院内感染革兰阴性菌血症：铜绿假单胞菌何时应引起怀疑？

背景：铜绿假单胞菌是无严重免疫缺陷患者社区获得性菌血症的罕见病因。由于限制抗铜绿假单胞菌药物不必要使用与避免不恰当治疗的延误之间存在紧张关系，临床医生需要关于何时经验性地治疗铜绿假单胞菌的更好的指导。我们试图确定院内感染铜绿假单胞菌菌血症发生率并建立模型加以预测。方法：在4所三级护理医院进行前瞻性研究。搜索微生物学数据以发现所有入院≤48h革兰阴性杆菌（GNRs）引起的菌血症发作。从病案室提取151例铜绿假单胞菌菌血症患者数据和152例随机选择的肠杆菌科菌血症患者数据。采用logistic回归鉴定有差异的参数，并计算患有铜绿假单胞菌菌血症的可能性。结果：铜绿假单胞菌引起4114例患者中6.8%患者出现院内GNR菌血症发作（发病率：5例/10000住院患者）。铜绿假单胞菌菌血症的独立预测因子是严重的免疫缺陷、年龄大于90岁、在过去的30天内接受抗菌疗法、放置中心静脉导管或泌尿设备。在250例无严重免疫缺陷患者中，如果无预测因子变量存在，患有铜绿假单胞菌菌血症的可能性是1:42。如果存在≥2个预测因子，患有铜绿假单胞菌菌血症的风险增加到1:3。结论：无严重免疫缺陷患者出现院内铜绿假单胞菌菌血症非常少见。对具有免疫能力的、具有≥2个预测因子的GNR菌血症患者，经验性地应用抗铜绿假单胞菌治疗是正当的。

专家评价：GaryGarberwithGregoryRoseOttawaHospital,CanadaInfectiousDiseasesAsimpledecisionrulemayguidethedecisiontoempiricallytreatforPseudomonaswhenGram-negativebacteremiaissuspected.Pseudomonalbacteremiaisrareinnewlyadmittedpatients,andempiricantipseudomonaltherapyisoverused.Thisstudywillprovehelpfulforantimicrobialstewardship.Theuseofempiricantipseudomonaltherapyforrecentlyadmittedpatientsisadouble-edgedsword.Overuseofourlimitedanti-pseudomonalarmamentariumleadstopathogenresistance{1};yet,undertreatmentofpseudomonaldiseasehasdisastrousconsequences{2}.UsingempiricantipseudomonaltherapyforasuspectedGram-negativebacteremiaisstraightforwardinimmunocompromisedpatients,anddecisionrulesexistforhospital-acquireddisease,butnonesofarfordiseaseemergingearlyinhospitaladmission.Theauthorsperformedanestedcase-controlstudy,selecting151casesofpseudomonalbacteremiaand152controlsfromamonga5-year,multinational,retrospectivecohortofpatientswithGram-negativebacteremiaidentifiedsoonafteradmission.Theyusedstepwiselogisticregressiontoidentify5factorsindependentlyassociatedwithpseudomonalbacteremia--severeimmunocompromise,age>90years,indwellingurinarytractdevice,centralvenouscatheter,orrecentuseofantimicrobials.Excludingsevereimmunocompromiseasastatemandatingantipseudomonaltherapy,theyconstructedadecisionrule.Using2ormorepredictorsasthedecisionpoint,thenumberneededtotreatforofferingantipseudomonaltherapyis3.Anargumentcouldbemadeforamorequantitativeapproachtoclinicaldecisionrule（CDR）derivation,butthecurrentrulehastheadvantageofsimplicity--animportantpointgiventhatearlyempirictherapyisnotoftentheprovinceofinfectiousdiseasespecialists.ThereportedpredictorsalsostandtoreasonandappearmoreusefulthanthosefoundinarecentretrospectivecohortanalysisbyCheongandcolleagues{3}.Schechner’spredictors,inouropinion,havetheadvantageastheyexcludeneutropenia（forwhichantipseudomonaltherapyisalreadyindicated）andaremoresimpletoconfirmthanthepresenceofshockorhealthcare-acquiredinfection.ThebigdrawbacktobothofthesestudiesisthepresupposedsuspicionofGram-negativebacteremia.Thissuspicionisofpoorspecificityinearlysepsis.Prospectivevalidationstudiesshouldbeundertakenamongabroadercohortpatientspresentingwithsepsis.