Sultan Qaboos University Med J, May 2017, Vol. 17, Iss. 2, pp. e202–208, Epub. 20 Jun 17 Submitted 2 Aug 16 Revisions Req. 27 Sep & 4 Dec 16; Revisions Recd. 29 Oct 16 & 25 Jan 17 doi: 10.18295/squmj.2016.17.02.011 Accepted 26 Jan 17 c li n i c a l & b a s i c r e s e a r c h
Blood Culture Contaminants in a Paediatric Population Retrospective study from a tertiary hospital in Oman *Mohamed A. El-Naggari,1 Sharef W. Al-Mulaabed,1,3 Zakaria Al-Muharrmi,2 Renjith Mani,1 Rana Abdelrahim,1 Reem Abdwani1
ملوثات عزالت الدم املزروعة عند األطفال دراسة استعادية من مستشفى ثالثي يف عمان
رمي عبدواين، رنا عبد الرحيم، رجنيث ماين، زكريا املحرمي، �رشيف املال عبد،حممد النجاري abstract: Objectives: Most children presenting with febrile illness require a blood culture to determine the causative organism as well as its sensitivity to antibiotics. However, false-positive results lead to unnecessary hospitalisations, prescriptions and tests. This study aimed to evaluate the impact of false-positive blood cultures among a paediatric population at a tertiary hospital in Oman. Methods: This retrospective study included all 225 children 13 years old with documented positive blood cultures who presented to SQUH between July 2011 and December 2013. The blood cultures were taken as follows. A total of 2–5 mL of blood was collected from each patient through peripheral skin punctures after a standardised disinfection procedure. The blood samples inoculated in a BACTEC™/F line blood culture system (Becton, Dickinson and Company, Franklin
Lakes, New Jersey, USA), which is a fully-automated walk-away testing system that uses a continuous monitoring instrument to agitate and incubate blood cultures bottles. Subsequently, microbial identification and susceptibility tests were performed using standard methods.9 During the retrospective analysis, data on positive blood cultures were collected from the hospital information system and patient records. The blood culture results were then re-examined to determine whether they were true- or false-positives. Several organisms were immediately identified as significant or true-positive cultures because they are known to cause diseases in children.6,10,11 On the other hand, other organisms were presumed to be contaminants if they were rare or unusual causes of disease, particularly in the absence of any underlying disease in the patient, or identified among patients with intravascular catheters or indwelling vascular devices.6 Some organisms were considered equivocal and required a judgement decision by a clinical microbiologist to be classified as either pathogenic or a contaminant. In order to determine if a culture was true-positive, the following information was needed: the identity of the organism; the number of positive culture sets; the number of positive bottles within a set; the time needed for the organism to grow in the blood culture; the rate of growth in the blood culture; associated clinical and laboratory data; and the automated classification generated by the blood culture system.6,10,11 Table 1 shows the classification of various organisms as true-positive, false-positive or equivocal. The demographic and clinical data of the patients was also collected, including age, gender, the date of the blood culture collection, the presence of any underlying chronic illnesses, the degree of fever (if present), hospital admissions, length of hospital stay, focus of infection, antibiotic prescriptions and mortality. A focus of infection was defined as a clear associated source of the infection detected during history-taking or a clinical examination, without the need for blood cultures. A change in antibiotic therapy was defined as any modification or interruption of an antibiotic prescription after a blood culture result was
Clinical and Basic Research
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Blood Culture Contaminants in a Paediatric Population Retrospective study from a tertiary hospital in Oman
Table 1: Classification of organisms isolated from positive blood cultures as true-positive, equivocal* or false-positive according to standard criteria6,10,11 True-positive
Equivocal
False-positive
