Outbreak of Shiga toxin-producing Escherichia coli O157 linked with consumption of a fast-food product containing imported cucumbers, United Kingdom, August 2020
Ranya Mulchandani
a,b,*, Clare Brehmer
a, Saira Butt
c,h, Bhavita Vishram
c, Melissa Harrison
a, Elizabeth Marchant
b,e, Simon Ferris
f, Frieda Jorgensen
a, Robert Smith
g, Gauri Godbole
c, Claire Jenkins
c,h, Timothy J. Dallman
c,h,
Neville Q. Verlander
d, Nick Phin
c, Dan Todkill
a,i, Saheer Gharbia
c, Jeremy Hawker
a,haFieldService,PublicHealthEngland,Birmingham,UK
bUKFieldEpidemiologyTrainingProgramme,PublicHealthEngland,London,UK
cTuberculosis,AcuteRespiratory,Gastrointestinal,Emerging/ZoonoticInfectionsandTravelMigrantHealthDivision(TARGET),PublicHealthEngland,London, UK
dStatisticsUnit,PublicHealthEngland,London,UK
eSouthEastRegion,PublicHealthEngland,Oxford,UK
fEastMidlandsHealthProtectionTeam,PublicHealthEngland,Nottingham,UK
gCommunicableDiseaseSurveillanceCentre,PublicHealthWales,Cardiff,UK
hHealthProtectionResearchUnitinGastrointestinalInfections,UniversityofLiverpool,Liverpool,UK
iCommunicableDiseaseControlEvidenceandEpidemiology,WarwickMedicalSchool,TheUniversityofWarwick,Coventry,UK
ARTICLE INFO Articlehistory:
Received1March2021
Receivedinrevisedform1April2021 Accepted3April2021
ABSTRACT
Background:In August2020, anoutbreakof Shigatoxin-producingEscherichia coli(STEC) O157:H7 occurredin the UnitedKingdom. Whole genome sequencing revealed that these cases formed a geneticallydistinctcluster.
Methods:Hypothesesgeneratedfromcaseinterviews weretestedinanalyticalstudies,and results informed environmental sampling and food chain analysis.A case–case study used non-outbreak
‘comparison’STECcases;acase–controlstudyusedamarketresearchpaneltorecruitcontrols.
Results:Atotalof36caseswereidentified;allcasesreportedsymptomonsetbetweenAugust3and August16,2020.Themajorityofcases(83%)residedintheMidlandsregionofEnglandandinWales.A highproportionofcasesreportedeatingout,withonefast-foodrestaurantchainmentionedby64%(n= 23)ofcases.Boththecase–casestudy(adjustedoddsratio(aOR)31.8,95%confidenceinterval(CI)1.6–
624.9)andthecase–controlstudy(aOR9.19,95%CI1.0–82.8)revealedstatisticallysignificantresults, showing thatthe consumptionof a specific fast-food productwas independently associated with infection.
Conclusions:Consumptionofaspecificfast-foodproductwasalikelycauseofthisoutbreak.Theonly ingredientspecifictotheproductwascucumbers.Thesupplyofcucumberswasimmediatelyhalted,and nofurthercaseshavebeenidentified.
©2021TheAuthor(s).PublishedbyElsevierLtdonbehalfofInternationalSocietyforInfectiousDiseases.
ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc- nd/4.0/).
Introduction
Shigatoxin-producingEscherichiacoli(STEC)O157:H7arefood- bornezoonoticbacteriathatcancausegastroenteritis.STECO157:
H7areofsignificantpublichealthconcernintheUnitedKingdom duetotheseverityofsymptoms(Bryneetal.,2015),whichrange frommildtobloodydiarrhoea,withhaemolyticuraemicsyndrome (HUS),alife-threateningconditionofthekidneys,occurringina smallproportionofcases(Laundersetal.,2016a).
TheprincipalreservoirforSTECO157:H7isdomesticruminants (Blanco et al.,2001), primarily cattle,sheep,and goats.Human infectionscanoccurthroughdirectexposuretoinfectedanimals andtheirenvironment,theconsumption ofcontaminated food/
*Corresponding author at: Field Service Midlands, 5 St Philip’s Place, Birmingham,B32PW,UK.
E-mailaddress:ranya.mulchandani@phe.gov.uk(R.Mulchandani).
https://doi.org/10.1016/j.ijid.2021.04.001
1201-9712/©2021TheAuthor(s).PublishedbyElsevierLtdonbehalfofInternationalSocietyforInfectiousDiseases.ThisisanopenaccessarticleundertheCCBY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).
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Pleasecitethisarticleas:R.Mulchandani,C.Brehmer,S.Buttetal.,OutbreakofShigatoxin-producingEscherichiacoliO157linkedwith consumptionofafast-foodproductcontainingimportedcucumbers,UnitedKingdom,August2020,IntJInfectDis,https://doi.org/10.1016/j.
ijid.2021.04.001
ContentslistsavailableatScienceDirect
International Journal of Infectious Diseases
j o u r n a l h o m ep a g e : w w w . e l s e v i e r . c o m / l o c a te / i j i d
water, or human-to-human transmission (Byrne et al., 2014).
