Incidence and risk factors for microbial keratitis.docx

Incidence and risk factors for microbial keratitis.docx

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Incidenceandriskfactorsformicrobialkeratitis

ClinicalStudy

Eye（2002）16,608–618.doi:

10.1038/sj.eye.6700151

IncidenceandriskfactorsformicrobialkeratitisinHongKong:

comparisonwithEuropeandNorthAmerica

DSC Lam1,E Houang2,DSP Fan1,D Lyon2,D Seal3andE Wong4theHongKongMicrobialKeratitisStudyGroup

1DepartmentofOphthalmology&VisualSciencesPrinceofWalesandHongKongEyeHospitalsTheChineseUniversityofHongKong,HongKongPeople’sRepublicofChina

2DepartmentofMicrobiologyPrinceofWalesandHongKongEyeHospitalsTheChineseUniversityofHongKongHongKongPeople’sRepublicofChina

3AppliedVisionResearchCentreCityUniversityNorthamptonSquareLondonEC1V0HB,UK

4CenterforClinicalTrialsandEpidemiologicalResearchPrinceofWalesandHongKongEyeHospitalsTheChineseUniversityofHongKongHongKongPeople’sRepublicofChina

Correspondence:

ProfessorDSCLam,Tel:

（852）27623157Fax:

（852）21941369E-mail:

dennislam@cuhk.edu.hk

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Abstract

Purpose Toestablishtheincidence,etiologyandriskfactorsformicrobialkeratitis（MK）inHongKong.

Methods Twohundredandtwenty-threenewcasesofpresumedMKwererecruitedoveraperiodof17monthsandcomprehensivemicrobiologicstudiesperformed.Anestedcase-controlstudywaspursuedforpatientswearingcontactlenses（CLW）todetermineriskfactorsforMKwithregardstotypesofCLWandhygienepractice.

Results Ofthe223patientsrecruited,59（26%）worecontactlenses.Cornealscrapesyieldedpositiveculturesfrom77patients（35%overall,56non-CLW,21CLW）.TwohundredandsixCLWvolunteerswererecruitedtoparticipateinthecase-controlstudy,ofwhom135werematchedwith45CLWpatients.TheannualincidenceofMKwas0.63per10 000populationand3.4per10 000CLWwithratesfordaily,extendedandrigidlenswearof3.09,9.30and0.44per10 000CLWrespectively.Pseudomonasaeruginosawasthedominantbacterialpathogen.SixcasesofAcanthamoebakeratitisoccurred,fiveinCLW（incidence0.33per10 000CLW）andonefollowingcornealabrasion.Non-CLWdevelopedMKatapeakageof73,whichis10yearsyoungerthanexpectedforScotlandandUSA.

Conclusions PreviousocularsurfacediseaseandtraumawerethemainriskfactorsforMKinHongKong.CLWappearsatleastassafeasthatfoundinScotlandandtheUSA.AcanthamoebakeratitiswasdetectedbutwithanincidenceratefivetimeslowerthanScotland.FactorspredisposinghydrogelCLWstoMK,thatwerestatisticallysignificant,includedovernightwear,poorhygieneandsmoking.

Keywords:

microbialkeratitis;incidence;contactlens;riskfactors

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Introduction

Ulcerativeandnon-ulcerativekeratitisduetoinfectionisapotentiallyblindingconditionthatisgenerallyonlyfoundineyeswithapredisposingelement.Contactlens（CL）wearisrecognizedasanincreasinglycommonriskfactorinotherwisehealthyeyes.1,2,3WhennotassociatedwithCLuse,itmaybediagnosedinpatientsofallagegroupsandtraumamaybeapredisposingfactor.WiththegrowthoftheCLuserpopulationsincethe1980s,thisfactorhasincreasedastheprimarypredisposingcauseformicrobialkeratitis（MK）intheUSAbutnotforScotlandandEngland.2,3Riskfactorssuchasextendedwearofthelens,especiallysleepingwiththelensintheeye,havebeendescribed4,5buthaveneverbeeninvestigatedinasubtropicalFarEastclimate.

Microbialkeratitishasbeenreportedduetoinfectionwithawiderangeoforganisms.Thereareregionalvariationsinthepredominanceofdifferentmicrobes,reflectingdifferentpatientpopulationsandclimaticeffects.Fungiareimportantinthetropicalregions,suchasSouthIndiaandGhana.6,7AcanthamoebahasbeenidentifiedamongCLrelatedinfectionsinmanypartsoftheworld.8

ThereislittleinformationonMKand/orCL-relatedinfectionsinAsia,althoughthenumberofCLwearersisexpectedtoincreaserapidly,particularlyamongtheyoung.ThisisespeciallylikelyinChinawheretheprevalenceofmyopiaisonarisingtrend.MKcausedbyunusualpathogensrequiresspecificandoftenexpensivediagnosticmethodsandtherapies.Acost-effectiveapproachinthediagnosis,managementandpreventionofthisconditionisonlypossiblewhentheincidence,relativeimportanceofdifferentmicrobialagentsandpredisposingfactorsareknown.ThecauseofsuchinfectionhasneverbeenfullyinvestigatedinSouthChina,inparticularinthesemi-tropicalurbanclimateofHongKong.

