Relevance of the Number of Positive Bottles in Determining Clinical Significance of Coagulase-Negative Staphylococci in Blood Cultures

Abstract

Coagulase-negative staphylococci (CNS) are the most commonly isolated contaminants from blood cultures, yet they frequently cause true infections. Determining the clinical significance of CNS is difficult, and clinicians often consider the number of positive bottles within a set of blood culture bottles in their assessment. Therefore, in three separate studies, we counted the number of positive bottles within blood culture sets comprising two, three, or four bottles in order to predict whether or not CNS were clinically significant isolates (CSI) in adult patients with suspected sepsis. Each culture was evaluated by independent, published clinical criteria to determine its clinical importance. Of 486 positive sets that included two adequately filled bottles, 127 (26%) CNS were CSI, 329 (67%) were contaminants, and 30 (6%) were indeterminate as a cause of sepsis. Among CSI, 39 and 61% were isolated from one and two bottles, respectively. The positive predictive value for sepsis was 18% when one bottle was positive and 37% when both bottles were positive. Of 235 positive sets that included three adequately filled bottles, 81 (34%) were CSI, 109 (46%) were contaminants, and 45 (19%) were indeterminate as a cause of sepsis. Of CSI, 43, 38, and 19% were found in one, two, and three bottles, respectively. The positive predictive value for sepsis was 28, 52, and 30% when one, two and three bottles were positive. Of 303 positive blood culture sets that included four adequately filled bottles, 64 (21%) were considered CSI, 197 (65%) were contaminants, and 42 (14%) were indeterminate as a cause of sepsis. Of CSI, 27, 28, 19, and 27% were found in one, two, three, and four bottles, respectively. The positive predictive value for sepsis was 11, 30, 34, and 37% when one, two, three, and four bottles were positive. We conclude that the number of culture bottles positive in a given culture set cannot reliably predict the clinical significance of the CNS isolated and, therefore, should not be used as a criterion for determining whether or not an isolate represents true infection or contamination.Coagulase-negative staphylococci (CNS) are the most commonly isolated contaminants from blood cultures (12). Contaminated blood cultures result in increased lengths of stay and higher pharmacy, laboratory, and total costs (1). Determining the clinical significance of CNS is difficult, and some clinicians and microbiologists consider the number of positive bottles within a blood culture set in their assessment (4, 6-8). Our laboratories have accumulated data on CNS while participating in several multicenter, controlled clinical evaluations of blood culture media and systems (9, 10, 13). In this report, we review the data from these studies to determine whether the number of positive bottles within a blood culture set was useful for determining whether or not CNS were clinically significant isolates (CSI).(This work was presented, in part, at the 93rd General Meeting of the American Society for Microbiology, Atlanta, Ga., MATERIALS AND M...

Evaluation of Three Rapid Methods for the Direct Identification of Staphylococcus aureus from Positive Blood Cultures

“…The majority of these are coagulase-negative staphylococci (CoNS), many of which are not clinically significant and are likely contaminants (5,8,13,15). Thus, timely differentiation of staphylococci in blood cultures is instrumental in deciding on the use of empirical antimicrobial therapy.…”

Comparison of Demographic and Some Clinical Features of Patients Whose Blood Cultures Revealed Growth of Coagulase Negative Staphylococci and Differentiation Between Infectious Agent and Contaminant was Performed According to the CDC Criteria

“…Yeterli sayıda kan kültürü gönderilme-yen hastalarda, hastanın doktorunun ya da enfeksiyon kontrol ekibi doktorunun hastada sepsis bulgularının varlığını düşünmesi ve başka enfeksiyon odağının bulunmaması etkenin gerçek bakteriyemi etkeni olarak değerlendirilmesini sağladı. Çalışmamıza benzer şekilde daha önce yapılan farklı çalışmalarda, tek set kan kültüründe KNS üremesinin her zaman kontaminant olarak değerlendirilmemesi gerektiği bildirilmiş (9,10) ve bu nedenle CDC kriterlerinin klinik tanıdaki yerinin sorgulanması önerilmiştir.…”

Identification of Staphylococci Directly from Positive Blood Culture Bottles by MALDI-TOF MS System

“…S.aureus ve KNS'ler gram-pozitif koklar arasında en sık olarak izole edilen mikroorganizmalardır 13 . Tedavinin uygun yönlendirilmesi için S.aureus ile ilişkili KAE ile diğer stafilokok türlerinin neden olduğu kontaminasyonların birbirinden ayrılması ve stafilokok izolatlarının tür düzeyinde tanımlanması önemlidir 3 . KAE'ye neden olan mikroorganizmaların hızlı ve doğru tanım-lanmasının, uygun antibiyotik kullanımını sağladığı, hasta ölüm oranını ve hasta yatış günü sayısını düşürdüğü ve böylece hasta maliyetini azalttığı birçok araştırmacı tarafın-dan vurgulanmıştır 14,15 .…”

“…Stafilokok türleri klinik mikrobiyoloji laboratuvarlarında kan kültürü örneklerinden en sık olarak izole edilen mikroorganizmalardır 1 . Stafilokok türleri arasında Staphylococcus aureus, hem hastane hem de toplum kaynaklı enfeksiyonlar oluşturması ve virülansının yüksek olması nedeniyle önem kazanırken, koagülaz-negatif stafilokoklar (KNS) da KAE'den sıklıkla izole edilmektedir 2,3 . Septik şok aşamasının ilk altı saati içerisinde antibiyotik tedavisinin gecikmesi, hastanın yaşama oranını her saat için %7.6 oranında düşürmektedir 4 .…”