Hospital outbreak of salmonella virchow possibly associated wit a food handler

Journal of Hospital Infection (2000) 44: 261–266
doi:10.1053/Jhin.1999.0712, available online at on
Hospital outbreak of Salmonella virchow
possibly associated with a food handler
H. Maguire*, P. Pharoah†, B.Walsh‡, C. Davison§, D. Barrie¶, E. J.Threlfall** andS. Chambers†† * PHLS/South Thames, Regional Epidemiology Unit, St George’s Hospital, Blackshaw Road, London SW17 OQT,UK,† Institute of Public Health, Robinson Way, Cambridge CB2 2SR, ‡Department of Public Health Medicine,Kingston & Richmond Health Authority, 22 Hollyfield Road, Surbiton KT5 9AL, §Environmental HealthDepartment, Royal Borough of Kingston upon Thames, Guildhall 2, Kingston Upon Thames, Surrey KT1 1EU,¶Department of Medical Microbiology, Charing Cross and Westminster Medical School, Fulham Palace Road,London W6 8RF, **Laboratory of Enteric Pathogens (LEP), Central Public Health Laboratory (CPHL)61, Colindale Avenue, London NW9 5HT, ††Public Health Laboratory,West Park Hospital, Horton Lane, Epsom,Surrey KT19 8PB Summary: A foodborne outbreak of salmonella infection at a private hospital in London in 1994 was found
to be associated with eating turkey sandwiches prepared by a food handler. One patient, nine staff, and a
foodhandler’s baby were confirmed to have Salmonella enterica serotype virchow, phage type 26 infection. The
attack rate was estimated to be 5% among the approximately 200 patients and staff at risk. A food handler
reportedly became ill days after, but her baby days before, the first hospital case. Although it appeared to be a
single outbreak, antibiogram analysis, supplemented by plasmid profile typing, demonstrated that there were
two strains of S. virchow involved, one with resistance to sulphonamides and trimethoprim and a second sen-
sitive to these antimicrobial drugs. Mother and child had different strains. The investigation demonstrated the
importance of full phenotypic characterization of putative outbreak strains including antimicrobial suscepti-
bility testing.
Outbreaks of foodborne infection in hospitals are preventable and are associated with high attack rates and disruption of services. There is a need for good infection control policies and training of all staff involved inpatient care as well as in catering services. Consultants in Communicable Disease (CCDCs) should include pri-vate hospitals in their outbreak control plans. Good working relations between Infection Control Doctors (ICDs)in the private health sector and their local CCDCs are important if outbreaks are to be properly investigated.
Keywords: Food; Salmonella; hospital outbreak; handler. Introduction
(IID) in hospitals during 1992 to 1994.1 Outbreaksof IID in hospitals accounted for 14% (189/1273) Outbreaks of Salmonella infection in hospitals are of all IID outbreaks reported in the same period not very common constituting 12% (22/189) of the to the Public Health Laboratory Service (PHLS) reported outbreaks of infectious intestinal disease Communicable Disease Surveillance Centre(CDSC). Twelve of the 22 were described as spreadfrom person to person, eight as foodborne; and two Received 27 January 1999; revised manuscript accepted were in private hospitals. The outbreak reported here occurred in 1994, when in England and Wales Author for correspondence: B Walsh, Dept of Public Health (E&W), there were 30,428 laboratory reports to Medicine, Kingston & Richmond Health Authority, the PHLS CDSC of faecal isolates of salmonella 22 Hollyfield Road, Surbiton KT5 9AL.
organisms (excluding Salmonella enterica serotypes A retrospective cohort study was performed typhi and paratyphi) of which 2727 (9%) were involving catering and operating theatre staff, virchow.2,3 In South Thames region in the same year working between 7 and 11 November inclusive.
there were 3945 reports of salmonellas and 296 Structured questionnaires were distributed to these (7.5%) were S. virchow. Phage type 26 accounted for cohorts (N:80), with a covering letter from the 44% of isolates of S. virchow in E&W in 1994.
hospital Chief Executive. Cases included were those On 15 November 1994, it was reported to the with onset of any gastrointestinal symptoms (diar- Infection Control Doctor (ICD) that in a private rhoea with two or more loose stools in 24 h) between hospital in South London Salmonella spp. had been 7 and 18 November inclusive plus positive stool cul- cultured from the stool of a female patient aged 39.
