Surveillance for Catheter‐Associated Bloodstream Infection in Hematology Units: Quantifyingthe Characteristics of a Practical Case Definition • Author(s): Leon J. Worth , MBBS, FRACP; James Black , MBBS, PhD; John F. Seymour ,MBBS, FRACP, PhD; Karin A. Thursky , MBBS, FRACP; Monica A. Slavin , MBBS, FRACPSource: Infection Control and Hospital Epidemiology, Vol. 29, No. 4 (April 2008), pp. 358-360Published by: The University of Chicago Press on behalf of The Society for Healthcare Epidemiologyof AmericaStable URL: http://www.jstor.org/stable/10.1086/528879 .

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infection control and hospital epidemiology april 2008, vol. 29, no. 4

c o n c i s e c o m m u n i c a t i o n

table 1. Comparison of Standard and Modified Case Defini-tions of Central Venous Catheter (CVC)–Associated BloodstreamInfection with the National Nosocomial Infection Surveillance Sys-tem (NNIS) Definition

NNIS casedefinition

Standard casedefinitiona

Modified casedefinitionb

Fulfilled Not fulfilled Fulfilled Not fulfilled

Fulfilled 18 0 18 0Not fulfilled 15 73 5 83

note. Data are no. of CVCs evaluated. A total of 106 CVCs (in 66patients) were evaluated.a Diagnosis by the treating physician based on routine microbiological testresults.b Diagnosis by treating physician but excluding cases not confirmed by apositive blood culture result.

Surveillance for Catheter-Associated

Bloodstream Infection in Hematology

Units: Quantifying the Characteristics

of a Practical Case Definition

Leon J. Worth, MBBS, FRACP;James Black, MBBS, PhD;John F. Seymour, MBBS, FRACP, PhD;Karin A. Thursky, MBBS, FRACP;Monica A. Slavin, MBBS, FRACP

We evaluated 66 patients in a hematology unit, who used a total of106 central venous catheters (CVCs), to identify CVC-associatedbloodstream infections using standard and modified surveillancecase definitions. Compared with the National Nosocomial InfectionSurveillance system criteria, a modified case definition used by treat-ing physicians demonstrated 100.0% sensitivity and 94.3% specific-ity. This case definition provides a practical method for effectivelyexcluding CVC-associated bloodstream infection.

Infect Control Hosp Epidemiol 2008; 29:358-360

A key requirement for effective surveillance of healthcare-associated infections is the use of standardized case defini-tions.1 A number of microbiological and clinical criteria maybe used for diagnosis of central venous catheter (CVC)–re-lated bloodstream infection (BSI), and various case defini-tions have previously been used.2,3 For CVC-associated BSI,the application of a standardized surveillance definition inhematology units has not yet been achieved.4

The objective of this study was to determine which casedefinition for CVC-associated BSI is practical for, and/orsuited to, monitoring patients at a hematology unit in anAustralian hospital. We determined the detection rate of clin-ically defined CVC-related BSI and the sensitivity, specificity,positive predictive value (PPV), and negative predictive value(NPV) of a novel surveillance definition of CVC-associatedBSI, compared with the National Nosocomial Infection Sur-veillance (NNIS) system definition. The impact of practicalmodifications to this definition was also analyzed.

methods

Setting and participants. This prospective, observationalstudy was performed in a single hematology unit during a 6-month period. The study population was defined as adultinpatients with hematologic malignancy who were expectedto develop neutropenia (defined as an absolute neutrophil

count of less than 0.5 # 109/L for 7 days or more) at sometime after insertion of a medium- or long-term CVC. Con-secutively inserted CVCs during the period from May 11through November 10, 2005, were reviewed. The study wasapproved by the institutional human ethics review committee.

A standardized protocol was used for exit-site dressing,flushing of catheters, and administration of heparin lock so-lution. The policy for management of febrile neutropeniaincluded the culture of 3 sets of blood samples collected afterthe onset of fever in neutropenic patients (1 peripheral and1 drawn from each lumen of a double-lumen CVC). All mi-crobiologic processing, including blood cultures, semiquan-titative catheter-tip cultures, and reporting of differential timeto positivity, was performed by a single accredited laboratory.Patients were assessed at least weekly until the end of the 6-month study period, until a complication necessitated CVCremoval (eg, infection, thrombosis, or occlusion), until theCVC was removed after completion of chemotherapy, or untildeath. A weekly review was performed of all in situ CVCs,regardless of whether a patient remained an inpatient or waslater discharged from the hospital or treated in an ambulatorycare setting.

