Epidemiology of salmonellosis in garden birds in England and Wales, 1993 to 2003

Salmonellosis has been reported as an important cause of mortality of garden birds in several countries, including Norway and Scotland. We investigated the frequency of the disease in garden birds submitted for postmortem examination by members of the public in England and Wales between 1993 and 2003, inclusive. We found salmonellosis to be the most frequent cause of death due to infectious disease in the garden birds submitted. This disease was confirmed in 7 of the 45 bird species that were examined postmortem, with the greenfinch (Carduelis chloris) and the house sparrow (Passer domesticus) most frequently affected. Salmonella Typhimurium definitive phage type (DT) 40, DT56 variant(v), and DT160 accounted for the majority of isolates. Salmonellosis incidents chiefly occurred in the English Midlands, the English/Welsh border region, and southern England. Variation in the temporal and spatial distribution of the phage types occurred over the study period. While birds were examined throughout the year, there was a marked winter seasonality in salmonellosis. A significant sex bias was observed in affected greenfinches, with males more frequently diagnosed with salmonellosis than females. No sex bias was observed for other affected species. Further research is required to determine if salmonellosis is an important constraint to the populations of affected species and if disease outbreaks are driven by human factors, such as provisioning.

Public health investigations of Salmonella Enteritidis in catering raw shell eggs, 2002-2004

AIMS

In response to a dramatic change in the epidemiology of Salmonella Enteritidis in England and Wales thought to be associated with raw shell eggs, the Health Protection Agency initiated public health investigations to establish the incidence of Salmonella contamination and origin of eggs used by catering premises implicated in outbreaks of Salm. Enteritidis.

METHODS AND RESULTS

Between October 2002 and November 2004, 16 971 eggs were sampled and Salmonella were recovered from 3.4%. Salmonella was isolated from 5.5% and 6.3% of Spanish and eggs of unknown origin, respectively, used in catering premises linked to outbreaks, a level significantly higher than that (1.1%) found in nonLion Quality UK eggs sampled. The small sample of UK Lion Quality eggs tested (reflecting their lack of use in premises visited) did not contain Salmonella. Several phage types of Salm. Enteritidis other than phage type 4 (PT 4) were identified with nonUK eggs.

CONCLUSIONS

Eggs from Spain were implicated as a major source of infection. Eggs were contaminated more frequently with Salmonella when shells were dirty and/or cracked, and stored at above 8 degrees C.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of Spanish eggs by the catering sector has been identified as a consistent significant factor in many of the outbreaks caused by Salm. Enteritidis nonPT4 in England and Wales during 2002-2004. Advice to caterers and hospitals that raw shell eggs should not be used in food that will either not be cooked or only lightly cooked should be reinforced.

Foodborne general outbreaks of Salmonella Enteritidis phage type 4 infection, England and Wales, 1992-2002: where are the risks?

Foodborne outbreaks of Salmonella enterica serovar Enteritidis phage type 4 (PT4) infection (n=497), reported to the Health Protection Agency Communicable Disease Surveillance Centre between 1992 and 2002, were compared with other pathogens (n=1148) to determine factors (season, setting, food vehicles, food safety faults) associated with this pathogen. Logistic regression was applied to control for potential confounding. Foodborne general outbreaks of S. Enteritidis PT4 infection were more likely to occur in the spring and summer, and were more often linked to schools, private residences and residential institutions. Eggs, egg products and the use of raw shell egg were strongly associated with this pathogen. Most outbreaks were linked to cross-contamination and inadequate heat treatment. This paper describes the decline in the S. Enteritidis PT4 epidemic, providing evidence that control measures introduced, e.g. improved biosecurity and vaccination, have worked. Continued surveillance of human and veterinary salmonellosis is essential to detect future problems.

Multiple antimicrobial resistant Salmonella enterica serovar Paratyphi B variant Java in cattle: a case report

An epidemiological investigation of a calf rearing premises and a closely associated dairy herd was carried out after the isolation of Salmonella enterica serovar Paratyphi B variant Java phage type 3b variant 2 from clinically diseased calves on the premises. The isolate was resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides, tetracyclines, trimethoprim and cefoperazone. The organism was widespread on the calf unit and was also recovered from the dairy premises, mainly from groups of weaned calves. The investigation was extended to 10 epidemiologically linked farms but no S Java was isolated from any of the 40 to 60 samples collected from each premises. Molecular studies showed that the S Java isolates were genetically most similar to isolates from cases of human disease associated with ornamental fish tanks or feed. Long PCR and resistance gene profiling identified a resistance island which was indistinguishable from the human 'fish tank' strain of S Java and animal and human epidemic strains of S Typhimurium DT104. The isolates were clearly distinguished from multi-resistant S Java strains commonly associated with continental poultry. This is the first report of S Java with this resistance pattern in Great Britain.

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.

