Medical Microbiology

Neisseria,Moraxella,andAcinetobacter 277

serogroupA,sometimesbyBstrainsaswelland,morerarely,bygroupC

strains.Serogroupsaredividedintoserovarsbasedondifferencesintheouter

membraneproteinantigens.

Pathogenesisandclinicalpicture.Meningococciareparasitesofthenaso-

pharynx.Thesemicroorganismsarecarriedby 5 – 10 %ofthepopulation.If

virulentmeningococcicolonizethenasopharyngealmucosaofahostlacking

theantibodies,pathogeninvasionofthemucosabymeansof“parasite-

directedendocytosis”becomespossible(seep. 1 2).TheCNSisdoubtless

thepreferredcompartmentforsecondaryinfections,althoughhematoge-

nouslydisseminatedpathogenscanalsoinfectthelungs,theendocardium,

ormajorjoints.

Onsetofthemeningitisisusuallysudden,afteranincubationperiodof

twotothreedays,withsevereheadache,fever,neckstiffness,andseverema-

laise.Severehemorrhagicsepsissometimesdevelops (Waterhouse-Frie-

drichsensyndrome).

Diagnosisrequiresdetectionofthepathogenincerebrospinalfluidorblood

bymeansofmicroscopyandculturingtechniques.Forsuccessinculturing,

thematerialmustbeusedtoinoculatebloodagarwithoutdelay.Identifica-

tionofthepathogenisbasedonidentificationofmetabolicproperties.The

slideagglutinationtestisusedtodeterminetheserogroup.

Latexagglutinationorcoagglutination(p. 21 7)canbeusedfordirectanti-

gendetectionincerebrospinalfluid.

Therapy.TheantibioticofchoiceispenicillinG.Verygoodresultshavealso

beenobtainedwiththird-generationcephalosporins,e.g.,cefotaximeorcef-

triaxone.Itisimportanttostarttreatmentasquicklyaspossibletoprevent

delayeddamage.

Theadvantageofcephalosporinsisthattheyarealsoeffectiveagainst

othermeningitispathogensduetotheirbroadspectrumofaction(with

theexceptionofListeriamonocytogenes).

Epidemiologyandprevention.Meningococcalinfectionsaremorefrequent

inthewinterandspringmonths.Transmissionofmeningococciisbydroplet

infection.Humansaretheonlypathogenreservoir.Sourcesofinfectionin-

cludebothcarriersandinfectedpersonswithmanifestdisease.Indeveloped

countries,meningitisoccurssporadicallyorintheformofminorepidemicsin

moreorlessisolatedcollectives(workcamps,recruitingcamps,schoolcamp-

ingfacilities).Theincidencelevelisapproximately 12 casesper 100000 in-

habitantsperyear.Inpartsofthedevelopingworld(Africanmeningitisbelt)

thelevelishigher.Lethalityrunsto 85 %ifthediseaseisleftuntreated,butis

reducedtolessthan 1 %iftreatmentisbegunearlyenough.Prophylactic

antibiosisisindicatedforthoseinclosecontactwithdiseasedpersons

(e.g.,inthesamefamily).Prophylacticmeasuresalsoincludetreatmentof

4

Kayser, Medical Microbiology © 2005 Thieme