ture for S. virchow phage type (PT) 26. Active sur- She had developed diarrhoea on 11 November veillance for cases of diarrhoea was carried out daily four days after undergoing a gynaecological opera- tion. On 16 November, the ICD was informed of Stool specimens for culture were obtained from some staff members ill with diarrhoea, and that all catering staff, and from any other staff with Salmonella spp. had been isolated from the stools gastro-intestinal symptoms and were submitted to of a food handler whose child was diagnosed with Epsom Public Health Laboratory. Microbiological salmonella infection several days previously. This investigation included bacterial, parasite and viral food handler apparently had some symptoms on examinations. All isolations from the putative out- 15 November. The Consultant in Communicable break were sent to the PHLS Laboratory of Enteric Disease Control (CCDC) was contacted by the Pathogens (LEP) for identification and typing.
hospital ICD and an Outbreak Control Team Methods used included serotyping,4 phage typing5 and plasmid profile typing.6 Strains were also tested for susceptibility to ampicillin, chloramphenicol, gen- S. virchow infection were reported (including the tamicin, kanamycin, streptomycin, sulphonamides, index case, two operating theatre staff members, tetracycline, trimethoprim, nalidixic acid and cipro- and one other staff member) all of whom had floxacin, using a breakpoint method on Isosensitest apparently eaten sandwiches in the hospital but had agar.7 Strains resistant to antimicrobial drugs were no other obvious common exposures. Control mea- tested for the ability to transfer resistance, either sures included exclusions of staff with symptoms directly or by mobilization, to a nalidixic acid- and enhanced surveillance of gastro-intestinal dis- ease in staff and patients as it was considered likely KL12(:K12nalr).8 Resultant exconjugants were that this could herald a large outbreak.
tested for resistance to antibiotics and plasmidprofiles were compared with those of the drug-resis-tant donor strains. Environmental Health Officers Investigation
(EHOs) inspected the kitchen and interviewed food The private hospital consisted of three wards and 37 beds. The wards had mainly single rooms withen-suite facilities. Patients were mostly in hospital for elective day-case procedures and short-staysurgery with an approximate throughput of 100 A total of 35 samples were collected in the course of patients per week. Approximately 90 consultant the investigation. S. virchow PT 26 was confirmed surgeons and physicians admitted patients to the in a total of 11 individuals (one patient, one hospital and there were 23 full and part time cater- food handler, her daughter and eight other staff) ing staff and 70 other staff. All food was prepared in (Fig. 1). There were no food samples available for the main kitchen; there were also three ward pantries where light snacks were prepared. There Completed questionnaires were received from 69 was a small kitchen for staff use on another floor.
members of the cohort of catering and operating The epidemiological study began with the null staff members studied (86% response rate). The hypothesis that there was no association between the overall attack rate of S. virchow infection at the hos- consumption of sandwiches prepared in the hospital pital was estimated as 5% among the nearly 200 at between 7 and 11 November 1994 and the develop- risk (patients and staff who reportedly could have ment of S. virchow gastro-intestinal infection.
eaten sandwiches during the critical period).
Date of onset of other symptoms in non cases Salmonella virchow hospital outbreak London 1994. Sequence of events.
Nine individuals in the cohort had S. virchow One of the cases was a catering assistant who phage type 26 isolated from their stools, but only made the sandwiches. She had worked during the seven of these fulfilled the case definition. Two critical period from 7 to 11 November. The onset developed stomach cramps or pain on 11 and 13 date of her illness (reportedly 15 November) was November respectively, but had no diarrhoea and not accurately recalled and a stool specimen taken were therefore excluded from the analysis.
on 15 November yielded S. virchow PT 26 fully Single variable analysis of explanatory variables in Salmonella virchow hospital outbreak London 1994 *, Fisher’s exact test was used to determine significance;, undefinedRR, Relative Risk sensitive to antimicrobial agents. Her two-year-old amongst the cases, and it must be considered that daughter had onset of a diarrhoeal illness and a stool this incident was not a single outbreak.
sample taken on 5 November. S. virchow PT 26 PT 26 was the most common S. virchow phage resistant to sulphonamides and trimethoprim type in humans in England and Wales in 1994 and (R-type SuTm) was isolated from the stool sample.
