Stainless Steel in Hygienic Applications

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© 2015 International Stainless Steel Forum

Contents1 Background

2 Active antimicrobial solutions

2.1 Overview

2.2 Silver-containing coatings

2.3 Copper and its alloys

2.3.1 Re-contamination

2.3.2 Biofilmformation

3 Whystatementsaboutantimicrobialeffectsshould be viewed with scepticism

4 Whystainlesssteelisapreferredoption

5 Conclusions

6 References

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1 BackgroundThere has been a discussion amongst experts andconsumersaboutantimicrobialpropertiesofmaterials. It has long been known that copper [1] and silver are metals which can inhibit the growth ofbacteria,virusesandfungi.Stainlesssteel,incontrast,isaninertmaterialand,althoughits easy cleanability makes it a proven solution wheneversanitizationisessential,itisnotinitselfbioactive.

Insomeapplications(e.g.touchsurfacesinhospitals),active,antimicrobialmaterialshavebeenproposedasasubstituteforstainlesssteels[2].Extensionsoftheideaintoprofessionalkitchens and handrails in public transport havealsobeendiscussed.Itisthepurposeofthispapertoputthediscussionaboutactive,antimicrobial materials into perspective. A summaryisprovidedofthereasonswhystainlesssteelisoftentheonlyviableoptionwhenthehighestlevelsofhygieneorsterilesurfacesarerequired.

Active antimicrobial surfaces vs. standard stainless steels: Summary of arguments

Comparisons between countries show that the occurrenceofhealthcare-relatedinfectionswith multiple-resistant micro-organisms is determinedbyfactorsotherthanmaterialselectionintouchsurfaces.Active antimicrobial surfaces in general

� arenoteffectiveagainstallmicro-organisms. There are many pathogenic micro-organismsandsomeofthemarelesssensitivethanotherstoactivesurfaces.Onlypropercleaninganddisinfectioncanremoveall relevant germs

� areoftenoverestimatedintermsofantibacterialefficiencybecausesomecurrent assessment methods are unable to identifydormantcells

Silver-containing coatings in particular � wearoffeasily � provide no visible indicators to show when

theantimicrobialeffectstartstofail � are expensive

Copper and its alloys � owetheirantibacterialeffecttotherelease

ofmetalions;however,thereareindicationsofdetrimentaleffectsofcopperontheenvironment

� have become associated with resistance

forminginbacteriasuchasE.coli � maybesofterandlesswear-resistantthan

stainless steel � are expensive

Stainless steel � hasalonghistoryofsuccessfuluseinthe

most demanding medical applications such asimplantsandsurgicalinstruments,whichrequire sterile conditions

� doesnotimplytheriskofmicro-organismsformingnewtypesofresistance

� doesnotundergochangesovertime;theefficiencyofcleaninganddisinfectionremains the same over many years

� hasahardersurfacethanmanyothermetallicalloysandmakesfixtureslesssusceptibletosuperficialdamagesuchasscratchesanddents,inwhichbiomassmayaccumulate

� is resistant to both corrosion and high temperatures. It can be sterilized by thermal process and (liquid or gaseous) chemicalagentswithoutcorrodingorlossofmechanical or physical properties

� ispassivesothereisvirtuallynoexchangeofions with the environment

� isacost-effectivehigh-performancematerial

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2 Active antimicrobial solutions

2.1 Overview

Certainmetalshaveanoligodynamiceffect:theyreleaseionsintotheenvironment,whichdamagethe cell walls and cell membrane. Some research also suggests that the DNA is damaged and preventedfromreplicating[3].

Whilebacteriaareaffectedbytheoligodynamiceffect,virusesaregenerallymuchlesssensitiveto it.

Forhygienicpurposes,silverandcopperareused.Theireffectshavebeenknownforcenturies–longbeforemicro-organismswereevendiscovered.Thedownsideisthattheirsurfacesoxidise,ifunprotected,requiringlabour-intensiveregularpolishing. This is why silver in cutlery and brass in hardware were to a large extent replaced by stainless steel when this material became commonly available in the early 20th century.