PreviousoutbreaksofSTECO157:H7intheUnitedKingdomhave been found to be associated with the handling of raw leeks (Launders et al., 2016b) and the consumption of watercress (Jenkinsetal.,2015),mixedsaladleaves(Gobinetal.,2018),raw drinkingmilk(Treacyetal.,2019),andfrozenbeefburgers(Byrne etal.,2020),amongothers.
IntheUnitedKingdom,STECO157:H7isthemostcommonly reportedserogroup,withPT8themostcommonphagetype(PT).
STECarecharacterizedbythepresenceofoneorbothShigatoxin genes(stx):stx1(ofwhichtherearethreesubtypes,namely1a,1c, and1d)and/orstx2(ofwhichtherearesevensubtypes,stx2a–2g).
The presence of stx2,specifically stx2a, is more likely tocause severedisease(Laundersetal.,2016a,b;Brandaletal.,2015).Inthe UnitedKingdom,therearethreelineages(I,II,andI/II)ofSTEC O157andsevensub-lineages,Ia–c,IIa–c,andI/II(Dallmanetal., 2015a).
OnAugust15,2020,aclusteroffiveSTECO157PT8stx1+stx2 werenotifiedtoPublicHealthEngland(PHE),allwithareported dateofsymptomonset betweenAugust8andAugust10,2020.
Whole genome sequencing (WGS) revealed that these cases formed a genetically distinct cluster. An incident management teammeetingwasheldonAugust18tocoordinatetheincident andguideappropriateepidemiological,microbiological,andfood chaininvestigations(Figure1).
Methods
Epidemiologicalmethods Casedefinitions
AconfirmedoutbreakcasewasamicrobiologicalcaseofSTEC O157:H7stx1a+stx2cwithaPHESingleNucleotidePolymorphism (SNP) type 2.154.2186.4115.5439.5892.% (t5.5892), who was residentintheUnitedKingdom.
Aprobable outbreakcasewasamicrobiologicalcaseofSTEC O157:H7,PT8,stx1+stx2,withadateofonsetorspecimendate fromAugust1,2020,awaitingWGS.
Enhancedsurveillanceandtrawlingquestionnaires
Standardizedenhancedsurveillancequestionnaires(ESQ)(PHE, 2019)wereadministeredtoallnewcaseindividualswithaSTEC infectionwithin24hofnotificationandreportedtotheNational EnhancedSurveillanceSystemforSTECinfection(NESSS)database heldbytheGastrointestinalPathogensUnit.AnalysisoftheESQs ledtothedesignofamoredetailedtrawlingquestionnaire(TQ)for confirmedcases,focusingonallfoodsconsumedbothinsideand outsideofthehome.
From August 21, 2020, the confirmed outbreak cases were contactedandaskedtocompleteaTQ.ThedatafromtheESQsand
TQswerecombinedtodescribefoodexposuresandtogenerate primaryhypothesesaboutpotentialvehiclesoftransmission.
Case–casestudy
Acase–casestudywasinitiatedonAugust26,2020totestthe initialhypothesesidentifiedthroughtheTQs(consumptionofone specificfast-foodproductfromrestaurantchainA,lettuceand/or cucumbers), utilizing NESSS data. Outbreak cases that were available in NESSS (which only includes cases from England) andthatmettheconfirmedcasedefinitionwerecomparedtonon- outbreak ‘comparison’ cases, which were (1) microbiologically confirmedcasesofSTECO157;(2)infectedwithadifferentPT(not PT8)orPT8withadifferentWGSprofileandnotassociatedwitha knownoutbreak;(3)withadateofonsetfromJuly1,2020;(4)no traveloutsidetheUnitedKingdomintheweekbeforesymptom onset;and(5)withanESQavailableinNESSS.Norestrictionswere placedonageorsex.
The data analysis was conducted in Stata 15. A univariate analysis was conducted to calculate the odds ratios (ORs) and corresponding95% confidence intervals(95% CIs). Any variable that was statisticallysignificant inthe univariateanalysis(Chi- squareP-value<0.05),hadanOR>3,wasaprimaryhypothesis,or wasconsideredapotentialconfounder(ageandsex)wasincluded ina multivariablemodel.Any variablethat hada WaldP-value
>0.05 was considered for removal; each variable was then removedindividuallyandalikelihoodratiotest(LRT)performed toexaminewhetheritimprovedthefitofthemodel(P<0.05).Any variablethat didnot improvethe fitof themodel was further consideredforremoval;iftheORforanyoftheremainingvariables changed by >20% on removal, it was considered a potential confounderandretained.Themultivariablemodelwasconsidered finalwhen nofurthervariablescouldberemoved.Firthlogistic regressionwasusedtocomputeadjustedORs(aORs)and95%CIsin the final multivariable model, due to zero exposures in the
‘comparison’group.