Molecular characterisation of an outbreak strain of multiresistant Salmonella enterica serovar Typhimurium DT104 in the UK

A major national outbreak of multiresistant Salmonella enterica serovar Typhimurium definitive phage type 104 (MR DT104) occurred in England and Wales in the summer of 2000. Isolates of MR DT104 were characterised by antimicrobial resistance type (R-type), pulsed-field gel electrophoresis (PFGE), plasmid profiling and fluorescent amplified fragment length polymorphism (fAFLP) analysis. Results of R-type, PFGE and fAFLP showed that summer 2000 outbreak-associated isolates were indistinguishable from most MR DT104 isolates collected in England and Wales during the 1980s and 1990s. However, outbreak-associated isolates all had an additional 2-MDa plasmid (PP D), and this distinct profile allowed outbreak cases to be distinguished from background MR DT104 infections, thereby facilitating the epidemiological investigation by improving the specificity of the case definition. The study demonstrated the highly clonal nature of MR DT104 and the importance of a hierarchical approach to molecular subtyping for outbreak investigations.

A comparison of antimicrobial susceptibilities in nontyphoidal salmonellas from humans and food animals in England and Wales in 2000

A joint study by the Public Health Laboratory Service and the Veterinary Laboratories Agency of resistance to antimicrobials in isolates of Salmonella enterica serotypes Enteritidis, Typhimurium, Hadar, and Virchow from humans and food-producing animals in England and Wales in 2000 has demonstrated that resistance was most common in Typhimurium, particularly in strains of definitive phage type (DT) 104. However resistance was also common in other phage types, particularly DTs 193 and 208 and phage type U302. Multiresistant strains of DT208 appeared to be predominantly associated with pigs; for the other phage types, the human/food-producing animal relationships of drug-resistant isolates were more complex. For Enteritidis, Virchow, and Hadar, there were substantial differences in the resistance spectra of isolates from humans and food-producing animals, suggesting that food-producing animals bred in England and Wales may not be the primary sources of drug-resistant strains of these serotypes causing infections in humans. Further phenotypic and molecular comparison of drug-resistant isolates of these serotypes may be required to ascertain the sources of strains responsible for infections in humans.

LightCycler gyrA mutation assay (GAMA) identifies heterogeneity in GyrA in Salmonella enterica serotypes Typhi and Paratyphi A with decreased susceptibility to ciprofloxacin

Mutations in gyrA in strains of Salmonella enterica serotypes Typhi and Paratyphi A have been characterised by a LightCycler-based PCR-hybridisation gyrA mutation assay (GAMA) and by DNA sequencing. Four mutations (Ser-83 to Phe, Asp-87 to Asn, Ser-83 to Tyr and Asp-87 to Gly) have been identified in 13 strains of Typhi and three strains of Paratyphi A resistant to nalidixic acid (=nal(r)) and with decreased susceptibility to ciprofloxacin (=Cp(L)), with the mutation Ser-83 to Phe predominating. The results have demonstrated heterogeneity in gyrA in nal(r) Cp(L) strains of Typhi and Paratyphi A and may be useful for epidemiological investigations. No mutations in gyrA were identified in four Cp(L) strains of S. Typhi that were sensitive to nalidixic acid. The mechanism of decreased susceptibility to ciprofloxacin in these strains is under investigation.

A European outbreak of Salmonella enterica serotype Typhimurium definitive phage type 204b in 2000

OBJECTIVE

To describe the clinical, epidemiologic and microbiological features of a large outbreak of infection with a multiresistant Salmonella enterica serotype Typhimurium definitive type DT204b infection involving at least 392 people in five European countries.

METHODS

Icelandic public-health doctors responded to a report on an Internet news site of an outbreak of infection with a multiresistant strain of Typhimurium DT104 in England by contacting the Public Health Laboratory Service (PHLS) Communicable Disease Surveillance Centre (CDSC). An international alert was sent out through Enter-net. All strains from England & Wales, The Netherlands, Scotland and Germany, and 17 of the outbreak isolates from Iceland, were phage-typed, screened for antimicrobial resistance, and subjected to molecular typing. Hypothesis-generating interviews were conducted, followed by case-control studies performed in Iceland and England.

RESULTS

Isolates from cases in Iceland, England and Wales, The Netherlands, Scotland and Germany were identified as Typhimurium DT204b. The antimicrobial resistance pattern was ACGNeKSSuTTmNxCpL. All strains tested displayed an identical plasmid profile. Strains from five cases in England & Wales and five cases in Iceland possessed identical pulsed-field profiles. Although a common source was suspected, only Iceland implicated imported lettuce as a vehicle, with an analytic epidemiologic study (OR = 40.8; P = 0.005; 95% CI 2.7-3175).

CONCLUSION

The identification of international outbreaks, necessary for investigation and control, can be facilitated by standardized phage-typing techniques, the electronic transfer of molecular typing patterns, formal and informal links established through international surveillance networks, and the early reporting of national outbreaks to such networks.