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Materialsandmethods

AprospectivestudyofMKwasconductedbetweenApril1997andAugust1998withpatientsfromthetwohospitalswithEyeUnits—HongKongEyeHospital（HKEH）andthePrinceofWalesHospital（PWH）—servingourterritoryofKowloonandNewTerritoryEast,whopresentedwithsuchaclinicaldiagnosisandgaveoralconsent.MKwasdefinedastheclinicalpresentationof acornealstromalinfiltrate>1mm2usuallybutnotnecessarilywithanoverlyingepithelialdefect.Theonsetofpain,redness,blurredvision,foreignbodysensation,photophobia&dischargewereallrecordedaswasthevisualacuityonpresentation.Inaddition,thesizeoftheoverlyingdefectandthepositioninthecornea（axial,paraxialorperiphery）wererecorded.Typicalinflammatorykeratitissuchasmarginalkeratitis,andviralkeratitisduetoherpesandadenoviruseswereexcluded.Riskfactorssuchasoculartrauma,previousocularsurfacedisease（OSD）,contactlenswear（CLW）andhistory,applicationofsteroidorantibiotic（s）andhistoryofherpeticinfectionwererecordedonpresentation.Thecharacteristicsoftheulcer/infiltrate（sizeinsquaremm,shape,siteandanteriorchamberactivity）werenoted.

InordertoassesshowmanycasesofMK（excludingclassicalinflammatory,herpeticandadenovirusinfection）existedinHongKongprivatepractice,aquestionnairewassenttoallthe27privateophthalmologistsinourareaontwooccasionsduringthestudyperiod.Theywereaskedtoestimatethenumberofcasestheyhadseenandthenumbertheyhadreferredtothetwostudycentersintheprevious3months.AllHongKongophthalmologistsandtheHongKongOptometricAssociationwereinformedofthisstudyandaskedtohelpreferpatientswithMKthatcouldbeconsideredduetobacteria,fungioramoebaetooneofthetwohospitalsmentionedaboveforinvestigationandtreatment.

Usingpreservative-freeamethocaineeyedropsforlocalanesthesia,cornealscrapingswereperformedinallcaseswithaKimuraspatula.MicroscopywasperformedonGram-stainedsmearsofthecornealsample.Inoculationofbloodandchocolateagarsandthioglycolatebrothforbacteria,Sabouraud’sagarforfungiandnon-nutrientPage’ssalineagarforAcanthamoebawascarriedoutatthetimeoftheprocedure.Incubationtookplaceat37°Cfor48 hforbacteria,1weekforNocardiaand3weeksforfungi.Cultureplateswereexaminedusingroutinelaboratorytechniques.CultureplatesforAcanthamoebawereincubatedat30°C,wrappedinplasticbags,andexaminedintermittentlyforupto4weeksforthepresenceofcharacteristicdouble-walledstar-shapedcysts.ThiswaspreciselythesamemethodasthatusedfortheScottishCohortStudy.2

TheprevalenceofCLWinHongKonghasbeeninvestigatedbyChoetalandrecordedas6%with13%wearingrigidlenses.9Thepopulationbyagegroupforourareain1998wasprovidedbytheCensusandStatisticsDepartment,HongKongSpecialAdministrativeRegion.Thiscensusrecordedatotalof2 489 701persons,with2 048 630overtheageof15.Thislatterfigurewasusedasthereferencenumberforthetotalpopulationwhocouldbewearingcontactlenses.

TodeterminetheriskfactorsforCL-relatedMK,anestedcasecontrolstudywascarriedoutbyrecruiting206asymptomaticCLWvolunteerswithoralconsent.Onehundredandthirty-fivematchedourCLWpatientsforage（<25,26–35,36–45,and>45）,sex（maleorfemale）andeducationalstatus（graduate/non-graduate）.Onehundredandtwentyofthese135controlswerecommunity-basedwith102comingfromourLASIK（Laserin-situkeratomileusis）Clinic,12fromtheEyeScreening2000ClinicandsixfromKowloonopticalpractices（withthehelpoftheHongKongOptometricAssociation）.Fifteenmatchedcontrolswerehospital-basedlens-wearingasymptomaticstaffrecruitedatPWH.These135CLWvolunteerswerenotknowntorepresentanyspecificbias.Theresearchassistantface-to-faceinterviewedboththe45CLWpatientsand135volunteercontrolsusingthesamequestionnairestoestablishtheirtypesofCLWandhygienepractice.Questionsincludedthedurationoftimeofuseanduseinsleepduringdaytimeornighttime.

Forpatientandmatchedcontrolgroups,potentialriskfactorssuchasextendedwearofthelenswereevaluatedfortheirassociationwithMKbyunivariateandmultivariateconditionallogisticregressionanalyses.10Allriskfactorswerefirstassessedindividually,andmatchedoddsratios,thecorresponding95percentconfidenceintervalsandPvalueswerecalculated.RiskfactorswithP<0.25wereanalyzedbymultivariateanalysis10usingaforwardstepwiseselectionstrategy.Ingeneral,theprocessaddedthemostsignificantriskfactor（ietheonethatwouldresultinthelargestlikelihoodratiostatistic）tothemodelateachstep,andwouldcontinueuntilnoriskfactornotinthemodelmadeasignificant（P<0.05）contribution.WhenevertwoormorepotentialriskfactorswerehighlycorrelatedorP-valuesweresimilar,thefactorthatwasthemoreclinicallyorbiologicallyimportantwasselectedforentry.AnalyseswereperformedusingtheLogXactlogisticregressionsoftwarefeaturingexactmethods,version1.3（CYTELSoftwareCorporation,Cambridge,MA,USA）.