Case–controlstudy
Acase–controlstudywasinitiatedonSeptember23,2020to furthertestthetieredhypothesesofassociationwitheatingout, eatingatrestaurantchainA,consumptionoffast-foodproductX, and/orconsumptionofcucumber.Afoodexposurestudy-specific questionnaire was designed based upon these hypotheses.The sample size was calculated based onavailable data on lettuce consumption,assumingslightunderreporting(duetorecallbias):
45%incasesand15%incontrols.Assumingasignificancelevelof 0.05 andpowerof0.80, witha ratioof3:1controlstocases,a samplesizeof26casesand 78controlswas required.Inclusion criteria for controls were (1) age over 18 years; (2) had not experienceddiarrhoeaorvomiting,orbeeninclosecontactwith someonewitheithersymptom,andhadnottravelledoutsidethe UnitedKingdombetweenJuly27andAugust2,2020.
Controls wererecruited fromOctober 2 toOctober 6, 2020 throughamarketresearchpanel(Mooketal.,2018).Controlswere frequencymatchedbysex,age(>50years,<50years),andbroad geographic region (Midlands, Wales, and England excluding Midlands).Dataonexposuresforcontrolswerecollectedforthe periodAugust3toAugust9,2020;thistimeframewaschosento reflectasimilarexposureperiodtothecases.
ThedataanalysiswasconductedinStata15.Univariateanalysis wasconductedtocalculateORsand95%CIs.Anyvariablethatwas statisticallysignificant(Chi-squareP<0.05),hadanOR>3,orwas consideredapotentialconfounder(ageorsex)wasincludedinthe multivariable analysis, in a backwards, stepwise approach (full detailsunderthecase–casestudymethods).LRTwasalsousedto explore interactions of food exposures and geographic region.
LogisticregressionwasusedtocomputeaORsand95%CIs.
Figure1.Timelineoftheinvestigationandinterventions;Shigatoxin-producing EscherichiacoliO157:H7outbreak,UnitedKingdom,August2020.
Yellow: coordinationand managementof theoutbreak investigation;orange:
epidemiologicalinvestigations.Textingreen:microbiologicalinvestigations;text inred:controlmeasures.(IMT,incidentmanagementteam).
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Microbiologicalmethods Humansamples
IsolatesofE.coliO157fromcommunityandhospitalizedcases werereferredtotheGastrointestinalBacteriaReferenceUnitfor confirmationandtyping.Onreceipt,isolatesweretestedbyPCRto determinethepresenceof thegenesencoding Shigatoxin(stx1 and/or stx2), phage-typed, and sequenced on the Illumina sequencing platform, as described previously (Khakhria et al., 1990;Jenkinsetal.,2012;Dallmanetal.,2015b).Sequenceswere analysed todeterminethestxsubtype(Ashtonetal.,2015)and phylogeneticrelationshipbetweenisolatestoidentifythosethat fellwithinthesamefive-SNPsinglelinkagecluster,indicatingthat theisolateswerelikelytooriginatefromthesamesource(Dallman etal.,2018;Jenkinsetal.,2019).Sequencesweredepositedinthe National Center for Biotechnology Information Sequence Read ArchiveundertheBioProjectPRJNA315192.
The EnteroBase database (a publicly accessible database of genomes of several bacterial genera) was queried for isolates withina50-SNPoftheoutbreakstrain.Anurgentenquirywasalso posted onthe Epidemic Intelligence InformationSystem (EPIS) platformtodeterminewhetheranyothercountrieshaddetected relatedstrainsorwhetheranincreaseinSTECO157:H7stx1+stx2 hadbeendetectedinothercountries.
Foodsamples
Where available, samples of potential food sources/vehicles wereobtainedandtestedatthePHEFood,WaterandEnvironment (FW&E)laboratoryinLondon.TheFW&Elaboratorytestedallfood samples using PHE Standard Method F17 based on BS EN ISO 16654:2001DetectionofE.coliO157(ISO,2001).Thelaboratory usedbytheinternationalsuppliertestedalloftheirsamplesusing theISO16654:2001methodaswellastheinternationalstandard basedonISO/TS13136:2012(ISO,2012).
Foodchaininvestigations
The Food Standards Agency (FSA) co-ordinated food chain investigations with the establishments indicated by the initial epidemiologicalinvestigations,withaprimaryfocusonrestaurant chainA.AcommunicationwasraisedviatheRapidAlertSystem forFoodandFeed(RASFF)onAugust24toinformtheEuropean Unionoftheoutbreakinvestigation.
Results
Epidemiology
Descriptiveepidemiology
A totalof 36confirmedcases wereidentifiedaspartof this outbreak,withthedateofsymptomonsetrangingfromAugust3to August16,2020(Figure2).Twenty-fourcaseswerefemale(67%) and12weremale(33%).Caseswerebetween13and60yearsofage (median26years;interquartilerange19–32.5years).Caseswere distributed acrossEngland(n=27)andWales(n=9),withthe majority(58%)residinginthetwoMidlandsregions(n=21)(Figure 3).Clinicalinformationwasavailablefor33ofthecases:13were hospitalized and 25 reported bloody diarrhoea. There wereno reportsofHUS.
