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