Case definitions. The performance characteristics of 3 sep-arate case definitions were explored using data collected atweekly review. First, the clinical definition of intravascularcatheter–related infection used by the Infectious Diseases So-ciety of America (IDSA) was applied.5 Second, the NNIS sys-tem definition for CVC-associated BSI was applied.6 Infec-tions were subclassified according to which of the NNISsystem diagnostic criteria were fulfilled. Criterion 1 was thatthe patient had a recognized pathogen cultured from 1 ormore blood samples unrelated to infection at another site.Criterion 2A was that the patient had a common skin con-taminant cultured from 2 or more blood samples drawn on

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cvc-associated bsi in hematology units 359

table 2. Diagnostic Accuracy of the Standard and the Mod-ified Case Definitions of Central Venous Catheter–AssociatedBloodstream Infection, in Comparison With the Case Definitionof the National Nosocomial Infection Surveillance (NNIS) System

CharacteristicStandard case

definitiona

Modified casedefinitionb

Sensitivity, % (95% CI) 100.0 (81.5-100) 100.0 (81.5-100)Specificity, % (95% CI) 83.0 (73.5-90.1) 94.3 (87.2-98.1)PPV, % (95% CI) 54.6 (36.4-71.9) 78.3 (56.3-92.5)NPV, % (95% CI) 100.0 (95.1-100) 100.0 (95.7-100)

note. CI, confidence interval; NPV, negative predictive value; PPV,positive predictive value.a Diagnosis by the treating physician based on routine microbiologicaltest results.b Diagnosis by treating physician but excluding cases not confirmed bya positive blood culture result.

figure. Summary of diagnoses made with clinical and surveil-lance definitions for central venous catheter (CVC)–associatedbloodstream infection (BSI) in 66 patients who used a total of 106central venous catheters. There were 33 cases of CVC-associated BSI,of which 18 met National Nosocomial Infection Surveillance (NNIS)system criteria and 8 met the Infectious Diseases Society of America(IDSA) clinical definition.

separate occasions. Criterion 2B was that the patient had acommon skin contaminant cultured from blood, and the phy-sician instituted appropriate antimicrobial therapy. An infec-tion control practitioner and an infectious diseases physicianreviewed each case to check for fulfillment of criteria forclinical and NNIS definitions. Third, a modified case defi-nition of possible CVC-associated BSI used by treating phy-sicians was proposed, and this required the clinician (1 of 6hematologists) to have documented the initiation of anti-microbial therapy for CVC-associated BSI and/or removedthe catheter for this indication. Results of routine microbi-ological investigations were available to guide this decision.

Statistical analysis. We constructed 2 # 2 analysis tables,using the fulfillment of NNIS system criteria as the “goldstandard.” Exact binomial confidence intervals were deter-mined for calculated sensitivities, specificities, and predictivevalues using Stata statistical software, version 9.0 (Stata).

results

We evaluated 66 patients and a total of 106 CVCs (75 pe-ripherally inserted and 31 nontunneled), corresponding to atotal of 2,399 CVC-days. Eight cases that were clinically de-fined by the IDSA criteria as CVC-related BSI were observed(overall rate, 3.3 cases per 1,000 CVC-days [95% confidenceinterval, 1.4-6.6 cases per 1,000 CVC-days]).

In 18 cases, the criteria for CVC-associated BSI, accordingto the NNIS system definition, were fulfilled as follows: 11(61.1%) fulfilled criterion 1; 2 (11.1%) criterion 2A; and 5(27.8%) criterion 2B.

In 33 cases, the treating physicians determined that CVC-associated BSI was present. In 23 of these cases, diagnosiswas based on blood culture results. The pathogens isolatedwere as follows: coagulase-negative staphylococcus (10 cases),multiple pathogens (5), Bacillus species (2), Escherichia coli(2), Candida species (1), Klebsiella pneumoniae (1), methi-cillin-susceptible Staphylococcus aureus (1), and Enterobacter

cloacae (1). The remaining 10 cases were determined solelyon the basis of clinical findings (eg, the patient had a feverof unknown origin during the time in situ CVC was in place).Compared with the NNIS system definition, the diagnosismade by the treating physician had a sensitivity of 100.0%,a specificity of 83.0%, a PPV of 54.6%, and an NPV of 100.0%(Tables 1 and 2).

When the diagnosis of the treating physician was modifiedto exclude patients who did not have positive microbiologicaltest results, the modified case definition had a sensitivity of100.0%, a specificity of 94.3%, a PPV of 78.3%, and an NPVof 100.0% (Tables 1 and 2).