was also identified in strains from poultry. During Six of the 11 isolations, including that from the this period the majority of strains were drug- child, were of R-type SuTm; the remaining isola- sensitive but strains of R-type SuTm were also tions were drug-sensitive including that from the identified. In such strains resistance to sulpho- mother (catering assistant). All of the six isolations namides and trimethoprim was encoded by a plas- of R-type SuTm were characterized by possession of a plasmid of approximately 4.6 megadaltons S. virchow PT 26 and there was no significant loss (MDa). This plasmid, which coded for resistance to either on storage or on extended growth in culture sulphonamides and trimethoprim, was non-trans- medium (E. J. Threlfall, unpublished observations).
ferrable but could be readily mobilized to the recip- The strain of S. virchow PT 26 of R-type SuTm ient strain of E. coli K12 nalr.
isolated from the child of the catering assistant on 5 Table I shows the significant results from the November 1994 may have been the strain responsi- single variable analysis. The risk of illness was ble for infections in five cases (including the affected increased 13-fold for eating turkey sandwiches, and patient) from whom strains of this R-type were 6-fold for bacon sandwiches. Consumption of any subsequently isolated. In contrast the strain from sandwich and eating them on 10 November was the catering assistant, who apparently developed associated with increased risk of illness.
symptoms some 10 days after her daughter, was There were no major faults in kitchen structure, drug-sensitive. This suggests that a second, drug- practices or procedures in food hygiene. Previous sensitive strain of S. virchow PT 26 was almost inspections of the kitchens by the ICD and EHOs simultaneously responsible for infections in a fur- were passed as entirely satisfactory. On this occasion the following were noted: turkey breasts were cooked Both S. virchow PT 26 of R-type SuTm and as 12–17 lb joints and temperature probes were not S. virchow PT 26 sensitive to antimicrobial drugs working in the period 7–11 November. Investigation have been isolated from poultry (E. J. Threlfall, also revealed that the preparation sink in the kitchen unpublished observations), and in 1994 S. virchow was small and situated close to the salad preparation was the third most common serotype in domestic area. The sandwich refrigerator temperature was fowl.9 Furthermore, in 1994 S. virchow PT 26 infec- tion amongst humans in England and Wales wereoften associated with the consumption of chickensin restaurants or the home environment.10 The epi- Discussion
demiological information suggested that turkey The epidemic curve in this outbreak strongly sug- sandwiches prepared by the catering assistant were gested a point source. In light of co-incident infec- responsible for the two almost simultaneous out- tion in the child of a food handler it was felt likely breaks in this hospital. However in the absence of these were linked and the food handler had possibly direct microbiological evidence it cannot be contaminated sandwiches during preparation. But assumed that poor personal hygiene by the food there were two antimicrobial resistance patterns handler was responsible for the transmission of the two organisms to the patient and staff members. It guidance for control of infection in hospitals recom- is possible that this may have contributed to trans- mends that health authorities ensure private hospi- mission of the strain infecting the child, but equally tals and nursing homes pay particular attention to that could be a chance finding. The findings that their infection control arrangements.21 The arrange- temperature probes were not working in the critical ments are determined by the type of service pro- period following the cooking of turkey breasts, and vided by the institution regardless of whether it is in that the sandwich refrigerator was also not func- tioning correctly, strongly implies that poor prac-tices in the hospital kitchen were important factors Acknowledgments
in these outbreaks. Contaminated raw poultry mayhave harboured more than one salmonella strain.
We would like to thank the following who assisted in The investigation demonstrates the importance of the investigation of the outbreak: Dr J. Bendig, full phenotypic characterization of putative outbreak Consultant Microbiologist, Epsom Public Health strains including antimicrobial susceptibility testing.
Laboratory; Mrs L. R. Ward of the Laboratory of Without the results of the latter analyses especially, it Enteric Pathogens (LEP) Colindale for phage typing may have been assumed that a single strain was res- the strains associated with the outbreak; Mr R. Smart, ponsible for the two almost simultaneous outbreaks Borough Environmental Officer, Mr B. Gilbey, of S. virchow PT 26 infection in the hospital.
Deputy Borough Environmental Officer, and Ms Received wisdom is that food handlers are rarely C. Gilbert, Environmental Health Officer, Environ- the source of salmonella outbreaks. It is believed mental Health Department, Royal Borough of that provided they observe good personal and hand Kingston upon Thames; as well as Mrs G. Fenelon, hygiene, asymptomatic salmonella excretors are Public Health Department, Kingston and Richmond unlikely to transmit infection and this is reflected Health Authority and Ms M Hallegua, PHLS CDSC in current guidance.11,12 In a hospital outbreak of S. enteritidis PT 4 in London in 1995, person-to-person spread was thought to be responsible after References
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