VEEV) belonging to subtype IC have caused three (1962-1964, 1992-1993 and 1995) major equine epizootics and epidemics. Previous sequence analyses of a portion of the envelope glycoprotein gene demonstrated a high degree of conservation among isolates from the 1962-1964 and the 1995 outbreaks, as well as a 1983 interepizootic mosquito isolate from Panaquire, Venezuela. However, unlike subtype IAB VEEV that were used to prepare inactivated vaccines that probably initiated several outbreaks, subtype IC viruses have not been used for vaccine production and their conservation cannot be explained in this way. To characterize further subtype IC VEEV conservation and to evaluate potential sources of the 1995 outbreak, we sequenced the complete genomes of three isolates from the 1962-1964 outbreak, the 1983 Panaquire interepizootic isolate, and two isolates from 1995. The sequence of the Panaquire isolate, and that of virus isolated from a mouse brain antigen prepared from subtype IC strain P676 and used in the same laboratory, suggested that the Panaquire isolate represents a laboratory contaminant. Some authentic epizootic IC strains isolated 32 years apart showed a greater degree of sequence identity than did isolates from the same (1962-1964 or 1995) outbreak. If these viruses were circulating and replicating between 1964 and 1995, their rate of sequence evolution was at least 10-fold lower than that estimated during outbreaks or that of closely related enzootic VEEV strains that circulate continuously. Current understanding of alphavirus evolution is inconsistent with this conservation. This subtype IC VEEV conservation, combined with phylogenetic relationships, suggests the possibility that the 1995 outbreak was initiated by a laboratory strain.     

Vero cytotoxin-producing Escherichia coli O157 in beefburgers linked to an outbreak of diarrhoea, haemorrhagic colitis and haemolytic uraemic syndrome in Britain

Vero cytotoxin (VT)-producing Escherichia coli O157 (0157 VTEC) were isolated from a raw beefburger obtained from a retail source linked to a small community outbreak of 0157 VTEC infection in Wales. Strains from the meat and from seven of eight patients belonged to phage type 49 and were indistinguishable by their VT-type, plasmid content and hybridization with DNA of a VT-encoding phage from an 0157 VTEC strain. This first report of the isolation of 0157 VTEC from a beef product in Britain supports the view that there is a bovine reservoir for this organism.     

Differentiation of Shigella strains by plasmid profile analysis, serotyping and phage typing

Ninety-one Shigella flexneri and 29 Shigella sonnei strains isolated during 1994 from sporadic cases of shigellosis and healthy carriers were analyzed for plasmid profile in order to compare the discriminating ability of this method with that of serotyping and phage typing. Our study revealed 10 plasmid profiles (PP) among S. sonnei strains. A total of 26 out of 29 (89%) S. sonnei isolates could be placed into two phage types (type 1 and 20) comprising four PP for phage type 1 and seven PP for type 20, respectively. Twenty-three different PP were identified among S. flexneri strains. Each serotype was associated with a specific predominant plasmid profile, except serotype 2a. This serotype, the most frequently isolated in Romania, was still rather homogeneous: 33 out of 39 isolates belonged to phage type 125, 27 of which could be placed into two related PP (F10 and F17). Comparison of plasmid patterns of epidemiologically independent S. flexneri serotype 2a isolates with those exhibited by 45 serotype 2a isolates associated to six independent outbreaks revealed the same homogeneity. Thirty-eight strains, representing 4 of 6 outbreaks, had F10 and F17 plasmid patterns. The discrimination indices (D) for plasmid profile analysis alone (D = 0.890) and for the combination of serotyping and phage typing (D = 0.841) indicate that both typing systems have a nearly similar ability of discriminating among S. flexneri strains. By combining the results of the three typing methods, a total of 42 types are distinguished and the D value is 0.942. Our data suggest that plasmid profile analysis can complement phenotyping methods resulting in a degree of discrimination that cannot be achieved by either system alone.     

The value of pyrolysis mass spectrometry to investigate nosocomial outbreaks caused by Serratia marcescens

Simultaneous outbreaks of S. marcescens infection going on in the Neonatal Intensive Care Unit and the Surgical Department of the same hospital were investigated by pyrolysis mass spectrometry (PyMS). The PyMS analysis of the strains clearly demonstrated that the two outbreaks were caused by different strains. The 14 S. marcescens isolates from the first outbreak were closely related, with the exception of one environmental isolate, which did not harbour the ESBL plasmid, which was present in all other isolates. However, the phage type of all 14 isolates was the same. Among the 9 S. marcescens isolates from the second outbreak, PyMS clearly distinguished 3 that exhibited gentamicin resistance from the remaining 6 gentamicin-susceptible isolates. Phage typing was unhelpful in this case, as none of the isolates were typable. The PyMS typing of nosocomial outbreak strains can reach the level of discrimination approaching that achieved by molecular genetic analysis.     

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.     

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.     

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.     

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.