Enhancedsurveillanceandtrawlingquestionnaires
BetweenAugust23andAugust27,2020,TQswerecompleted with20confirmedcases.Ahighproportionofcaseshadconsumed foodfromrestaurantsand/or takeaways,withseveralreporting eatingoutmultipletimesinthe7dayspriortosymptomonset.The mostcommonestablishmentmentionedwasrestaurantchainA(n
=23,64%),with16reportingtheconsumptionoffast-foodproduct
X(70%).Ahighproportionalsoreportedeatingprocessedchicken products(n=27,75%),lettuce(n=23,64%),andcucumber(n=17, 47%). In total, 29 (81%) of theconfirmedcases reportedeating eithercucumber(insideoroutsidethehome)orthespecificfast- foodproductX(whichcontainedcucumber,chicken,lettuce,and sauce).Nocasesreportedeatinganothersimilarfast-foodproduct (product Y) available at the same restaurant chain, which contained a different chicken product, bacon, lettuce, tomato, andadifferentsauce,butnocucumber.
Case–caseanalysis
Atotalof27casesand80non-outbreakcase‘comparisons’were includedinthisanalysis.Fromtheunivariateanalysis,therewas evidence of an association between the consumption of raw vegetables,iceberglettuce,fast-foodproductX,Indiantakeaways andfoodfromseveralotherfoodestablishments,andtheoddsof infection.Inthemultivariableanalysis,therewasstrongevidence thattheconsumptionoffast-foodproductX (aOR31.79,95%CI 1.62–624.89),anIndiantakeaway(aOR6.99,95%1.16–42.30),and rawvegetables(aOR2.24,95%CI0.93–11.31)wereindependently associatedwithinfectionwiththeoutbreakstrain(Table1).
Case–controlanalysis
A total of 25 cases and 85 controls were included in this analysis.Theremaining11caseswerenotavailabletocompletethe studyquestionnaire.Singlevariableanalysiswasconductedtotest theaprioritieredhypotheses(Table2).Themultivariableanalysis indicated an association between outbreak cases and the consumptionoffast-foodproductX(OR 9.19,95% CI1.02–82.8;
P=0.048)(Table3).
Microbiology Humancases
Allisolatesfromthe36confirmedoutbreakcasesfellwithinthe samefive-SNPsinglelinkageclusterthatbelongedtolineageIIc.
STECO157:H7lineageIIcisgeographicallydispersedacrossEurope (Dallmanetal.,2021,accepted)andpreviousoutbreakshavebeen associatedwiththeconsumptionof vegetables(Launderset al., 2016b),salad(Sinclairetal.,2017),andherbs(Cowleyetal.,2016).
Certain clades are endemic in the United Kingdom cattle population (Food Standards Agency (FSA, 2018), while other cladesaremorecommonlyisolatesfromcasesreportingrecent traveltoother countriesin Europeand beyond (Figure 4).The phylogenetic placement of the outbreak strain indicated it belongedtoatravel-associated(i.e.,non-UnitedKingdom)clade.
Asnoneofthecaseslinkedtotheoutbreakreportedrecenttravel outsidetheUnitedKingdom,thisprovidedcircumstantialevidence thatthecontaminatedvehiclemayhavebeenimportedfood.The interrogation of EnteroBase identified the closest international Figure2. EpidemiccurveofconfirmedcasesofShigatoxin-producingEscherichia coliO157:H7duringtheoutbreak,UnitedKingdom,August2020(n=36).
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matchasasequencefromaDutchcattleisolatesampledin2007at a SNPdistance of 75 SNPs. Fifteencountries responded tothe urgentqueryonEPIS,withnonereportingrecentincreasesinSTEC O157:H7stx1+stx2oranyrelatedstrains.
Foodsampling
Elevensampleswereobtainedfromfast-foodoutletsandone retailerreportedbyacase(bothfromAugust18)andtested;these included shredded lettuce, cucumber, and breaded/pre-cooked chicken (including the ingredients of the implicated fast-food productXfromonerestaurantofrestaurantchainA).Additionally, loosesupermarketpeppersweretestedfromthehomeofonecase (onAugust24).AllofthesesamplestestednegativeforE.coliO157.
Foodchaininvestigations
TheFSAcontactedrestaurantchainAtorequestinformationon theirfoodsupplychain,foodproductionprocesses,andfoodsafety managementsystems.Therestaurantchainreportedthatbothraw materialsandfinishedproductunderwentregularmicrobiological testingandthatallproductwasnegative.Additionally,thisitem(as wellasseveralotheritems)hadonlybeenre-addedtothemenuin the weekprior tothe outbreak detection.The majorityof the implicatedrestaurantsfromrestaurantchainAweresuppliedbya singledistributioncentreintheMidlandsregion.Thecucumber suppliedtotheirrestaurantsviathisdistributioncentrewasgrown intheNetherlandsbyacorporationof11growersco-ordinatedby Figure3.GeographicspreadofoutbreakcasesbyresidentpostcodeinEnglandandWales;Shigatoxin-producingEscherichiacoliO157:H7outbreak,UnitedKingdom,August 2020.
Table1
Singlevariableandmultivariablemodelforthecase–casestudy;outbreakofShigatoxin-producingEscherichiacoli,UnitedKingdom,August2020.