All clinically defined CVC-related BSIs were also classifiedas CVC-associated BSIs according to the NNIS system defi-nition. Cases diagnosed by the treating physicians were in-clusive of all CVC-associated BSIs that fulfilled NNIS systemcriteria (Figure).

discussion

The present study compares different case definitions forCVC-associated BSI in the hematology ward and raises theissue of a trade-off between accuracy and resource commit-ment for surveillance. Application of a standardized case def-inition by appropriately trained staff is necessary for robustand reliable monitoring of healthcare-associated infections.7,8

For neurosurgical procedures, passive surveillance by neu-rosurgeons has been shown to fail to capture cases of surgicalsite infection, compared with active surveillance by infectioncontrol professionals.9 In contrast, our study of a passivestrategy for surveillance of CVC-associated BSI in a hema-

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360 infection control and hospital epidemiology april 2008, vol. 29, no. 4

tology unit showed satisfactory case detection and excellentsensitivity.

Our evaluation of the IDSA clinical definition, the NNISsystem definition, and a modified case definition based onthe diagnosis of the treating physician were progressivelymore sensitive and less specific, and there was no false-neg-ative classification of cases with any of the surveillance def-initions. It is well established that clinical criteria for thedefinition of CVC-related BSIs are more specific than sur-veillance criteria, which is consistent with our data.

We applied the NNIS system definition as the “gold stan-dard,” given its widespread application and utility in intensivecare units for surveillance of CVC-associated BSI.10 Empiricaluse of antibiotics in a hematology unit may mean that theNNIS system criterion of “physician institutes appropriateantimicrobial therapy” is overrepresented, leading to a pos-sible overestimation of the infection rate. Our findings, how-ever, suggest that most NNIS system–defined infections inthe study population were made on the basis of criterion 1,in which a recognized pathogen was identified.

A limitation of the present study is the fact that a mixedgroup of treating physicians was responsible for the clinicaldecisions that were made in the hematology unit, and it wasnot possible to measure the degree of heterogeneity in clinicalpractice among the individual clinicians. Nevertheless, theproposed definition may be of value for institutional moni-toring of patients and could remove the need for a dedicatedinfection control practitioner or for a review by a clinicalmicrobiologist or infectious diseases physician. A modifiedcase definition of possible CVC-associated BSI in which thediagnoses of treating physicians required documentation ofculture-positive blood samples increased the PPV (from54.6% to 78.3%) without varying the sensitivity (100.0%).Because such a definition may depend on the in-house clinicalpractices and local expertise, it would be necessary for anycenter that wants to explore the validity of this approach tofirst obtain data for comparison with an accepted case def-inition. Further, given the small number of cases studied,larger confirmatory studies are required before the applica-tion of this particular case definition at multiple institutions.

Selection of an optimal case definition for surveillance pur-poses should be made with consideration of its sensitivity,specificity, and predictive value. The utility of a case definitionalso depends on the ease of its application and the resourcesit requires. We propose methods for analysis of novel andpractical case definitions for CVC-associated BSI in the he-matology ward and show that, within an institution, clinician-determined CVC-associated BSI may be as useful as more

complex and resource-intensive definitions for surveillanceof CVC-associated BSI.

acknowledgments

We are grateful to Stephen Burden (from the Peter MacCallum Cancer Cen-tre) for assistance with data collection.

Potential conflicts of interest. All authors report no conflicts of interestrelevant to this article.

From the Department of Infectious Diseases, Peter MacCallum CancerCentre, East Melbourne (L.J.W., J.F.S., K.A.T., M.A.S.), the Centre for ClinicalResearch Excellence Infectious Diseases, Victorian Infectious Diseases Service,(L.J.W., J.B., K.A.T., M.A.S.) and the Nossal Institute for Global Health,University of Melbourne (J.B.), Parkville, and the Department of Medicine,University of Melbourne, Fitzroy (J.F.S.), Victoria, Australia.

Address reprint requests to Leon J. Worth, FRACP, Department of Infec-tious Diseases, Peter MacCallum Cancer Centre, St. Andrew’s Place, EastMelbourne, Victoria, Australia 3002 (leon.worth@petermac.org).

Received October 2, 2007; accepted December 17, 2007; electronicallypublished February 28, 2008.

� 2008 by The Society for Healthcare Epidemiology of America. All rightsreserved. 0899-823X/2008/2904-0012$15.00. DOI: 10.1086/528879

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