A national outbreak of multi-resistant Salmonella enterica serovar Typhimurium definitive phage type (DT) 104 associated with consumption of lettuce

Between 1 August and 15 September 2000, 361 cases of Salmonella enterica serotype Typhimurium definitive phage type (DT) 104, resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides, spectinomycin and tetracycline (R-type ACSSuSpT), were identified in England and Wales residents. Molecular typing of 258 isolates of S. Typhimurium DT104 R-type ACSSuSpT showed that, although isolates were indistinguishable by pulsed-field gel electrophoresis, 67% (174/258) were characterized by a particular plasmid profile. A statistically significant association between illness and consumption of lettuce away from home was demonstrated (OR = 7.28; 95% CI=2.25-23.57; P=0.0006) in an unmatched case-control study. Environmental investigations revealed that a number of food outlets implicated in the outbreak had common suppliers of salad vegetables. No implicated foods were available for microbiological testing. An environmental audit of three farms that might have supplied salad vegetables to the implicated outlets did not reveal any unsafe agricultural practices. The complexity of the food supply chain and the lack of identifying markers on salad stuffs made tracking salad vegetables back to their origin extremely difficult in most instances. This has implications for public health since food hazard warnings and product withdrawal are contingent on accurate identification of the suspect product.

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.

Combination of pulsed-field gel electrophoresis (PFGE) and single-enzyme amplified fragment length polymorphism (SAFLP) for differentiation of multiresistant Salmonella enterica serotype typhimurium

OBJECTIVE

To assess the combined application of plasmid profile typing, pulsed-field gel electrophoresis (PFGE) and PCR-based single-enzyme amplified fragment length polymorphism (SAFLP) for the differentiation of 18 multiresistant (MR) and one drug-sensitive strain of Salmonella enterica serotype typhimurium from humans and food animals.

METHODS

Strains were phage typed and tested for resistance to a panel of antimicrobial agents. Strains were also tested for the ability to transfer resistance either directly or by mobilization to standard strains of Escherichia coli K12. Plasmid DNA was extracted from both drug-resistant donor strains and from drug-resistant exconjugants. Total genomic DNA was characterized by PFGE following digestion with the restriction endonuclease XbaI. The resultant patterns were categorized and analyzed by dendrogram analysis using the Dice coefficient and by data clustering using unweighted pair-group arithmetic averaging (UPGMA). Isolates were also characterized and categorized by SAFLP. The levels of discrimination achieved by each method were assessed individually and in combination.

RESULTS

Plasmid DNA was detected in all of the 18 MR isolates but, not in the drug-sensitive isolate. Using PFGE, 19 different profiles were identified, falling into eight major categories. However, by SAFLP, only eight profiles were observed. Subsequent investigations have demonstrated epidemiologic relationships within at least one of these SAFLP profile groupings.

CONCLUSIONS

These studies have demonstrated that PFGE and SAFLP can be used independently for the differentiation of MR S. Typhimurium from humans and food animals. However, when used in combination, SAFLP can provide a format for broad epidemiologic groupings. These groupings can be further subdivided by PFGE to provide detailed information on putative strain relationships at the genotypic level.

Effect of challenge temperature and solute type on heat tolerance of Salmonella serovars at low water activity

Salmonella spp. are reported to have an increased heat tolerance at low water activity (a(w); measured by relative vapor pressure [rvp]), achieved either by drying or by incorporating solutes. Much of the published data, however, cover only a narrow treatment range and have been analyzed by assuming first-order death kinetics. In this study, the death of Salmonella enterica serovar Typhimurium DT104 when exposed to 54 combinations of temperature (55 to 80 degrees C) and a(w) (rvp 0.65 to 0.90, reduced using glucose-fructose) was investigated. The Weibull model (LogS = -bt(n)) was used to describe microbial inactivation, and surface response models were developed to predict death rates for serovar Typhimurium at all points within the design surface. The models were evaluated with data generated by using six different Salmonella strains in place of serovar Typhimurium DT104 strain 30, two different solutes in place of glucose-fructose to reduce a(w), or six low-a(w) foods artificially contaminated with Salmonella in place of the sugar broths. The data demonstrate that, at temperatures of > or =70 degrees C, Salmonella cells at low a(w) were more heat tolerant than those at a higher a(w) but below 65 degrees C the reverse was true. The same patterns were generated when sucrose (rvp 0.80 compared with 0.90) or NaCl (0.75 compared with 0.90) was used to reduce a(w), but the extent of the protection afforded varied with solute type. The predictions of thermal death rates in the low-a(w) foods were usually fail-safe, but the few exceptions highlight the importance of validating models with specific foods that may have additional factors affecting survival.