Recently,theuseoftheoligodynamiceffectofsilver and copper has been re-considered in hygiene-criticalapplications:

� IntheUnitedStates,silver-containingcoatingswere developed into an industrial solution [4]. They can be applied to metallic and other surfaces–amongthemtostainlesssteel.Theyareusedin,forinstance,ventilationductsandrefrigerators.

� The copper industry has launched an “Antimicrobial Copper” campaign [5]. It maintains that copper and its alloys (such as bronze,brass,cupronickelandcopper-nickel-zincalloys)canbeasolutiontooneofthemostseriousproblemsinthemedicalsector:hospital(or,moregenerally,healthcare)acquired(nosocomial)infections.Certainbacteria have become resistant to the usual antibiotics.Thebest-knowngermofthistypeis the methicillin-resistant staphylococcus aureus (MRSA). Experts hold the view that infectionscausedby“superbugs”(e.g.MRSA) in hospitals cost more lives than road accidents.

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Summary: silver-containing coatings

� are expensive � wearoffeasily � shownovisibleindicatorwhentheireffect

fades

2.2 Silver-containing coatings

Silver-containing coatings have been applied to various materials. These include a silver/zinc-containingzeolitematrix,whichisappliedtostainless steel and other materials. It is reported toreducecoloniesofmicrobesby85.5–99.9%after4hoursandvirtually100%after24hours.Applicationscanbefoundinventilationsystems,where the coating contributes to reducing the proliferationofgermsandfungi[6].

However,forsuchcoatingstobeefficient,arelativelyhighconcentrationof39–78µg/mlofsilverionsinthezeoliteisrequired[6]. Nevertheless,suchcoatingscanwearoffespeciallyifthecoatingisappliedwet,i.e.by spray painting. Powder coating produces somewhat more durable layers.

Worn and damaged coatings have a negative effectonthesurfacetopographyofthematerial.Theycanformcracksandcrevices,whichmakeitmorepronetotheadhesionandretentionoforganic matter. They have obvious limitations on surfaceswhichareexposedtowearandtear[7]. Overtime,thesilverisdepleted.Thesilverionrelease may also be inhibited in environments that contain sulphur and chloride ions [6]. Against the backgroundofvolatilesilverprices,thetreatmentcan be expensive.

2.3 Copper and its alloys

Copperisknowntohaveantimicrobialeffects.Copper ions can penetrate cell walls and obstructs cell metabolism [8]. Studies show that thecolonizationoftouchsurfacesinhospitalscanbereducedifcopperorcoppercontainingalloysareusedfortouchplates,lightswitches,doorhandles,watertapsandothers.Insomeofthesestudiesevenalimitedpresenceofcopper-containing materials in the environment isreportedtoreducethenumberofhospital-acquiredinfectionsstrongly[9].

However,theseresultsneedtobeinterpretedcarefully.Directcontactwiththepatientorcommonmaterialssuchastextiles,plastics,chinawareorglassshouldbemorerelevantforthetransferofmicro-organismsthanfixturesandfittings.Artefactsinanexperimentalsettingcouldexplainwhysometimessurprisinglystrongeffectsareshown:whenmedicalandcleaningstaffbecome aware that they are in an experimental situation,theymayobservethecleaninganddisinfectionregimesmorestrictlythanintheirnormal day-to-day work. The reported reduction innosocomialinfectionsmaythereforepartlybe attributable to variables that are related to humanbehaviourratherthanthesurfacecontactmaterial.

Thesurfacetopographyofmaterialshasastronginfluenceontheircleanability.Hardsurfacesare

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Summary:

� Releaseofcopperionscanmakepathogenic micro-organisms resistant to copper.

� Thetoxicorevenlethaleffectoncertaincells is not limited to pathogen germs butcanalsoaffectotherusefulmicro-organisms.

less susceptible to scratches and dents which canformmicroscopicrecessesinwhichdepositsmayaccumulateandbecomedifficulttowipeaway. Stainless steel grade 1.4301 (304) has a typicalhardnessof88(RockwellB-scale),whiletheequivalentvalueis10forcold-rolledcopper(1/8hard),42forCommercialBronze(1/4hard)andbetween55and65forvarioustypesofbrass[10].Incontactwithwater,coppercanreleaseions.Theanti-bacterialefficiencyofcopperdependsonthepresenceofhumidity.Biofilmsthatnaturallyoccuronfrequentlytouchedsurfacescan,however,actasabarrierbetweenthe copper and the micro-organisms and strongly reduce ion migration. There are indications that coppersurfaces,despiteregularcleaning,haveatendencytobuilduplayersofbiomassthatreducethereleaseofcopperionssignificantlyovertime[11].

