Medical Microbiology

NosocomialInfections 345

hospital.Theprevalenceofnosocomialinfectionsincreaseswiththesizeof

thehospital.Withinaparticularhospital,theinfectionrateisalwayshighest

intheintensivecareunits.

SourcesofInfection,TransmissionPathways

Nosocomialinfectionsoriginateeitherfromthepatient’sownflora(endo-

genousinfections)orfromexternalsources(exogenousinfections).Endo-

genousinfectionsarethemorefrequenttype.Insuchcases,thepatient

mayhavebroughtthepathogensintothehospital.Itis,however,frequently

thecasethatapatient’sskinandmucosaarecolonizedwithinonetotwodays

bybacteriaofthehospitalflora,whichoftenshowsmultipleresistanceto

antibioticsandreplacesthepatient’sindividualflora,andthatmostendogen-

ousinfectionsarethenactuallycausedbythespecifichospitalflora.The

sourceofinfectionforexogenousinfectionsismostlikelytoliewiththe

medicalstaff.Inmostcases,thepathogensaretransmittedfrompatient

topatientduringmedicalandnursingactivities.Lessfrequently,thestaff

iseitheralsoinfectedorcolonizedbythehospitalflora.Anotherimportant

causeofnosocomialinfectionsistechnicalmedicalmeasuresthatfacilitate

passageofthepathogensintothebody.Allinvasivediagnosticmeasurespre-

sentinfectionrisks.Thepatient’ssurroundings,i.e.,theair,floor,orwallsof

thehospitalroom,arerelativelyunimportantassourcesofinfection.

Control

Themeasurestakentocontrolandpreventnosocomialinfectionscorrespond

inthewidersensetothegeneralmethodsofinfectioncontrol.Themany

differentindividualmeasureswillnotbelistedhere.Theinfectioncontrol

programvariesdependingonthesituationineachparticularhospitaland

canbesummarizedinthreegeneralgroups:

Operationalmeasures.Thiscategoryincludesallmeasurespertainingto

treatmentandcareofpatientsandcleaningmeasures.Thisincludesasepsis,

disinfection,sterilization,andcleaning.Furtherprecautionaryoperational

measuresincludeisolationofpatientsthatwouldbesourcesofinfection

andtheeconomicalandspecificadministrationofantibiotictherapies.

Organizationalmeasures.Theorganizationofhospitalinfectioncontrol

mustbeadaptedtothestructureofeachparticularhospital.Realizationof

thenecessarymeasures,whichofcoursealwaysinvolveworkingtimeand

expense,isbestrealizedbyestablishinganinfectioncontrolcommittee

chargedwiththefollowingtasks:determinationandanalysisofthesituation,

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Kayser, Medical Microbiology © 2005 Thieme