General outbreaks of infectious intestinal disease linked with poultry, England and Wales, 1992-1999

Between 1992 and 1999, 1426 foodborne general outbreaks of infectious intestinal disease (IID) were reported to the Public Health Laboratory Service Communicable Disease Surveillance Centre. A fifth were associated with the consumption of poultry. Chicken was implicated in almost three quarters of these outbreaks, turkey in over a fifth and duck in 2% of outbreaks. The organisms most frequently reported were Salmonella (30% of outbreaks), Clostridium perfringens (21%) and Campylobacter (6%). Over 7000 people were affected, with 258 hospital admissions and 17 deaths. During the summer, outbreaks were mainly of salmonellosis and attributed to the consumption of chicken. In December, C. perfringens and turkey were the organism and vehicle most often implicated. Most outbreaks occurred on commercial catering premises (56%) or in private houses (21%). The highlight of this surveillance period was the fall in outbreaks of salmonellosis linked with poultry products, probably due, at least in part, to the vaccination of poultry flocks.

Variation in clonality and antibiotic-resistance genes among multiresistant Salmonella enterica serotype typhimurium phage-type U302 (MR U302) from humans, animals, and foods

Since 1990 multiresistant (MR) Salmonella enterica serotype Typhimurium definitive phage-type (DT) 104 (MR DT104) and closely related phage types have emerged as a worldwide health problem in humans and food animals. In this study the presence of the blaCARB-2 (ampicillin), cmlA (chloramphenicol), aadA2 (streptomycin/spectinomycin), sul1 (sulphonamide), and tetG (tetracycline) resistance genes in isolates of one such phage type, U302, have been determined. In addition blaTEM primers have been used for the detection of TEM-type beta-lactamases. Isolates have also been characterized by plasmid profile and pulsed field gel electrophoresis (PFGE). Thirty-three of 39 isolates were positive for blaCARB-2, cmlA, aadA2, sul1 and tetG, four for blaTEM, aadA2 and sul1, one for aadA2 and sul1, and one for blaTEM only. blaTEM-mediated ampicillin resistance was transferred to Escherichia coli K12 from three isolates along with other resistance markers, including resistance to chloramphenicol, streptomycin, spectinomycin, sulphonamides, and tetracyclines. Strains carried up to 6 plasmids and 34 plasmid profiles were identified. Although the majority of strains (33/39) produced a PFGE profile identical to that predominant in MR DT104, six different patterns were generated demonstrating the presence of various clones within MR U302. The results show that the majority of the MR U302 strains studied possessed the same antibiotic resistance genes as MR DT104. However, isolates with distinctive PFGE patterns can have different mechanisms of resistance to ampicillin, chloramphenicol, streptomycin, sulphonamides, and tetracyclines. Such resistance genes may be borne on transmissible plasmids.

Antimicrobial drug resistance in non-typhoidal salmonellas from humans in England and Wales in 1999: decrease in multiple resistance in Salmonella enterica serotypes Typhimurium, Virchow, and Hadar

In 1999 the incidence of multiple drug resistance (to four or more antimicrobials) in non-typhoidal salmonellas from humans in England and Wales fell in isolations of Salmonella enterica serotypes Typhimurium, Virchow, and Hadar. This fall has been most noticeable in S. Typhimurium, where 59% of isolates were multiresistant compared to 81% in 1996. The main reason for this has been a 75% decline in isolations of multiply-resistant S. Typhimurium definitive phage type (DT) 104 (MR DT104) since 1996. Nevertheless MR DT104 remains second to S. Enteritidis phage type 4 as the most common strain in cases of human salmonellosis in England and Wales. Multiple resistance has also remained high in S. Hadar, with 49% of isolates resistant to four drugs or more compared to 56% in 1996. Isolates with decreased sensitivity to ciprofloxacin (minimal inhibitory concentration: 0.25-1.0 mg/L) have increased in incidence in S. Enteritidis, S. Virchow, and S. Hadar; in S. Hadar 70% of isolates were resistant to ciprofloxacin at this level. It is hoped that Codes of Practice introduced by some pharmaceutical companies, governments, professional organisations, and others to combat the unnecessary prophylactic use of fluoroquinolones in animal husbandry will not result in a reduction in the incidence of resistance to ciprofloxacin in salmonella organisms causing infections in humans.