Cases n(%)
Comparisonsn(%) OR(95%CI) aOR(95%CI) P-valuea
Fast-foodproductX 7(26%) 0(0%) 36.01(5.12–1) 31.8(1.62–625) 0.023
Indiantakeaways 7(26%) 4(5%) 6.65(1.77–24.98) 6.99(1.16–42.3) 0.034
Rawvegetablesb 15(56%) 20(25%) 3.75(1.51–9.34) 2.24(0.93–11.3) 0.066
Iceberglettuce 10(37%) 12(15%) 3.33(1.23–9.00) 2.35(0.65–8.58) 0.195
aOR,adjustedoddsratio;OR,oddsratio;CI,confidenceinterval.
aWaldP-valuesfrommultivariableanalysis.
bThiscomprisedawiderangeofdifferentvegetables,including(butnotexclusively)peppers,onions,broccoli,lettuce(unspecified),salad(unspecified),cucumber, cabbage.
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company G, and distributed to the United Kingdom through companyF,aswellasexportedtootherEuropeancountries(Figure 5). The implicated fast-food restaurant chain A immediately stoppedusingallthecucumbergrowersthathadbeenidentified onfirstnotificationoftheoutbreakandremovedallcucumbers fromrestaurantssuppliedbytheMidland’sdistributioncentre.
Discussion
Here,wedescribeanoutbreakofSTECO157thatoccurredinthe United Kingdom in August 2020. This study emphasizes how phylogenetic data were able to directly guide outbreak inves- tigations,throughcomparisonofexistingevidenceontheoutbreak sub-lineage and clade (sub-lineage IIc is more frequently associated with outbreaks from fresh produce, and with data available onEnteroBase wewere ableto linkthe strain tothe Netherlands).
Epidemiological investigations provided rapid and strong evidence that a vehicle of infection was a specific fast-food product(productX)fromarestaurantchain(restaurantchainA), and the most likely cause of the contamination was through importedcucumbers,providingfurtherevidencethatsaladitems areanimportantvehicleofSTECoutbreaks.Thisimplicatedfast- foodproducthadrecentlybeenre-addedtothemenu,asthechain had previously only offered a limited menu due to COVID-19 restrictions.Thesuspectedbatchofcucumberswasimmediately Table2
Singlevariableanalysisfocusingonapriorihypotheses:consumptionoffoodatrestaurantchainA,consumptionofproductX,and/orconsumptionofcucumber;outbreakof Shigatoxin-producingEscherichiacoli,UnitedKingdom,August2020.
Studypopulation Variable Cases
n/N(%)
Controlsn/N(%) OR(95%CI) P-value Allcases+controls
(n=110)
Atethefast-foodproductX 10/25(40%) 2/85(2%) 27.7(4.95–271) <0.001 Allcases+controls
(n=106)
Atethefast-foodproductX and/orcucumberseparately
23/25(92%) 28/81(36%) 21.8(4.69–198) <0.001 OnlythosethatateatrestaurantchainA(
n=28)
Atethefast-foodproductX 10/13(77%) 2/15(13%) 21.7(2.35–265) <0.001 Allcases+controls
(n=106)
Atecucumber 22/25(88%) 26/81(32%) 15.5(4.02–85.8) <0.001
Allcases+controls (n=110)
Ateout 23/25(92%) 42/85(49%) 11.8(2.59–107) <0.001
OnlythosethatdidnoteatatrestaurantchainA(
n=82)
Atecucumber 10/12(83%) 22/66(33%) 10.0(1.84–98.6) 0.001
Allcases+controls (n=110)
AteatrestaurantchainA 13/25(52%) 15/85(18%) 5.06(1.71–14.7) <0.001 Onlythosethathadeatenout
(n=65)
AteatrestaurantchainA 13/23(57%) 15/42(36%) 2.34(0.73–7.53) 0.105
OR,oddsratio;CI,confidenceinterval.
Table3
Singlevariableandfinalmultivariablemodelforthecase–controlstudy;outbreakofShigatoxin-producingEscherichiacoli,UnitedKingdom,August2020.
Cases n(%)
Controlsn(%) OR(95%CI) aOR(95%CI) P-valuea
Fast-foodproductX 10(40%) 2(2%) 27.7(4.95–271.21) 9.19(1.02–82.8) 0.048
Cucumberb 22(88%) 26(32%) 15.5(4.02–85.8) 5.84(0.24–141.03) 0.277
Readymealfromanysupermarket 7(28%) 5(6%) 6.22(1.47–27.34) 5.40(0.71–41.02) 0.103
Italianrestaurant 5(20%) 3(4%) 6.83(1.19–46.59) 4.98(0.18–21.77) 0.800
Eatingtomatooutsidethehome 12(48%) 7(9%) 9.76(2.84–34.38) 4.20(0.65–27.05) 0.131
Anylettuce 24(96%) 37(46%) 28.5(4.14–1199.47) 3.64(0.10–127.24) 0.477
Age Linearfunction 0.898(0.844–0.956) 0.001
Femalesex 15(64%) 46(54%) 1.51(0.55–4.31) 0.941(0.136–6.500) 0.951
aOR,adjustedoddsratio;OR,oddsratio;CI,confidenceinterval.
aWaldP-valuesfrommultivariableanalysis.
bConsumptioneitherinsideoroutsidethehome.