•Acinetobacter baumannii •Candida krusei •Candida tropicalis •Non-albicans Candida spp. •Citrobacter koseri •Enterobacter cloacae •Enterococcus durans •Enterococcus raffinosus •Escherichia coli •Haemophilus influenzae type B •Klebsiella oxytoca •Klebsiella pneumoniae •Morganella morganii •Neisseria meningitidis •Proteus mirabilis •Pseudomonas aeruginosa •Salmonella enterica subsp. enterica •Other Salmonella spp. •Serratia marcescens •Staphylococcus aureus •MRSA •Streptococcus bovis type II •Streptococcus pneumoniae •Streptococcus pyogenes
•Acinetobacter lwoffii •Acinetobacter haemolyticus •Alcaligenes faecalis •CDC group Vb-3 •Chryseobacterium indologenes •Chryseobacterium meningosepticum •Citrobacter amalonaticus •Delftia acidovorans •Diphtheroids •Empedobacter brevis •Enterococcus faecium •Moraxella spp. •Pantoea agglomerans •Pseudomonas spp. (including P. putida and P. stutzeri) •Sphingomonas paucimobilis •Staphylococcus capitis •Staphylococcus capitis subsp. ureolyticus •Staphylococcus epidermidis •Staphylococcus haemolyticus •Staphylococcus hominis •Other coagulase-negative Staphylococcus spp. •Stenotrophomonas maltophilia •Viridans streptococci
•Aerococcus viridans •Bacillus subtilis •Other Bacillus spp. •Brevundimonas diminuta •Dermabacter hominis •Dermacoccus nishinomiyaensis •Kocuria kristinae •Leifsonia aquatica •Micrococcus luteus •Other Micrococcus spp. •Propionibacterium acnes •Staphylococcus caprae •Staphylococcus intermedius •Staphylococcus lugdunensis •Staphylococcus pasteuri •Staphylococcus saprophyticus •Staphylococcus warneri •Streptococcus acidominimus •Streptococcus mitis •Streptococcus salivarius •Streptococcus sobrinus •Other Streptococcus spp.
CDC = Centers for Disease Control and Prevention; MRSA = methicillin-resistant Staphylococcus aureus. *A judgement decision as to whether these organisms are true pathogens or false-positive by a clinical microbiologist is needed.
reported. In addition, laboratory data at the time of blood collection were recorded, including white blood cell count (WBC), absolute neutrophil count (ANC) and C-reactive protein (CRP) levels. Data were analysed using the Statistical Package for the Social Sciences (SPSS), Version 20, (IBM Corp., Armonk, New York, USA). Percentages of true- and false-positive blood cultures were determined. A Chisquared test was used to compare categorical variables and an unpaired Student’s t-test or Mann-Whitney U test was used to compare numerical variables according to their normal distribution. The level of significance was set at an a priori two-tailed level of P
Blood Culture Contaminants in a Paediatric Population Retrospective study from a tertiary hospital in Oman *Mohamed A. El-Naggari,1 Sharef W. Al-Mulaabed,1,3 Zakaria Al-Muharrmi,2 Renjith Mani,1 Rana Abdelrahim,1 Reem Abdwani1
ملوثات عزالت الدم املزروعة عند األطفال دراسة استعادية من مستشفى ثالثي يف عمان
رمي عبدواين، رنا عبد الرحيم، رجنيث ماين، زكريا املحرمي، �رشيف املال عبد،حممد النجاري abstract: Objectives: Most children presenting with febrile illness require a blood culture to determine the causative organism as well as its sensitivity to antibiotics. However, false-positive results lead to unnecessary hospitalisations, prescriptions and tests. This study aimed to evaluate the impact of false-positive blood cultures among a paediatric population at a tertiary hospital in Oman. Methods: This retrospective study included all 225 children 13 years old with documented positive blood cultures who presented to SQUH between July 2011 and December 2013. The blood cultures were taken as follows. A total of 2–5 mL of blood was collected from each patient through peripheral skin punctures after a standardised disinfection procedure. The blood samples inoculated in a BACTEC™/F line blood culture system (Becton, Dickinson and Company, Franklin
Lakes, New Jersey, USA), which is a fully-automated walk-away testing system that uses a continuous monitoring instrument to agitate and incubate blood cultures bottles. Subsequently, microbial identification and susceptibility tests were performed using standard methods.9 During the retrospective analysis, data on positive blood cultures were collected from the hospital information system and patient records. The blood culture results were then re-examined to determine whether they were true- or false-positives. Several organisms were immediately identified as significant or true-positive cultures because they are known to cause diseases in children.6,10,11 On the other hand, other organisms were presumed to be contaminants if they were rare or unusual causes of disease, particularly