Use of a LightCycler gyrA mutation assay for rapid identification of mutations conferring decreased susceptibility to ciprofloxacin in multiresistant Salmonella enterica serotype Typhimurium DT104 isolates

A LightCycler-based PCR-hybridization gyrA mutation assay (GAMA) was developed to rapidly detect gyrA point mutations in multiresistant (MR) Salmonella enterica serotype Typhimurium DT104 with decreased susceptibility to ciprofloxacin (MIC, 0.25 to 1.0 mg/liter). Ninety-two isolates (49 human, 43 animal) were tested with three individual oligonucleotide probes directed against an Asp-87-to-Asn (GAC-->AAC) mutation, an Asp-87-to-Gly (GAC-->GGC) mutation, and a Ser-83-to-Phe (TCC-->TTC) mutation. Strains homologous to the probes could be distinguished from strains that had different mutations by their probe-target melting temperatures. Thirty-seven human and 30 animal isolates had an Asp-87-to-Asn substitution, 6 human and 6 animal isolates had a Ser-83-to-Phe substitution, and 5 human and 2 animal isolates had an Asp-87-to-Gly substitution. The remaining six strains all had mismatches with the three probes and therefore different gyrA mutations. The sequencing of gyrA from these six isolates showed that one human strain and two animal strains had an Asp-87-to-Tyr (GAC-->TAC) substitution and two animal strains had a Ser-83-to-Tyr (TCC-->TAC) substitution. One animal strain had no gyrA mutation, suggesting that this isolate had a different mechanism of resistance. Fifty-eight of the strains tested were indistinguishable by several different typing methods including antibiograms, pulsed-field gel gel electrophoresis, and plasmid profiling, although they could be further subdivided according to gyrA mutation. This study confirmed that MR DT104 with decreased susceptibility to ciprofloxacin from humans and food animals in England and Wales may have arisen independently against a background of clonal spread of MR DT104.

Decreased susceptibility to ciprofloxacin in Salmonella enterica serotype typhi, United Kingdom

In 1999, 23% of Salmonella enterica serotype Typhi isolates from patients in the United Kingdom exhibited decreased susceptibility to ciprofloxacin (MIC 0.25-1.0 mg/L); more than half were also resistant to chloramphenicol, ampicillin, and trimethoprim. Increasing numbers of treatment failures have been noted. Most infections have been in patients with a recent history of travel to India and Pakistan.

The emergence and spread of antibiotic resistance in food-borne bacteria

Since the early 1990s there has been a dramatic increase in resistance to antimicrobial drugs in Salmonella enterica and Campylobacter spp., and to a lesser extent in Vero cytotoxin-producing Escherichia coli O157 from cases of human infection in developed countries. For S. Typhimurium a particularly important aspect of this increase has been the widespread dissemination of a multiply drug-resistant (MR) strain of definitive phage type (DT) 104 in food animals since the early 1990s. The use of antimicrobials for prophylaxis in food producing animals has been an important factor in the emergence of strains with resistance to certain antimicrobials. It is hoped that recently introduced Codes of Practice for the prophylactic use of antimicrobials in food animals will result in a decline in the occurrence of drug resistant strains in the food chain.

Spread of resistance from food animals to man--the UK experience

Since 1990 there have been dramatic increase in the occurrence multiply drug-resistant strains of zoonotic pathogens causing infections in humans in many developed countries. Of particular note has been the epidemic spread of MR strains of S. typhimurium DT 104, which now appear to have an almost world-wide distribution. Within DT104 the increasing spectrum of resistance is of considerable concern, with strains with decreased susceptibility to ciprofloxacin increasing in incidence in the United Kingdom and also causing serious disease in humans in other countries. For campylobacters the incidence of ciprofloxacin-resistant organisms is also increasing, with reports of such isolates from numerous countries throughout the world. For VTEC O157, although resistance is increasing, multiple resistance and resistance to ciprofloxacin remains rare. Drug resistance in food-borne pathogens is an unfortunate but almost inevitable consequence of the use of antimicrobials in food animals. Although for some pathogens--e.g., Campylobacter spp., the use of antimicrobials in human medicine is also an important factor (Smith el al 1999), it is the use of antimicrobials in food animals which has been a major factor in the development of decreased susceptibility to antibiotics such as ciprofloxacin in zoonotically-transmitted salmonellas. Such use is quite legitimate. However it is regrettable that recommendations such as propounded in 1992 in the UK by the Expert Group on Animal Feedingstuffs--the Lamming Committee, that any new antibiotics with cross resistance to those used in human medicine should not be used for prophylaxis in animal husbandry, were not accepted (Anonymous, 1992). Although the clock cannot be turned back, to combat the development of resistance to such important drugs as the fluoroquinolones it is hoped that a Code of Practice for their use in food animals will soon be internationally implemented.

Increase in multiple antibiotic resistance in nontyphoidal salmonellas from humans in England and Wales: a comparison of data for 1994 and 1996

The incidence of multiple drug resistance (to four or more antimicrobials) in salmonellas from humans in England and Wales in 1996 has been compared with corresponding data for 1994. For Salmonella enteritidis multiple resistance has remained rare, although a high proportion of isolates of phage type 6A have shown resistance to ampicillin. For S. typhimurium multiple resistance has continued to increase, with 81% of isolates now multiresistant. Of particular importance in S. typhimurium has been the continued epidemic of multiresistant DT 104 and the increasing occurrence of strains of this phage type with additional resistance to trimethoprim and/or ciprofloxacin. For S. virchow, a 10% increase in multiple resistance is mainly concentrated in two phage types common in returning travellers. For S. hadar, there has been a substantial increase in the incidence of multiple resistance with over 50% of isolates now multiresistant. Substantial increases in the incidence of resistance to ciprofloxacin in multiresistant S. typhimurium DT 104, S. virchow, and S. hadar since 1993, when the fluoroquinolone antibiotic enrofloxacin was licensed for veterinary use in the UK, are of particular concern.