Itshouldalsobeborneinmindthattheeffectofcoppercanbedetrimental.Long-termlow-level exposure to copper ions can lead to micro-organismsbecomingresistanttocopper,ashasbeenshowninthecaseofE.coli[12],[13],enterococci and Salmonella [13],[14]. It has been cited [14]thatsincethemid-1980s,copper-resistant bacterial pathogens have been detected repeatedly. As the antibiotic and heavy metal resistance genes are located on the same mobile geneticelements,itispossiblethatthenaturalselection pressure imposed by heavy metals indirectlyco-selectforantibioticresistance[15].

Inapplicationsoutsideofthemedicalsector,copperreleaseisoftenunwantedbecauseofitsenvironmentaleffectsasaheavymetal[16]. The releaseofcopperfromroofsisacaseinpoint.Thereleaserateofcopperhasbeenfoundtobebetween 1.3 and 2.0 g/m² per year [17],[18]:

� IntheNetherlands,theuseofcopperinroofsandrainwatersystemscanlocallyberestricted or measures can become necessary to reduce copper emissions. The maximum admissiblerisklevelforcopperinsurfacewateris3.8µg/landnewinstallationsmustnotaddmorethan10%ofthisleveltothepre-existing charge [19].

� InSweden,theenvironmentalprogrammeofthecityofStockholmfor2012–2015saysthat(PVCand)copperpipingshouldbeavoidedifsuitablealternativesareavailable.Inroofsandfacades,copper,zincandtheiralloysshouldbeavoidedunlessrunoff-wateristreated[20].

Therefore,therearegoodreasonstoquestionsolutionsthatworkbydeliberatereleaseofcopperionsintotheenvironment–alsoinahealthcare environment.

In addition to the question whether or not the human body and the environment should beexposedtohighconcentrationsofmetalions,therearealsofactorswhichmaylimitthepracticalusefulnessofcopperinhospitalenvironments.

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Summary:

Evenifbacteriadieawaywithintwohoursonacoppersurface,manyhandswilltypicallytouchthatsurfacewithinthesametimeframeand recontaminate it with germs.

Summary:

� Micro-organisms may not be killed quicklyenoughtocopewithlevelsofre-contamination experienced in a busy hospital environment.

� Inpractice,biofilmsaccumulateandreducetheeffectofcopperreleasestrongly.

� Copper and its alloys become progressively moredifficulttocleanovertime,whilethecleanabilityofstainlesssteelremainsthesamethroughoutitslife.

2.3.1 Re-contamination

The data suggest that visual assessment is a poorindicatorofcleaningefficacyinhospitalenvironments [21]. While cleaning methods can effectivelyremovepathogensfromsurfaces,studieshaveshownthatmorethanhalfofthesurfacesarenotadequatelycleanedandmaybecome re-contaminated within minutes. In several comparative studies copper seems to performparticularlywellbecauseitiscomparedwithmaterialssuchasplastics,woodorcomposites which tend to have rough and porous surfaces[22].

2.3.2 Biofilm formation

Ithasbeenknownthatbiofilmscancolonisealmostanysurface,includingglass,steel,cellulose and silicone which are the main materials used to produce medical devices. Some ofthelatestresultsshowthattheantimicrobialactivityofcopperdependsonaveryclosecontactbetweenthebacteriaandthecopper,thepresenceofhumidityandahighconcentrationofreleasedcopperionsintothesurroundingmedium.Thepresenceoforganicmatterinthesolutionalsoaffectstheantibacterialefficiencyofcopper [7],[23].

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3 Why statements about antimicrobial effects should be viewed with scepticism

Anoften-neglecteddifferentiationofvarious“antimicrobial”effectsisthedistinctionbetween

� thekillingofmicro-organisms,asdefined,forinstance,inEN14885[24];

� theirreduction;or � theinhibitionoftheirgrowth(bacteriostatic

effect),asdescribedintheJapanesestandardJISZ2801:2000,whichismostcommonlyreferredto[25].

