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 Table of Contents  
Year : 2021  |  Volume : 9  |  Issue : 2  |  Page : 62-65

Role of single, paired and multiple specimens in the outcome of automated blood culture system – A 2 years study from South India

Department of Microbiology, Manipal Hospital, Bengaluru, Karnataka, India

Date of Submission22-Jul-2021
Date of Acceptance23-Nov-2021
Date of Web Publication1-Feb-2022

Correspondence Address:
Dr. Aravinda Anjana
Department of Lab Medicine- Microbiology, Manipal Hospital, Bengaluru - 560 017, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jpsic.jpsic_17_21

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Automated blood culture (BC) system remains the best approach for early definitive management of sepsis. A retrospective analysis of samples received over 2 years was done to compare the sensitivity of single, paired and multiple BC sets. A total of 24,955 samples were received, of which 11,355 were single, 12,555 were paired and 1045 were multiple. BC sensitivity increased from 32.3% to 87% when samples increased from one to two, and a rise of another 13% with four sample sets (P < 0.0001). There is higher chance of missing positives if only a single BC sample was collected.

Keywords: Automation, blood culture, multiple set, paired, sepsis

How to cite this article:
Anjana A, Ranjeeta A, Bhavana MV, Beena HB. Role of single, paired and multiple specimens in the outcome of automated blood culture system – A 2 years study from South India. J Patient Saf Infect Control 2021;9:62-5

How to cite this URL:
Anjana A, Ranjeeta A, Bhavana MV, Beena HB. Role of single, paired and multiple specimens in the outcome of automated blood culture system – A 2 years study from South India. J Patient Saf Infect Control [serial online] 2021 [cited 2022 Jun 30];9:62-5. Available from: https://www.jpsiconline.com/text.asp?2021/9/2/62/337090

  Introduction Top

Bloodstream infection (BSI) is a leading cause of morbidity and mortality, especially in critically ill patients. Although difficult to ascertain, a recent study reported 48.9 million sepsis cases and 11 million sepsis-related deaths worldwide in 2017, accounting for almost 20% of global deaths. Significant regional disparities in sepsis incidence and mortality exist; approximately 85% being attributed to low- and middle-income countries.[1] Timely management with appropriate antimicrobial therapy, in turn, can reduce mortality rates, length of hospital stay and costs. Rapid microbiological investigation and identification of the causative agent and antimicrobial susceptibility testing are therefore essential to adjust the anti-infectious therapy, avoid inappropriate treatment, de-escalate and limit the toxicity and negative impact on beneficial bacteria.[2] Despite continuous advances in molecular techniques and biomarkers, blood culture (BC) remains the gold standard for the diagnosis of BSI.[3] BC currently represents the main method to determine the aetiology of BSI because of its high sensitivity and easy to perform.[2]

Various automated continuous monitoring BC systems are available in clinical microbiology which can detect organisms faster and more frequently compared to older conventional methods. These automated platforms measure the rate of production of bacterium-specific metabolite in the BC bottle supplemented with nutrient broth. When the positive BC is taken as a starting point, microbial identification takes 24–72 h to complete.[4] Practice of paired aerobic/anaerobic BC utilises two atmospheres, maximising the yield of obligate aerobic, obligate anaerobic and facultative anaerobic microorganisms.

However, optimisation of the BC strategy is complex because it invariably depends on the bacterial load in the sample, the volume of blood, time of collection with regard to antibiotic instillation and the risk of contamination. Even the technical factors such as the culture media of the BC systems and the duration of incubation also play an equal role. The objective of the present study is to compare the BC performances of single (SBC), paired (PBC) and multiple BC (MBC) sets. We determined the comparative microbial yield and sensitivities of the same.

  Materials and Methods Top

A retrospective analysis of all BC samples of patients from a 600 bedded tertiary centre located in Southern India was done. The study was over 2 years from January 2018 to December 2019. All samples from suspected sepsis patients were included in the study. The samples were collected either as: SBC, PBC or MBC BC sets from the patients. In SBC, the sample was collected in only one aerobic BacT/ALERT 3D bottle, PBC set included a pair of aerobic and anaerobic bottles from a single venepuncture site collected at the same time and MBC set was a pair of aerobic and anaerobic bottles each from two different venepuncture sites collected at the same time. Blood samples were collected by the nursing staff or trained phlebotomist following strict aseptic precautions.