Harmonization of antibiotic susceptibility testing for Salmonella: results of a study by 18 national reference laboratories within the European Union-funded Enter-net group

For the effective surveillance of antimicrobial drug resistance within Salmonella organisms from humans, harmonization of methods used for sensitivity testing by laboratories responsible for the typing of such organisms is essential. A study of resistance or sensitivity to a panel of 11 antimicrobials by the Enter-net international surveillance network was therefore undertaken. There are 18 national Salmonella reference laboratories within this European Union-funded network. Forty-eight strains of Salmonella enterica were distributed to each laboratory for testing for resistance or sensitivity to ampicillin, cefotaxime, chloramphenicol, gentamicin, kanamycin, streptomycin, sulfonamides, tetracyclines, trimethoprim, nalidixic acid, and ciprofloxacin. Over 8,500 tests were assessed involving disk diffusion (DD), agar breakpoint (BP), or full minimum inhibitory concentration (MIC). Results indicated that whichever method was used, there was a high degree of concordance for the detection of resistance to most antimicrobials; only for decreased sensitivity to ciprofloxacin was there substantial nonconcordance. Because all isolates with decreased sensitivity to ciprofloxacin were resistant to nalidixic acid, it is suggested that, if required, MICs to ciprofloxacin could be determined for isolates resistant to nalidixic acid. For the detection of sensitivity, the main area of nonconcordance was in the detection of sensitivity to streptomycin. With the exception of decreased sensitivity to ciprofloxacin, we are confident that a database of antimicrobial susceptibilities can now be established and harmonized antibiogram data for Salmonella can now be exchanged for national Salmonella reference laboratories within the European Union.

Multiple clones within multidrug-resistant Salmonella enterica serotype Typhimurium phage type DT104. The Greek Nontyphoidal Salmonella Study Group

Six distinct clones were present among Greek multidrug-resistant Salmonella enterica serotype Typhimurium phage type DT104, since isolates belonging to resistance phenotypes including the ACSSuT (ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline) core could be distinguished with respect to their pulsed-field gel electrophoresis patterns, int1 integron structures, and presence or absence of antibiotic resistance genes ant(3'')-Ia, pse-1, and tem-1.

Pulsed field gel electrophoresis identifies an outbreak of Salmonella enterica serotype Montevideo infection associated with a supermarket hot food outlet

In February 1996 Salmonella enterica serotype Montevideo infection in a patient in the North Tyneside area was attributed to consumption of cooked chicken bought from a supermarket hot food outlet. Isolates from the patient, leftover food, and environmental samples were indistinguishable by pulsed field gel electrophoresis (PFGE). PFGE also demonstrated that an outbreak of infection with S. Montevideo associated with the hot food outlet had occurred in late 1995 and early 1996. This study shows the importance of microbial strain discrimination in outbreak investigations and illustrates the value of close liaison between microbiologists, epidemiologists, and environmental health officers in the control of salmonella outbreaks.

An immunoblotting procedure comprising O = 9,12 and H = d antigens as an alternative to the Widal agglutination assay

AIMS

To compare the established Widal agglutination assay with an immunoblotting procedure.

METHODS

110 sera were used to compare the established Widal agglutination assay with an immunoblotting procedure incorporating lipopolysaccharide (LPS) (O = 9,12) and flagellar (H = d) antigens.

RESULTS

Antibodies to the LPS antigens were detected in 18 sera by the Widal assay and in 37 by immunoblotting. Antibodies to the flagellar antigens were detected in 27 sera by Widal assay and in 25 by immunoblotting.

CONCLUSIONS

An immunoblotting procedure incorporating O = 9,12 LPS and H = d flagellar antigens was rapid and more sensitive than the established Widal agglutination assay for providing evidence of infection with S typhi.

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.

Molecular fingerprinting defines a strain of Salmonella enterica serotype Anatum responsible for an international outbreak associated with formula-dried milk

Molecular analyses based on plasmid profile typing and pulsed-field gel electrophoresis have defined a strain of Salmonella enterica serotype Anatum associated with the consumption of a particular brand of formula-dried milk responsible for an outbreak in late 1996/early 1997 involving 15 infants and 2 relatives in the UK, and 2 infants in France. The study has demonstrated the value of laboratory-based surveillance involving identification of the outbreak strain at the molecular level coupled with food microbiology and targeted epidemiological investigations, and has highlighted the importance of rapid communication and subsequent international collaboration through the European Union-funded Salm-Net salmonella surveillance network.