Ithasbeenshownthatantimicrobialeffectsmayvarystronglybetweendifferentstrainsofbacteria.Somemaybemoresensitivetocopper,otherstosilver.Alsodifferentdetectionmethodsmayleadtodivergingresults,withsomeofthemsystematically overestimating antimicrobial efficiency[26].

Based on data by the European Antimicrobial ResistanceSurveillanceSystem(EARSS),thereisstrongvariabilityintherateofnosocomialinfectionsbetweencountries.Theprevalence(theoccurrenceinthetotalhospitalpopulation)ofinfectionswithMRSAissaidtobeabout1%intheNetherlands,DenmarkandotherScandinaviancountriesanduptonearly50%inothers[27].

Therearenoindicationsofsignificantdifferencesin the material mix used in hospital equipment betweenthosecountries.Specifically,theNetherlands and Scandinavia are not known to usemorecopperalloysthantherestofEurope.Asaconsequence,itseemsthatmaterialselectionintouchsurfacesisnotadecisivefactor.Instead,thestrikingdifferencesinMRSAprevalenceareobviously related to hygiene management. In somecountries,

� risk patients newly accepted to hospital aresystematicallyscreenedforMRSAandother multiple resistant pathogens and kept in quarantine until they have been tested negative;

� whencasesofMRSAinfectionsoccur,entirehospitalwardsmaytemporarilybeclosed;

� therehasbeenalonghistoryofpersistenthygiene measures and their strict implementation,oftenimplyingfull-timehygienists;

� sincethe1990s,apolicyofminimisingtheuseofantibioticsinthehealthcaresystemandinsociety as a whole has been pursued.

Againstthebackgroundofthesefindings,theuseofantimicrobialmaterialsintouchsurfacesappearstohaveonlyanegligiblepracticaleffect,

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Summary:

� “Antimicrobial” does not necessarily mean “killingmicro-organisms”–oftentheirgrowth is only inhibited.

� Inactivemicro-organismscansurvive,betransmittedandproliferateagainwhentheconditionsarefavourable.

� There are many dangerous micro-organisms. The studies published in a promotional context usually include only afewofthem–typicallythoseforwhichamarkedeffectcaneasilybedemonstrated.Onlycompleteremovalofmicro-organismsandthebiofilmsharbouringthemensuresthenecessarylevelofsafety.

� Antimicrobialsurfacesarenotasubstituteforthoroughandeffectivecleaningprocedures.

� International comparison suggests that theprevalenceofnosocomialinfectionsis strongly dependent on hygiene management,irrespectiveofthematerialsusedfortouchsurfaces.

ifany,ontheprobabilityofnosocomialinfections.Patients,hospitalstaffandvisitorsshouldnotbetemptedtorelyon“self-sanitizing”propertiesofantimicrobialmaterials.Arationalapproachtomaterialselectioninhospitaltouchsurfacesshouldthereforebegovernedbycriteriasuchas

� asurfacetopographythatisfavourabletothorough cleaning and does not deteriorate overtime;

� wearresistance; � and,providedthehygienicperformanceis

comparable,alsolife-cyclecost.

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4 Why stainless steel is a preferred option

While stainless steel does not have an active antimicrobialeffect,itisthepredominantmaterialin medical and other hygiene-critical applications [28]foranumberofreasons:

� Stainlesssteeliseasytocleanandsanitize–evenafterdecadesofservice.Incontrast,theperformanceofcopper-containingalloysandsilver-containing coatings will change over time.

� Stainless steel is inert. It does not lead to resistance-forminginmicro-organisms.Activesurfaces,incontrast,releaselargeamountsofmetalionsintotheenvironment,theeffectsofwhicharenotfullyknown.

� Stainless steel can be sterilized in multiple ways(chemically,thermally).Forcopperandsilver containing coatings the reactive nature ofthesurfacelimitstheoptions.

5 ConclusionsGoodcleaninganddisinfectionpracticesarekeyfactorsforthepreventionofnosocomialinfections.Activesurfacescannotreplacepropersanitisation.Ifdisinfectionisperformedaccordingtothecommonlyacceptedstandards,activesurfacesprovideatbestonlyamarginalbenefit.Thedisadvantagesofactivesurfacestypicallyinclude:

� weakeningefficiencyovertime; � lower mechanical resistance against wear and

damage; � higher investment cost.