Figure4. MaximumlikelihoodphylogenyofCC11–lineageIIccomplexcolouredby travel(blue)oranimalorigin(green),fromtheoutbreakofShigatoxin-producing Escherichia coli,UnitedKingdom,August2020.Themonophyleticcladewhere outbreakstraint5:5892clustersishighlightedinpink.
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discardedonnotification oftheoutbreak totheretailerandno furthercaseswereidentified.Strongcommunicationlinkswiththe restaurantchain,EuropeanUnion(viaRASFF),andDutchauthori- tiesenabledtheswiftandin-depthanalysisoffoodchains.These timely interventionsledtoanimmediate reductionin risk and outbreakcontrol.Together,thisreporthighlightsthegoodpractice with respectto early detection of the outbreak based onlocal exceedances, combined with ESQs, which provided an early indicationthat eatingout atrestaurant chainAwas acommon exposureamongcases.
Onenoteworthyaspectof thisoutbreak isthatthecontami- natedvehiclewasfreshproduce,raisingmultiplechallenges.For instance, patientsoftenneglecttomentionsaladitemsintheir foodhistories.Thiswasobservedinthecase–controlstudy,where individuals who ate cucumber-containingitems did not report having eaten cucumber, and this may have led to an under- estimation or obscuring of further effects. Secondly, the short shelf-lifeoftheseitemsmeansthatthecontaminatedfooditems areoftennotavailablefortestingduringoutbreakinvestigations.
Inthisoutbreak,whileingredientsfromfast-foodproductXwere tested2dayspriortothecucumberbatchbeingdiscarded,noSTEC contaminationwas detected. However,such negativemicrobio- logical findings inimplicated foodproducts(especiallyinsalad products)arenotuncommon,asSTECcanbereportedlydifficultto isolatefromimplicatedfoodduetotheinfectiousdoseoftenbeing belowthatdetectedbystandardtesting(Byrneetal.,2016).For instance, in a United Kingdom-based outbreak linked to salad leaves, despite large numbers of salad leaves tested, the only samplespositivefortheoutbreakstraincamefromtheirrigation water(whichcouldbefilteredandthereforeconcentratedbefore testing)(Jenkinsetal.,2015).InanotherUnitedKingdom-based outbreak linkedtounpasteurizedmilk,theoutbreak strainwas onlysuccessfullydetectedincattlefaecalsamples(Treacyetal., 2019).Thisemphasizestheimportanceofproactivesamplingand surveysofcattle/sheeptoobtainmicrobiologicalconfirmationthat nearbyanimalreservoirsarecolonizedwiththeoutbreakstrain (Söderströmetal.,2008),andreinforcestheimportanceofrobust epidemiological and food-tracing evidence. Finally, despite the foodbusinessoperatorstestingforE.coli,itwasnotdetectedprior toorduringthisoutbreak,which questionsthemeaningfulness andutilityofpost-harvest/pre-supplytesting.Additionallyresist- ance tosharingadequate detailsofcomplexsupplychainsfrom food businessoperatorslimited andconfounded thetrace-back efforts.
Therewereseverallimitationstotheepidemiologicalstudies that are important to note. The case–case analysis used data previouslycollectedandheldinNESSSandassuch,someofthe variableswerenotidealforthepurposeofthisinvestigation:e.g.
‘rawvegetables’couldincludeanysaladorvegetableitemsandthis
madeitdifficulttoidentifycertainitemsofinterestortestwider consumption. As with all case–case analyses, the use of non- outbreak‘comparison’casesmayhaveresultedinover-matching ofexposureswithoutbreakcases,reducingourabilitytodetect risk factors for infection. However, the speed of thecase–case study(analysiswithinapproximately48hfollowingtheoutbreak report) enabled us totest theprimary hypothesesat pace and guided rapid public health action, which may not have been achievedthroughalternativestudydesigns.
Thedecisiontoproceedwithacase–controlstudyaddedtothe strengthofevidencebutattheexpenseoftime.Thisislikelyto haveledtorecallbiasinbothcases,whosefoodexposureswere6– 8weeksprior,andcontrols,whowereaskedaboutfoodexposures duringaparticularweek2monthspriorinordertocoverasimilar time period to cases and take account of the impact of a governmentschemeencouragingpeopletoeatoutduringAugust 2020.Additionally,theexposureperiodforcontrolswasrestricted toasingleweek–August3toAugust9–despitethesymptom onsetofcasesbeingoverAugust3toAugust16;thismayhaveled to some under-reporting if cases/controls had differing food exposuresintheperiod August9–16.Despitetheselimitations, thiscase–controlstudyisafurtherexampleofthesuccessinusing market researchpanel-generated controls, allowing for a rapid responseandrequiringlowresource,toaidrapidandcost-efficient resultstoguideoutbreakmanagement.
Ethicalapproval Notapplicable.
Conflictofinterest None.
