Medical Microbiology

208 3 GeneralBacteriology

Preconditions,GeneralMethods,Evaluation.............

Preconditions..........................................

Thefieldofmedicalmicrobiologydealingwithlaboratorydiagnosisofinfec-

tiousdiseasesisknownasdiagnosticorclinicalmicrobiology.Modernmed-

icalpractice,andinparticularhospital-basedpractice,isinconceivablewith-

outthecooperationofaspecialmicrobiologicallaboratory.

Toensureoptimumpatientbenefit,thephysicianinchargeoftreatment

andthelaboratorystaffmustcooperatecloselyandefficiently.Theprecondi-

tionsincludeabasicknowledgeofpathophysiologyandclinicalinfectiology

onthepartofthelaboratorystaffandfamiliaritywiththelaboratoryworkon

thepartofthetreatingphysician.Thefollowingsectionsprovideabriefrun-

downonwhatphysiciansneedtoknowaboutlaboratoryprocedures.

GeneralMethodsandEvaluation.....................

Aninfectiousdiseasecanbediagnoseddirectlybyfindingthecausalpatho-

genoritscomponentsorproducts.Itcanalsobediagnosedindirectlyby

meansofantibodydetection(Chapter2,p. 12 1ff.).Theaccuracyandvalue

ofeachoftheavailablediagnosticmethodsarecharacterizedintermsofsen-

sitivity,specificity,andpositiveornegativepredictivevalue.Thesepara-

metersarebestunderstoodbyreferencetoa 2! 2 table(Table3. 6 ).

Byinsertingfictitiousnumbersintothe 2! 2 table,itreadilybecomes

apparentthatapositivepredictivevaluewillfallrapidly,despitehighlevels

ofspecificityandsensitivity,iftheprevalencelevelislow(Baye’stheorem).

SamplingandTransportofTestMaterial.................

Itisveryimportantthatthematerialtobetestedbecorrectlyobtained

(sampled)andtransported.Ingeneral,materialfromwhichthepathogen

istobeisolatedshouldbesampledasearlyaspossiblebeforechemotherapy

isbegun.Transporttothelaboratorymustbecarriedoutinspecialcontainers

providedbytheinstitutesinvolved,usuallycontainingtransportmediums—

eitherenrichmentmediums(e.g.,bloodculturebottle),selectivegrowth

mediumsor simpletransport mediumswithout nutrients.Aninvoice

mustbeattachedtothematerialcontainingtheinformationrequiredforpro-

cessing(usingtheformprovided).

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Kayser, Medical Microbiology © 2005 Thieme