National outbreak of Salmonella senftenberg associated with infant food

Eight cases of Salmonella senftenberg infection in infants were identified in the first half of 1995 in England, five were indistinguishable S. senftenberg strains. A case-control study showed an association between illness and consumption of one brand of baby cereal (P = 0.03). The cereal manufacturer reported isolating S. senftenberg in June 1994 from an undistributed cereal batch. Outbreak strains and the cereal strain were all plasmid-free in contrast to other human isolates of S. senftenberg in the same period. Changes in the production process were implemented to prevent further contamination. Surveillance centres should strengthen the detection and investigation of outbreaks of gastrointestinal infection in susceptible groups, especially young children. In this outbreak, the study of only five cases led to identification of the vehicle of infection. Even when few cases are reported, epidemiological investigation in conjunction with molecular typing may lead to public health action which prevents continuing or future outbreaks.

Molecular fingerprinting of multidrug-resistant Salmonella enterica serotype Typhi

For epidemiologic investigations, the primary subdivision of Salmonella Typhi is vi-phage typing; 106 Vi-phage types are defined. For multidrug-resistant strains the most common types have been M1 (Pakistan) and E1 (India, Pakistan, Bangladesh, and the Arabian Gulf); a strain untypable with the Vi phages has been responsible for a major epidemic in Tajikistan. Most often, isolates from the Indian subcontinent have been resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, tetracyclines, and trimethoprim; but in the 1997 Tajikistan outbreak, the epidemic strain was also resistant to ciprofloxacin. For multidrug-resistant strains, subdivision within phage type can be achieved by plasmid profile typing and pulsed-field gel electrophoresis.

Resistance to ciprofloxacin in pathogenic Enterobacteriaceae in England and Wales in 1996

In 1996, 6% of Escherichia coli from extraintestinal infections were resistant to ciprofloxacin with minimum inhibitory concentrations (MICs) > or = 2 mg/l (high level resistance). Low level resistance (MIC 0.125-1 mg/l) was also identified in 7% of Salmonella typhi, 4% of S paratyphi A, and 4% of non-typhoidal salmonellas. However, resistance to ciprofloxacin was rarely identified in shigellas. For E coli, physicians should be aware that treatment failures may occur when patients with invasive illness are treated with ciprofloxacin before the results of laboratory sensitivity tests are available. For salmonellas an increasing number of treatment failures have been recorded for patients infected with strains with low level resistance. Because of the increasing incidence of Enterobacteriaceae with low level resistance to ciprofloxacin, it is recommended that for this group of organisms a breakpoint of 0.125 mg/l should be included in laboratory sensitivity tests.

Application of molecular methods to a nosocomial outbreak of Salmonella enteritidis phage type 4

A nosocomial outbreak of Salmonella enteritidis phage type 4 occurred in July 1995. Seven definite cases were identified over 13 days affecting four wards in a London hospital. The outbreak strain was characterized by plasmid profile typing and pulsed-field gel electrophoresis (PFGE), and was unusual in that it did not possess a 38 MDa plasmid common to most isolates of S. enteritidis PT 4 made from humans and food animals in England and Wales. Seven asymptomatic excreters were identified on screening. No additional cases occurred on wards after standard isolation procedures were implemented. No common or continuing food or dietary source was identified. Results of epidemiological, microbiological and environmental investigations suggested that the outbreak was due to person-to-person transmission within the hospital. The source of the outbreak was not established but was probably due to admission of a patient with an unrecognized infection of S. enteritidis PT 4. The study highlights the importance of close collaboration between hospital staff, epidemiologists and microbiologists, and demonstrates the value of molecular techniques for strain subdivision in outbreak investigations.

Multidrug-resistant Salmonella typhi: a worldwide epidemic

Since 1989, strains of Salmonella typhi resistant to chloramphenicol, ampicillin, and trimethoprim (i.e., multidrug-resistant [MDR] strains) have been responsible for numerous outbreaks in countries in the Indian subcontinent, Southeast Asia, and Africa. MDR strains have also been isolated with increasing frequency from immigrant workers in countries in the Arabian Gulf, as well as in developed countries from returning travelers. In all MDR strains so far examined, multiple resistance has been encoded by plasmids of the H1 incompatibility group. As a result of the widespread dissemination of such strains, chloramphenicol can no longer be regarded as the first-line drug for typhoid fever. Because strains are also resistant to ampicillin and trimethoprim, the efficacy of these antibiotics has also been impaired, and ciprofloxacin is now the drug of choice for typhoid fever. Chromosomally encoded resistance to ciprofloxacin has now been observed in a small number of strains isolated in the United Kingdom from patients returning from the Indian subcontinent, and in at least one case the patient did not respond to treatment with this antibiotic. It is regrettable that resistance to ciprofloxacin has now emerged in MDR S. typhi, and it is of paramount importance to limit the unnecessary use of this vital drug so that its efficacy should not be further jeopardized.