in the absence of any underlying disease in the patient, or identified among patients with intravascular catheters or indwelling vascular devices.6 Some organisms were considered equivocal and required a judgement decision by a clinical microbiologist to be classified as either pathogenic or a contaminant. In order to determine if a culture was true-positive, the following information was needed: the identity of the organism; the number of positive culture sets; the number of positive bottles within a set; the time needed for the organism to grow in the blood culture; the rate of growth in the blood culture; associated clinical and laboratory data; and the automated classification generated by the blood culture system.6,10,11 Table 1 shows the classification of various organisms as true-positive, false-positive or equivocal. The demographic and clinical data of the patients was also collected, including age, gender, the date of the blood culture collection, the presence of any underlying chronic illnesses, the degree of fever (if present), hospital admissions, length of hospital stay, focus of infection, antibiotic prescriptions and mortality. A focus of infection was defined as a clear associated source of the infection detected during history-taking or a clinical examination, without the need for blood cultures. A change in antibiotic therapy was defined as any modification or interruption of an antibiotic prescription after a blood culture result was
Clinical and Basic Research
| e203
Blood Culture Contaminants in a Paediatric Population Retrospective study from a tertiary hospital in Oman
Table 1: Classification of organisms isolated from positive blood cultures as true-positive, equivocal* or false-positive according to standard criteria6,10,11 True-positive
Equivocal
False-positive
•Acinetobacter baumannii •Candida krusei •Candida tropicalis •Non-albicans Candida spp. •Citrobacter koseri •Enterobacter cloacae •Enterococcus durans •Enterococcus raffinosus •Escherichia coli •Haemophilus influenzae type B •Klebsiella oxytoca •Klebsiella pneumoniae •Morganella morganii •Neisseria meningitidis •Proteus mirabilis •Pseudomonas aeruginosa •Salmonella enterica subsp. enterica •Other Salmonella spp. •Serratia marcescens •Staphylococcus aureus •MRSA •Streptococcus bovis type II •Streptococcus pneumoniae •Streptococcus pyogenes
•Acinetobacter lwoffii •Acinetobacter haemolyticus •Alcaligenes faecalis •CDC group Vb-3 •Chryseobacterium indologenes •Chryseobacterium meningosepticum •Citrobacter amalonaticus •Delftia acidovorans •Diphtheroids •Empedobacter brevis •Enterococcus faecium •Moraxella spp. •Pantoea agglomerans •Pseudomonas spp. (including P. putida and P. stutzeri) •Sphingomonas paucimobilis •Staphylococcus capitis •Staphylococcus capitis subsp. ureolyticus •Staphylococcus epidermidis •Staphylococcus haemolyticus •Staphylococcus hominis •Other coagulase-negative Staphylococcus spp. •Stenotrophomonas maltophilia •Viridans streptococci
•Aerococcus viridans •Bacillus subtilis •Other Bacillus spp. •Brevundimonas diminuta •Dermabacter hominis •Dermacoccus nishinomiyaensis •Kocuria kristinae •Leifsonia aquatica •Micrococcus luteus •Other Micrococcus spp. •Propionibacterium acnes •Staphylococcus caprae •Staphylococcus intermedius •Staphylococcus lugdunensis •Staphylococcus pasteuri •Staphylococcus saprophyticus •Staphylococcus warneri •Streptococcus acidominimus •Streptococcus mitis •Streptococcus salivarius •Streptococcus sobrinus •Other Streptococcus spp.
CDC = Centers for Disease Control and Prevention; MRSA = methicillin-resistant Staphylococcus aureus. *A judgement decision as to whether these organisms are true pathogens or false-positive by a clinical microbiologist is needed.
reported. In addition, laboratory data at the time of blood collection were recorded, including white blood cell count (WBC), absolute neutrophil count (ANC) and C-reactive protein (CRP) levels. Data were analysed using the Statistical Package for the Social Sciences (SPSS), Version 20, (IBM Corp., Armonk, New York, USA). Percentages of true- and false-positive blood cultures were determined. A Chisquared test was used to compare categorical variables and an unpaired Student’s t-test or Mann-Whitney U test was used to compare numerical variables according to their normal distribution. The level of significance was set at an a priori two-tailed level of P