Knowingthattouch-surfacesaretoacertainextent“self-sanitizing”mayalsoinducepersonnelto believe that they can be more lenient in terms ofcleaningandhanddisinfection.

Ifallofthesefactorsaretakenintoaccount,stainlesssteelcontinuestobeapreferableoptionfortouchsurfacesinhospitalsandinthepublicsector,especiallyinoldagehomes,inschoolsand in public transport.

6 References

[1] http://en.wikipedia.org/wiki/Antimicrobial_properties_of_copper asof12-12-2011

[2] First hospital in France installs antimicrobial coppertouchsurfacestocombatHCAIs.Antimicrobial Copper. http://www.antimicrobialcopper.com/media/210388/pr818-french-hospital-installs-copper-surfaces-to-combat-hcais.pdfasof12-12-2011

[3] Oligodynamiceffect.Wikipedia.http://en.wikipedia.org/wiki/Oligodynamic_effect as of12-12-2011

[4] Sciessent. How it works. AgIon. http://www.agion-tech.com/asof12-12-2011

[5] International Copper Association. Antimicrobial Copper. http://www.antimicrobialcopper.comasof12-12-2011

[6] Cowan,M.M.,Abshire,K.Z.,Houk,S.L.,EvansS.N.Antimicrobialefficacyofasilver-zeolitematrixcoatingonstainlesssteel.Syracuse,NewYork:Carrier,2003

[7] Gebel,J.EinflussvonmetallischenOberflächenmaterialienaufdiemikrobielleBesiedlungsowiederEinflussvonReinigung

undDesinfektion.Bonn:InstitutfürHygieneundÖffentlicheGesundheit,RheinischeFriedrich-Wilhelms-Universität,2009

[8] Childs,D.Thesciencebehindantimicrobialcopper. Antimicrobial copper. www.antimicrobialcopper.com_uk_scientific_proof/how_it_worksasof4-11-2011

[9] Copper clinical trials. Copper Development Association. www.copperinfo.co.uk_antimicrobial_clinical-trial.pdfasof4-11-2011

[10] Zahner,L.,Architecturalmetals:aguidetotheselection,specificationandPerformance,NewYork:JohnWiley,1995,p.14-15

[11] Airey,P.,Verran,J.Potentialuseofcopperasahygienicsurface;problemsassociatedwithcumulativesoilingandcleaning.JournalofHospitalInfection.2007,Vol.67

[12] Cooksey,D.A.,Copperuptakeandresistanceinbacteria,MolecularMicrobiology(1993)7(1),pp.1-5

[13] Aarestrup,F.M.,Hasman,H.,Susceptibilityofdifferentbacterialspeciesisolatedfromfoodanimalstocoppersulphate,zinc

chloride and antimicrobial substances used fordisinfection,VeterinaryMicrobiology100(2004),83-89

[14] Williams,J.R.,Morgan,A.G.,Rouch,D.A.,Brown,N.L.,Lee,B.T.O.,Copper-resistantentericbacteriafromUnitedKingdomandAustralianpiggeries,AppliedandEnvironmentalMicrobiology,Aug.1993,p.2531-2537

[15] Amachawadi,R.G.,Shelton,N.W.,Shi,X.,Vinasco,J.,Dritz,S.S.,Tokach,M.D.,Nelssen,J.L.,Scott,H.M.,Nagaraja,T.G.,SelectionoffecalenterococciexhibitingtcrB-mediatedcopperresistanceinpigsfeddietssupplementedbycopper,AppliedandEnvironmentalMicrobiology,Aug.2011,p.5597-5603

[16] Hilleband,T.,Toussaint,D.,Böhm,E.,Fuchs,S.,Scherer,U.,Rudolphi,A.,Hoffmann,M.,EinträgevonKupfer,Zink,undBleiinGewässerundBöden.AnaysederEmissionspfadeundmöglicherEmissionsminderungsmaßnahmen,Dessau:Umweltbundesamt2005(Texte,19/05)

ISSF STAINLESS STEEL FOR HYGIENIC APPLICATIONS - 11

[17]OdnevallWallinder,I.,Verbiest,P.,He,W.,Leygraf,C.Effectsofexposuredirectionandinclinationontherunoffratesofzincandcopperroofs.CorrosionScience42(2000)

[18]Hullmann,H.(ed.).NatürlichoxidierendeMetalloberflächen.UmweltauswirkungenbeimEinsatzvonKupferundZinkinGebäudehüllen.Stuttgart:FraunhoferIRBVerlag.