Acknowledgements
Theauthorswouldliketothankallmembersoftheoutbreak controlteamfortheirvaluablecontributions.Theviewsexpressed arethoseoftheauthor(s)andnotnecessarilyoftheNHS,theNIHR, the Department of Health and Social Care, or Public Health England.
Transparencydeclaration
Thisarticleispublishedaspartofasupplementtitled,“Field Epidemiology:TheComplexScienceBehindBattlingAcuteHealth Threats,”whichwassupportedbyCooperativeAgreementnumber NU2HGH000044,managedbyTEPHINET(aprogramofTheTask ForceforGlobal Health)andfunded bytheCenters forDisease Control and Prevention (CDC). Its contents are solely the responsibility of the authors and do not necessarily represent theofficialviewsoftheCentersforDiseaseControlandPrevention, theDepartmentofHealthandHumanServices,TheTaskForcefor GlobalHealth,Inc.,orTEPHINET.
References
AshtonPM,PerryN,EllisR,PetrovskaL,WainJ,GrantKA,etal.InsightintoShiga toxingenesencodedbyEscherichiacoliO157fromwholegenomesequencing.
PeerJ2015;3:e739,doi:http://dx.doi.org/10.7717/peerj.739.
BlancoJ,BlancoM,BlancoJE,MoraA,AlonsoMP,GonzalezEA,etal.Epidemiologyof verocytotoxigenicEscherichiacoli(VTEC)inruminants.In:DuffyG,GarveyP, McDowellD,editors.VerocytotoxigenicEscherichiacoli.Food&NutritionPress, Inc;2001.p.113–48.
BrandalLT,WesterAL,LangeH,LøbersliI,Bjørn-ArneL,VoldL,etal.Shigatoxin- producingEscherichiacoliinfectionsinNorway,1992-2012:characterizationof isolatesandidentificationofriskfactorsforhaemolyticuremicsyndrome.BMC InfectDis2015;15:324,doi:http://dx.doi.org/10.1186/s12879-015-1017-6.
Figure5.Supplychainforcucumberusedinfast-foodproductXfromrestaurant chainA(thedashedlineindicatesanindirectsupplychain).
xxx–xxx
ByrneL,VanstoneGL,PerryNT,LaundersN,AdakGK,GodboleG,etal.Epidemiology andmicrobiologyofShigatoxin-producingEscherichiacoliotherthanserogroup O157inEngland,2009-2013.JMedMicrobiol2014;63:1181–8,doi:http://dx.
doi.org/10.1099/jmm.0.075895-0.
Bryne L, Jenkins C, LaundersN, Elson R, Adak GK, etal. Theepidemiology, microbiologyandclinicalimpactofShigatoxin-producingEscherchiacoliin England, 2009-2012. EpidemiolInfect 2015;3475–86, doi:http://dx.doi.org/
10.1017/s0950268815000746.
Byrne L, Adams N, Glen K, DallmanTJ, Kar-Purkayastha I, Beasley G, et al.
Epidemiological andmicrobiologicalinvestigationofanoutbreakofsevere diseasefromShigatoxin-producingEscherichiacoliO157infectionassociated withconsumptionofaslawgarnish.JFoodProt2016;79(7):1161–8,doi:http://
dx.doi.org/10.4315/0362-028X.JFP-15-580.
ByrneL,KaindamaL,BentleyM,JenkinsC,AirdH,OliverI,etal.Investigationintoa nationaloutbreakofSTECO157:H7associatedwithfrozenbeefburgers,UK, 2017. Epidemiol Infect 2020;148(July):e215, doi:http://dx.doi.org/10.1017/
S0950268820001582.
CowleyLA,DallmanTJ,FitzgeraldS,IrvineN,RooneyPJ,McAteerSP,etal.Short- termevolutionofShigatoxin-producingEscherichiacoliO157:H7betweentwo food-borneoutbreaks.MicrobGenomics2016;2(September(9))e000084,doi:
http://dx.doi.org/10.1099/mgen.0.000084.
DallmanTJ,ByrneL,AshtonPM,etal.Whole-genomesequencingfornational surveillance ofShigatoxin-producing Escherichiacoli O157.ClinInfectDis 2015a;61(August (3))305–12, doi:http://dx.doi.org/10.1093/cid/civ318 Epub 2015April17.
DallmanTJ,AshtonPM,BryneL,etal.Applyingphylogenomicstounderstandthe emergenceofShiga-toxinproducingEscherichiacoliO157:H7strainscausing severehumandiseaseintheUK.MicrobGenomics2015b;1(September(3)),doi:
http://dx.doi.org/10.1099/mgen.0.000029.
DallmanT,AshtonP,SchaferU,etal.SnapperDB:adatabasesolutionforroutine sequencinganalysisofbacterialisolates.Bioinformatics2018;34(September (17)):3028–9,doi:http://dx.doi.org/10.1093/bioinformatics/bty212.
DallmanTJ,GreigDR,GharbiaSE,JenkinsC.PhylogeneticstructureofShigatoxin- producingE.coliO157:H7fromsub-lineagetoSNPs.MicrobGenomics2021;, doi:http://dx.doi.org/10.1099/mgen.0.000551Onlineaheadofprint.
