Original article
Evaluation of the usefulness of a quantitative blood culture in the diagnosis of catheter-related bloodstream infection: Comparative analysis of two periods (2002 and 2012)Evaluación de la utilidad del hemocultivo cuantitativo en el diagnóstico de la bacteriemia relacionada con catéter: análisis comparativo de dos periodos (2002 y 2012)

https://doi.org/10.1016/j.eimc.2015.11.007Get rights and content

Abstract

Introduction

A retrospective study was conducted to investigate the usefulness of systematic quantitative blood culture (QBC) in the diagnosis of catheter-related bloodstream infection (CRBSI) during two 1-year periods (2002 and 2012).

Methods

The study included all QBC requests sent to the microbiology laboratory for suspected CRBSI in adults (≥18 years) with any type of intravascular catheter (IVC). Based on a ratio of ≥4:1 CFU/mL of the same microorganism between IVC blood culture from any lumen and peripheral blood culture, 5 diagnostic groups were defined: confirmed or probable CRBSI, primary BSI, other focus of infection, and colonization.

Results

In total, 4521 QBCs were evaluated; 24% positive in 2002 and 16% in 2012 (P < 0.0001). There were 243 episodes of suspected CRBSI (101 in 2002 and 142 in 2012). Confirmed CRBSI episodes were higher in 2002 than 2012 (56% vs 34%) (P < 0.0001), whereas colonization episodes were lower (18% vs 38%) (P = 0.0006). Gram-positive cocci decrease in 2012 relative to 2002 (56% vs 79.7%) (P = 0.022). Almost one-third (32%) of confirmed CRBSI would have been missed if blood from all catheter lumens had not been cultured.

Conclusions

QBC is a useful method for diagnosing CRBSI. Blood samples from all catheter lumens must be cultured to avoid missing around one-third of CRBSI diagnoses.

Resumen

Introducción

Se ha realizado un estudio retrospectivo, para investigar la utilidad del hemocultivo cuantitativo (HC) para el diagnóstico de las bacteriemias relacionadas con catéteres (BRC), durante dos periodos de un año (2002 y 2012).

Métodos

Todos los HC recibidos en el laboratorio de microbiología realizados ante la sospecha de BRC, a pacientes ≥18 años portadores de cualquier tipo de catéter intravascular (CIV), han sido incluidos en este estudio. Basándonos en la proporción ≥4:1 CFU/mL del mismo microorganismo entre el HC de cualquier luz del CIV y el HC periférico se han definido 5 grupos diagnósticos: BRC confirmada o probable, bacteriemia primaria, otro foco de infección y colonización.

Resultados

Han sido evaluados 4521 HC; 24% positivos en 2002 y 16% en 2012 (P < 0.0001). Fueron sospechosos de BRC 243 episodios (101 en 2002 y 142 en 2012). El Porcentaje de episodios de BRC confirmados fue mayor en 2002 que en 2012 (56% vs 34%) (P < 0.0001), en cambio fue menor el de los episodios de colonización (18% vs 38%) (P = 0.0006). Los cocos Gram-positivos disminuyeron en 2012 en relación con 2002 (56% vs 79.7%) (P = 0.022). En el 32.2% de las BRC confirmadas se hubiese perdido el diagnóstico si no se hubiera realizado HC de todas las luces.

Conclusiones

El HC es un método muy útil para el diagnóstico de las BRC. Hay que obtener muestra de sangre de todas luces para cultivo con el fin de evitar la pérdida de alrededor del 30% de los episodios de BRC.

Introduction

Intravascular catheters (IVCs) are commonly used in most medical centers. These devices are not only applied in hospitalized and emergency patients for administration of intravenous fluids or medication, but also in outpatients. A great variety of IVCs are available and all types are susceptible to colonization by microorganisms. The incidence of catheter-related bloodstream infection (CRBSI) is estimated at 0.1 to 5/1000 catheter-days.1, 2, 3, 4 Once a long-term catheter is successfully placed, attempts are made to maintain it as long as it is needed, as replacement is not without risk and another suitable vascular access may not be available.

Three methods are currently used for diagnosing CRBSI without removing the IVC: quantitative blood culture (pour plate method),5 semiquantitative blood culture (lysis-centrifugation),6, 7, 8, 9 and qualitative blood culture, using differential time to positivity on an automatic system.7, 8, 9, 10 Since 1988, quantitative blood culture (QBC) has been used in our center (sensitivity of 94%, specificity of 100%).5 The aims of this study are to determine the usefulness of this technique in two different periods: that is, to know what percentage of QBCs enable a microbiological diagnosis of CRBSI, to ascertain the IVC colonization rate in our setting, and to determine the percentage of CRBSI diagnoses that would have been missed if QBC had not been performed in all catheters or lumens in patients using several devices or IVCs with 2 or more lumens.

Section snippets

Material and methods

A retrospective observational study investigating the usefulness of our QBC method for the diagnosis of CRBSI was carried out in Vall d’Hebron Hospital (Barcelona, Spain), a 1000-bed reference hospital within the publically-funded health system. Two years were analyzed and compared: 2002 and 2012.

Results

A total of 4521 QBCs performed to investigate suspected CRBSI were included in the study, 1996 performed in 2002 (409 patients) and 2525 (1026 patients) in 2012. QBCs were positive in 24% (476/1996) in 2002 and 16% (415/2525) in 2012 (P < 0.0001). The larger number of QBCs performed in 2012 correspond to the Hematology Department (855 vs 638), Emergency Department (701 vs 45), and outpatient facilities (85 vs 10).

The percentage of positive QBCs in 2012 was found to have significantly decreased

Discussion

The present study, together with our previous one,5 has enabled us to confirm the continuing utility of the QBC technique applied in our hospital to diagnose or rule out CRBSI. Of particular note, the results illustrate the importance of obtaining samples from each and every lumen of the patient's IVCs to avoid missed diagnoses. Over the years we have continued to use the same criterion for the diagnosis of CRBSI: simultaneous QBCs in which the number of CFU/mL isolated from blood drawn from

Conflict of interest statement

The authors declare no conflict of interest.

Acknowledgments

The authors are grateful to the hospital nursing and the microbiology staff, to J.J. González-López for providing helpful comments during the writing of the manuscript and to C. Cavallo for language support.

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