We compared the microbial yield and sensitivity of the three sets. Both bacteraemia and candidemia were taken into account. Nonduplicate consecutive isolates of the same were included in the analysis. Phenotypic confirmation of the isolated bacteria and yeast was done by conventional methods and automated VITEK 2 compact (BioMérieux, France) platform. AST was performed and interpreted following the Clinical and Laboratory Standards Institute guidelines.

All Gram-negative bacteria (GNB), Staphylococcus aureus, Streptococcus pneumoniae and yeast were defined as true pathogens causing bacteraemia or candidemia. Coagulase-negative Staphylococci, diphtheroids, Bacillus species, Micrococcus species or viridians Streptococci were defined as skin contaminants, if not isolated from two or more culture samples from different sites and associated with fever (body temperature >38.3°C), rigors or hypotension (systolic blood pressure <90 mm Hg).

  Results Top

We have analysed all BC samples received from January 2018 to December 2019. A total of 24,955 samples were received in our department of which 11,355 were SBC (45.5%), 12,555 were PBC (50.3%) and 1045 were MBC (4.2%). We have received samples from the intensive care unit, inpatient and outpatient departments. The mean age of the patients was 49.4 (±22.4) with a gender ratio (male:female) of 1.42.

A total of 3242 showed growth in at least one sample from a set, of which 2610 were true positives and 632 were skin contaminants. In SBC, true pathogens were 7.5% (n = 855) and skin contaminants were 1.7% (n = 192). In PBC, true pathogens were isolated in 11.3% (n = 1417) and skin contaminants in 2.8% (n = 357) whereas in MBC it was 32.3% (n = 338) and 7.9% (n = 83), respectively. Among the true pathogens, GNB (n = 1979, 75.8%) was the most predominant followed by Gram-positive cocci (GPC) (n = 507, 19.4%) and yeasts (n = 124, 4.8%). Of the true SBC positives; 722 were GNB, 114 were GPC and 19 were yeast. Similarly, in 1417 PBC positives, 1043 were GNB, 317 were GPC and 57 were yeast, and in MBC it was 214, 76 and 48, respectively. The cumulative data are given in [Table 1].
Table 1: Cumulative data on blood culture sets

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Among GNB, the most common was Escherichia coli (n = 604) followed by Klebsiella pneumoniae (n = 514). Among the non-fermenters, Acinetobacter species (n = 144) was the most predominant followed by Pseudomonas species including Pseudomonas aeruginosa (n = 111). Salmonella Typhi was isolated from 283 blood samples. Among GPC, S. aureus and Enterococcus species were isolated from 158 and 165 samples, respectively. Candidemia was mostly caused by Candida tropicalis (n = 42) followed by Candida albicans (n = 18) and Candida parapsilosis (n = 16). The true pathogen distribution is depicted in [Figure 1].
Figure 1: Distribution of true pathogens isolated

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We tried to analyse the sensitivities of the three BC sets. The sensitivity of the BC s increased from 32.3% to 87.0% when the number of samples was increased from one to two, and a rise of another 13% was seen when four samples were taken into consideration. Chi-square analysis revealed statistically significant difference between all three groups (P < 0.0001). The sensitivity of PBC, SBC and MBC was 9.22% (n = 11355), 14.13% (12555) and 41.07% (n = 1045), respectively.