Plasmid characterization and pulsed-field electrophoretic analysis demonstrate that ampicillin-resistant strains of Salmonella enteritidis phage type 6a are derived from Salm. enteritidis phage type 4

Plasmid incompatibility studies have demonstrated that strains of Salmonella enteritidis phage type (PT) 6a resistant to ampicillin possess a 36 megadalton incompatibility group (Inc) X plasmid coding for resistance to ampicillin which is capable of converting strains of Salm. enteritidis belonging to PTs 1 and 4 to PT 6a, and PT 8 to PT 13. However, pulsed-field gel electrophoresis (PFGE) has demonstrated that all clinical isolates of PT 6a have a characteristic XbaI pulsed-field profile which is distinct from that of PT 1 and which can only be differentiated from that of PT 4 by the presence of plasmid-associated fragments of less than 45 kb. It is concluded that ampicillin-resistant strains of Salm. enteritidis PT 6a are derived from strains of Salm. enteritidis PT 4 by acquisition of an Inc X ampicillin resistance plasmid.

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.

Epidemiological application of differentiating multiresistant Salmonella typhimurium DT104 by plasmid profile

Human isolates of multiresistant Salmonella typhimurium definitive phage type (DT) 104 in England and Wales are currently second in number only to those of S. enteritidis phage type 4. Differentiation of strains is essential in epidemiological investigations and the value of one method, plasmid profile typing, has been assessed in a study of 600 isolates of S. typhimurium DT 104 with multiresistant antibiograms (R-types) ACSSuT, ACSSuTCp and ACSSuTTm from humans, food animals, human food, pets, and animal feed made in England and Wales from January 1990 to April 1996. Twenty plasmid profile (PP) types have been identified in isolates of R-type ACSSuT and ACSSuTCp. One profile type, with a single plasmid of 60 megadaltons-PP type A-has predominated, but identification of PP type has proved useful in some epidemiological investigations. A further four PP types have been identified in isolates of DT 104 R-type ACSSuTTm, in which resistance to trimethoprim is encoded by a plasmid of 4.6 megadaltons and the two commonest PP types are related to those also common in DT 104 R-type ACSSuT. Methods of differentiating within the commonest profile type are now needed.

Salmonella virchow PT 26 infection in England and Wales: a case control study investigating an increase in cases during 1994

An increase in the number of human isolates of Salmonella virchow phage type (PT) 26 in England and Wales during 1994 was investigated. A national case control study was conducted which included 88 cases and 182 controls. The cases were mostly young adults (median age 26) and 13 (15%) were admitted to hospital. Acquisition of S. virchow PT 26 was associated with the consumption of any chicken (OR 2.5, CI 1.1-5.8), of chicken curry from restaurants and take aways (OR 2.9, CI 1.4-6.1), and of some other diverse types of pre-prepared chicken (OR 3.8, CI 1.9-7.6). Halal chicken was associated (P = 0.006) with illness in a subset. There were negative associations with contact with animals (OR 0.47, CI 0.23-0.95) and with the consumption of chicken cooked whole (OR 0.37, CI 0.21-0.66). The increase in S. virchow PT 26 may be due to changing epizoology and may be an indicator of what will become the dominant salmonella strain in poultry in future years. The increasing incidence of S. virchow PT 26 is of particular concern because of its association with more invasive disease in humans.

Outbreaks of salmonellosis in hospitals in England and Wales: 1992-1994

Data from the surveillance scheme of general outbreaks of infectious intestinal disease in England and Wales were used to describe the epidemiology of outbreaks of salmonellosis in hospitals from 1992-1994. Outbreaks of infectious intestinal disease in hospitals accounted for 15% (189/1275) of all outbreaks. A salmonella was the implicated pathogen in 12% (22/189). The mode of transmission was described as mainly person to person in 12 outbreaks, mainly foodborne in eight and equal or unknown proportions of foodborne and person to person in two. The most common strain involved was Salmonella enteritidis PT4 (11 outbreaks). The mean duration of outbreaks was 16 days. The mean attack rate in patients was 25% but varied from 2-67%. Illness was reported in 260 patients, of whom 130 had a laboratory confirmed infection. Eight hundred and twenty-six asymptomatic patients were tested, 31 of whom were positive. The salmonella infection was believed to have contributed to the deaths of five patients. Ill staff (115) were tested and 68 were positive; 1508 well staff were tested and 33 were positive. Outbreaks of salmonellosis in hospitals are preventable. Attack rates can be high and outbreaks are often prolonged, with high morbidity and associated disruption of hospital services. There is need for effective infection control policies, appropriate training of staff, simple surveillance systems and readily available expert advice to ensure outbreaks are rapidly controlled.