Simple indictor of increased blood culture contamination rate by detection of coagulase-negative staphylococci

Kei Yamamoto,Kazuhisa Mezaki,Norio Ohmagari

doi:10.1038/s41598-021-96997-y

Kei Yamamoto, Kazuhisa Mezaki + Show 1 more

Open Access

https://doi.org/10.1038/s41598-021-96997-y

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Abstract

Coagulase-negative staphylococci (CoNS) are the most frequent contaminating bacteria; therefore, we aimed to investigate an indicator of CoNS to predict the increase in blood culture contamination rate (ConR). We performed a retrospective study of selected patients, who underwent blood culture testing. Contamination was defined as the presence of either one of two or more sets of skin-resident bacteria, except for cases with a low likelihood of contamination based on clinical aspects. We calculated the monthly ConR [(total number of contaminated cases per month)/(total number of blood culture sets collected per month) × 100] and analysed the ConR prediction ability using the following four indicators: the number of CoNS-positive sets of blood cultures, cases with at least one CoNS-positive blood culture set, cases with only one CoNS-positive blood culture set, and cases of contamination by CoNS. Cases with CoNS-positive blood cultures correlated with ConR (r = 0.85). Although the area under the receiver operating characteristic curve for the number of cases with ConR ≥ 2.5 differed significantly from that of the number of cases contaminated by CoNS, the negative predictive value was high, reaching up to 95.5% (95% confidential interval 87.3–99.1). The number of CoNS-positive cases could help predict an increase in ConR ≥ 2.5.

Highlights

Coagulase-negative staphylococci (CoNS) are the most frequent contaminating bacteria; we aimed to investigate an indicator of CoNS to predict the increase in blood culture contamination rate (ConR)
CoNS was positive in 3126 sets, of which Staphylococcus epidermidis was included in 1771 sets (56.7%)
We compared the predictive ability of monthly contamination rate of 2.5 or higher depending on whether the detected organism was S. epidermidis or other CoNS for each sample, but there was no significant difference (AUC 0.784 vs. 0.801, p = 0.76, Supplementary Figure). These results suggest that the indicators A and B, which can be counted correlated with ConR to predict a ConR of ≥ 2.5, or higher, but their prediction ability was inferior to that of indicators C and D in multiple comparisons of Receiver operating characteristic (ROC) curves

Summary

Introduction

Coagulase-negative staphylococci (CoNS) are the most frequent contaminating bacteria; we aimed to investigate an indicator of CoNS to predict the increase in blood culture contamination rate (ConR). Relevant culture tests are important for the appropriate use of antimicrobial agents to combat antimicrobialresistant bacteria. These tests can result in increased contamination, leading to an excessive use of antimicrobial agents, contributing to longer hospital stays and higher costs[1,2]. The blood culture contamination rate (ConR) is calculated retrospectively based on certain c riteria[3]; its calculation is time-consuming and requires additional labour. Coagulase-negative staphylococci (CoNS) are the most frequently detected bacteria in blood culture c ontamination[2]. The values of the four indicators were aggregated as follows: the number of CoNS-positive sets of blood cultures, cases with at least one CoNS-positive blood culture set, cases with only one CoNS-positive blood culture set, and cases of contamination by CoNS

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