  Discussion Top

Automated BC platforms significantly reduce the time required for the processing of samples and also facilitates yield of both Gram-negative and Gram-positive bacteria along with yeast and other rare organisms. Appropriate detection of the pathogen and minimum contamination are the two major goals for BC diagnostics. Therefore, the sampling strategy is essential to optimise its performance. The rationale of this strategy is based on the following points: (i) repetition of samples increases the total volume of blood cultured, thereby improving BC sensitivity, (ii) separate samples may discriminate contaminants from pathogens when BCs grow and (iii) separate samples improve BSI detection in case of intermittent bacteraemia.[5]

Multi-sampling strategy plays the cornerstone in the diagnosis of catheter-related BSI (CRBSI). It is defined as the presence of bacteraemia originating from an intravenous catheter. It is one of the most frequent, lethal and costly complications of central venous catheterisation and also the most common cause of nosocomial bacteraemia. CRBSI is attributed to an intravascular catheter by quantitative culture of the catheter tip or by differences in growth between the catheter and peripheral venepuncture BC specimens. Time to positivity has been demonstrated to be a reliable surrogate measure of the microbial load in the specimen of blood obtained for culture.[6]

There are many other similar studies on sampling strategy, which also concluded that as many as four BC sets over a 24-h period may be needed for >99% test sensitivity.[7],[8] Most of the available Indian literature to our knowledge is on smaller sample size. Elantamilan et al. (n = 1054) reported that sensitivity of the BC s increased from 85.67% to 96.59% when the number of samples was increased from one to two, and a rise of another 3.41% was seen when three samples were taken.[9] Tarai et al. also in 2012, in their study on total of 6903 samples, reported higher yield rates with paired BC when compared to single culture set.[10]

  Conclusion Top

In our study on 24,955 BC samples, significantly higher microbial yield and sensitivity were seen in MBC followed by PBC and SBC. Multi-sampling BC strategy enabled to differentiate between true positives and contamination. We hereby conclude that there is a higher chance of missing positives if only a single BC sample was collected. The number of samples collected from different venepuncture sites is a critical determinant of the outcome of BC systems.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Rudd KE, Johnson SC, Agesa KM, Shackelford KA, Tsoi D, Kievlan DR, et al. Global, regional, and national sepsis incidence and mortality, 1990-2017: Analysis for the Global Burden of Disease Study. Lancet 2020;395:200-11.  Back to cited text no. 1
Opota O, Croxatto A, Prod'hom G, Greub G. Blood culture-based diagnosis of bacteraemia: State of the art. Clin Microbiol Infect 2015;21:313-22.  Back to cited text no. 2
Lamy B, Dargère S, Arendrup MC, Parienti JJ, Tattevin P. How to optimize the use of blood cultures for the diagnosis of bloodstream infections? A state-of-the art. Front Microbiol 2016;7:697.  Back to cited text no. 3
Jansen GJ, Mooibroek M, Idema J, Harmsen HJ, Welling GW, Degener JE. Rapid identification of bacteria in blood cultures by using fluorescently labeled oligonucleotide probes. J Clin Microbiol 2000;38:814-7.  Back to cited text no. 4
Reimer LG, Wilson ML, Weinstein MP. Update on detection of bacteremia and fungemia. Clin Microbiol Rev 1997;10:444-65.  Back to cited text no. 5
Shah H, Bosch W, Thompson KM, Hellinger WC. Improving health care quality: Review. Neurohospitalist 2013;3:144-51.  Back to cited text no. 6
Cockerill FR 3rd, Wilson JW, Vetter EA, Goodman KM, Torgerson CA, Harmsen WS, et al. Optimal testing parameters for blood cultures. Clin Infect Dis 2004;38:1724-30.  Back to cited text no. 7
Lee A, Mirrett S, Reller LB, Weinstein MP. Detection of bloodstream infections in adults: How many blood cultures are needed? J Clin Microbiol 2007;45:3546-8.  Back to cited text no. 8
Elantamilan D, Lyngdoh VW, Khyriem AB, Rajbongshi J, Bora I, Devi ST, et al. Comparative evaluation of the role of single and multiple blood specimens in the outcome of blood cultures using BacT/ALERT 3D (automated) blood culture system in a tertiary care hospital. Indian J Crit Care Med 2016;20:530-3.  Back to cited text no. 9
  [Full text]  
Tarai B, Das P, Kumar D, Budhiraja S. Comparative evaluation of paired blood culture (aerobic/aerobic) and single blood culture, along with clinical importance in catheter versus peripheral line at a tertiary care hospital. Indian J Med Microbiol 2012;30:187-92.  Back to cited text no. 10
  [Full text]  


  [Figure 1]

  [Table 1]


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