FoodStandardsAgency(FSA).E.coliO157super-sheddingincattleandmitigationof humanrisk.November.2018.https://www.foodstandards.gov.scot/downloads/
Super-shedders_-_FINAL_version_for_publication.pdf.
GobinM,HawkerJ,ClearyP,InnsT,GardinerD,MikhailA,etal.Nationaloutbreakof Shigatoxin-producingEscherichiacoliO157:H7linkedtomixedsaladleaves, UnitedKingdom,2016.Eurosurveillance2018;23(18):17–00197,doi:http://dx.
doi.org/10.2807/1560-7917.ES.2018.23.18.17-00197.
ISOstandard.Microbiologyoffoodandanimalfeedingstuffs–horizontalmethod forthedetectionofEscherichiacoliO157.Available:.2001.https://www.iso.org/
standard/29821.html.
ISOstandard.Microbiologyoffoodandanimalfeed–real-timepolymerasechain reaction(PCR)-based method forthe detection offood-borne pathogens– horizontalmethodforthedetectionofShigatoxin-producingEscherichiacoli
(STEC)andthedeterminationofO157,O111,O26,O103andO145serogroups.
Geneva:ISO;2012.
JenkinsC,LawsonAJ,CheastyT,WillshawGA.Assessmentofareal-timePCRforthe detectionand characterization ofverocytotoxigenic Escherichiacoli. JMed Microbiol 2012;61(August (Pt 8)):1082–5, doi:http://dx.doi.org/10.1099/
jmm.0.041517-0.
JenkinsC,DallmanTJ,LaundersN,WillisC,BryneL,JorgensenF,etal.Publichealth investigationoftwooutbreaksofShigatoxin-producingEscherichiacoliO157 associatedwithconsumptionofwatercress.ApplEnvironMicrobiol2015;81 (June(12)):3946–52,doi:http://dx.doi.org/10.1128/AEM.04188-14.
JenkinsC, DallmanTJ,GrantKA.Impactofwhole genomesequencingonthe investigationoffood-borneoutbreaksofShigatoxin-producingEscherichiacoli serogroupO157:H7,England,2013to2017.EuroSurveill2019;24(January(4)) 1800346,doi:http://dx.doi.org/10.2807/1560-7917.ES.2019.24.4.1800346.
KhakhriaR,DuckD,LiorH.Extendedphage-typingschemeforEscherichiacoliO157:
H7. Epidemiol Infect 1990;105:511–20, doi:http://dx.doi.org/10.1017/
s0950268800048135.
LaundersN,BryneL,JenkinsC,etal.DiseaseseverityofShigatoxin-producingE.coli O157andfactorsinfluencingthedevelopmentoftypicalhaemolyticuraemic syndrome:a retrospectivecohortstudy,2009–2012.BMJOpen 2016a;6(1) e009933,doi:http://dx.doi.org/10.1136/bmjopen-2015-009933.
LaundersN,LockingME,HansonM,etal.AlargeGreatBritain-wideoutbreakof STECO157phagetype8linkedtohandlingofrawleeksandpotatoes.Epidemiol Infect 2016b;144(January (1)):171–81, doi:http://dx.doi.org/10.1017/
S0950268815001016.
MookP,McCormickJ,KanagarajahH,AdakGK,ElsonR,GobinM,etal.Online market research panel members as controls in case-control studies to investigategastrointestinaldiseaseoutbreaks:earlyexperiencesandlessons learntfromtheUK.EpidemiolInfect2018;146(March(4)):458–64,doi:http://
dx.doi.org/10.1017/S0950268817002953.
PublicHealth England. Questionnaireforpatients with shigatoxin-producing Escherichiacoli(STEC),forreportingandsurveillance.Available:.2019.https://
www.gov.uk/government/publications/vero-cytotoxin-producing-escherichia- coli-questionnaire.
SinclairC,JenkinsC,WarburtonF,AdakGK,HarrisJP.Investigationofanational outbreakofSTECEscherichiacoliO157usingonlineconsumerpanelcontrol methods: Great Britain, October 2014. Epidemiol Infect 2017;145(April (5)):864–71,doi:http://dx.doi.org/10.1017/S0950268816003009.
SöderströmA,OsterbergP,LindqvistA,JonssonB,LindbergA,UlanderSB,etal.A largeEscherichiacoliO157outbreakinSwedenassociatedwithlocallyproduced lettuce.FoodbornePathogDis2008;5:339–49,doi:http://dx.doi.org/10.1089/
fpd.2007.0065.
TreacyJ,JenkinsC,ParanthamanK,JorgensenF,Mueller-DobliesD,AnjumM,etal.
OutbreakofShigatoxin-producing Escherichia coliO157:H7linkedto raw drinkingmilkresolvedbyrapidapplicationofadvancedpathogencharacteri- sationmethods,England,AugusttoOctober2017.Eurosurveillance2019;24 (April (16))1800191, doi:http://dx.doi.org/10.2807/1560-7917.
ES.2019.24.16.1800191.
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