[19]Laurissen,F.,Milieuaspectenvankoperendakenengevels.Nijmegen:CopperBenelux,2007

[20] Stockholmsmiljöprogram2012-2015,StockholmStad,undated

[21] Malik,R.E.,Cooper,R.A.,Griffith,C.J.,Useofaudittoolstoevaluatetheefficacyofcleaningsystemsinhospitals,AmericanJournalofInfectionControl(2003),p.181-187

[22] Moran,W.R.,Attaway,H.H.,Schmidt,M.G.,John,J.F.,Salgado,C.D.,Sepkowitz,K.A.,Cantey,R.J.,Steed,L.L.,Michels,H.T.,Riskmitigationofhospitalacquiredinfectionsthroughtheuseofantimicrobialcoppersurfaces,PosterpresentedattheAmerican Hospital Association and Health

ForumLeadershipSummit2011,July17-19,2011,SanDiego,CA.http://www.antimicrobialcopper.com/media/149621/aha-health-forum-copper-reduces-infection-risk-2011.pdfasof2-2-2012

[23] Robine,E.,Boulangé-Peterman,L.,Derangère,D.,Assessingbacterialpropertiesofmaterials:thecaseofmetallicsurfacesincontactwithair,JournalofMicrobiologicalMethods49(2002),p.225-234

[24] EN14885:2007:Chemicaldisinfectantsandantiseptics–ApplicationofEuropeanStandardsofchemicaldisinfectantsandantiseptics.2007

[25] JISZ2801:2000Antimicrobialproducts–Testforantimicrobialactivityandefficacy

[26] Allion,A.,VanHecke,B.,Boubetra,A.,Lenestour,F.Methodologicalapproachofantibacterialsurfacescharacterization.ProceedingsoftheSeventhEuropeanStainlessSteelConferenceScienceandMarket,Como,Italy,21-23September2011.Rome:AssociazioneItalianadiMetallurgia,

2011

[27]AntimikrobielleKupferlegierungen-NeueLösungenfürGesundheitundHygiene,Düsseldorf:DeutschesKupfer-Institut,2nd edition 2010

[28]Heubner,U.,Stainlesssteel-Whenhealthcomesfirst.Brussels:EuroInox,2009.(EnvironmentandHumanHealthSeries,Volume 2)

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About ISSFThe International Stainless Steel Forum (ISSF) is a non-profitresearchanddevelopmentorganisationwhichwasfoundedin1996andwhichservesasthefocalpointfortheinternationalstainlesssteelindustry.

Who are the members?ISSFhastwocategoriesofmembership:companymembersandaffiliatedmembers.Companymembersareproducersofstainlesssteel(integratedmillsandrerollers).Affiliatedmembers are national or regional stainless steel industry associations. ISSF now has 65 members in25countries.Collectivelytheyproduce80%ofall stainless steel.

VisionStainlesssteelprovidessustainablesolutionsforeverydaylife.

More informationFormoreinformationaboutISSF,pleaseconsultour website worldstainless.org.

Formoreinformationaboutstainlesssteelandsustainability,pleaseconsultthesustainablestainless.org website.

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AcknowledgementThe present brochure is adapted from “Inertvs. antimicrobial – A position paper concerningstainless steel and competing materials in hygiene-criticalapplications”,unpublishedpaper,EuroInox2013.

DisclaimerTheInternationalStainlessSteelForumbelievesthattheinformationpresentedistechnicallycorrect.However,ISSF,itsmembers,staffandconsultantsspecificallydisclaimanyandallliabilityorresponsi-bilityofanykindforloss,damage,orinjuryresultingfromtheuseoftheinformationcontainedinthisbrochure.

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