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ORIGINAL ARTICLE
Year : 2014  |  Volume : 55  |  Issue : 3  |  Page : 201-203  

Quality assurance in blood culture: A retrospective study of blood culture contamination rate in a tertiary hospital in Nigeria


Department of Medical Microbiology and Parasitology, National Hospital Abuja, Abuja, Nigeria

Date of Web Publication7-May-2014

Correspondence Address:
Iregbu Iregbu Chukwuemeka
Department of Medical Microbiology and Parasitology, National Hospital, Plot 132, Central Business District (Phase II), PMB 425, Garki, Abuja - 900 001
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0300-1652.132038

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   Abstract 

Background: Blood culture is a critical tool for diagnosing septicaemia. Quite frequently, contamination of blood sample poses a great challenge to accurate diagnosis. This study evaluated the rate of blood culture contamination in our hospital over a one-year period. Materials and Methods: It was a retrospective study of 1032 blood cultures carried out in a clinical laboratory of a tertiary hospital in North Central part of Nigeria between 2010 and 2011. Results: There were 730 blood cultures from paediatric and 302 adult patients. The overall yield was 22%; 107 out of the 730 were contaminated giving a contamination rate of 10.4%. Contamination rate was higher in children than in adult (11% vs 8%) specimen. These rates were much higher than the acceptable benchmark of 2-3%. The main contaminants were coagulase negative Staphylococcus, Bacillus species, Diphtheroids and Enterococcus species. Conclusion: Contamination rate is high, and mainly due to normal skin flora, suggesting aseptic collection challenges as the main cause. We recommend a review of the entire process of blood collection for culture and analysis with a view to instituting appropriate quality assurance measures to reduce the contamination rate.

Keywords: Blood culture, contamination, quality assurance


How to cite this article:
Chukwuemeka II, Samuel Y. Quality assurance in blood culture: A retrospective study of blood culture contamination rate in a tertiary hospital in Nigeria. Niger Med J 2014;55:201-3

How to cite this URL:
Chukwuemeka II, Samuel Y. Quality assurance in blood culture: A retrospective study of blood culture contamination rate in a tertiary hospital in Nigeria. Niger Med J [serial online] 2014 [cited 2019 Nov 15];55:201-3. Available from: http://www.nigeriamedj.com/text.asp?2014/55/3/201/132038


   Introduction Top


Blood culture is a very important life-saving investigation in patients with sepsis and bloodstream infections. [1] The aim of culture is to isolate pathogen and select appropriate antibiotic agents for an effective therapy based on in vitro sensitivity of the pathogens against a range of antibiotics. [2],[3],[4] A false positive blood culture tends to limit the utility of this important investigative tool with associated negative patient outcomes. Blood culture contamination rate is a commonly used quality indicator in blood culture processing.

One of the major challenges in blood culture is contamination, which occurs mainly from the resident skin flora of the patient, and poses serious challenges to both clinicians and laboratory staff. [1],[5],[6] A potential bacterial contaminant is defined as bacteria that commonly inhabit human skin, and when grown in culture represents contamination in more than 50% of the time. [7] Contamination due to skin flora especially in a solitary culture, makes interpretation difficult, and may result in excessive and sometimes unnecessary use of antibiotics with the risk of promoting bacterial resistance, increased morbidity and mortality, extended hospital stay and increased cost. [8]

The acceptable blood contamination rate benchmark is 2-3%, [7],[9],[10],[11],[12] with rates ranging from 1% to 9%. [13] Factors associated with blood culture contamination include, but are not limited to, poor technique and procedure used to collect blood, lack of dedicated phlebotomists, [8],[9],[14] improper skin antisepsis. [15],[16],[17] This study determined the contamination rate of blood culture in our facility within a one year period.


   Materials and methods Top


This was an one-year retrospective study of all blood cultures carried out between July 2010 and June 2011 at the Medical Microbiology Laboratory of the National Hospital, Abuja (NHA) Nigeria. Initially, solitary blood cultures were carried out using the oxoid signal culture bottle (Oxoid Ltd., Basingstroke, UK) or the Bactec culture bottle (Becton Dickinson). Later on, blood culture for adults was by the use of two or three bottles of Bactec in a single set aiming at culturing between 20-24 ml of blood, whereas the solitary cultures for paediatrics continued. The third bottle was often added where either anaerobic or fungal infection was suspected. All culture bottles were incubated at 35-36 o C at atmospheric pressure for a maximum duration of seven days. Cultures indicating growth were sub-cultured for isolation and subsequent identification. Records of all the blood cultures were reviewed, and the data were analysed for age and gender of the patients, type of cultures (solitary or multiple), total number of culture and the growths, and the type of culture systems used. We also sought information from clinicians on the techniques of collection and the type of antiseptic often used. Number of cultures was based on number of patients and not on number of culture bottles or set. Interpretation of results was based on the following criteria:

Growth of a known skin flora in a solitary culture - Contaminant

Growth of a known skin flora in more than one bottle in a multiple culture - Pathogen

Growth of a known pathogen in a solitary or multiple cultures - Pathogen


   Results Top


A total of 1032 blood cultures were carried out during the period; of which, 730 (70.7%) were blood specimens from paediatric group while 302 (29.1%) were from adults. There were 620 (60%) males and 412 (40%) females, in total [Table 1].
Table 1: Age category and gender of patients

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The total yield was 226 (22%), out of which 107 (47%) were contaminants while 119 (53%) were pathogens [Table 2]. The overall contamination rate was 10.4%; while it was 11% in paediatrics and 8% in adults. Every 16 adult and 7 paediatric cultures yielded a pathogen while every 13 adult and 9 paediatric cultures yielded a contaminant.
Table 2: Age category and blood culture yield

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The four most common contaminants were coagulase negative Staphylococus (CoNS) (55%), Enterococcus faecalis (16%), Bacillus Spp (8%), and Diphtheroids (6%) [Table 3]. S. aureus (56%) and and Klebsiella pneumoniae (13%) were the predominant pathogens [Table 4].
Table 3: Profile of contaminants isolated from different age categories

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Table 4: Profile of pathogens isolated from different age categories

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   Discussion Top


The results of this study revealed that there were more males than females, and more paediatric patients than adults investigated for bloodstream infection. Although the reason for the preponderance of paediatric patients was not quite clear, one reason could be due to the fact that clinical history and elicitation of signs are much easier in adults than in paediatric patients, thus helping internal medicine clinicians to be more objective in making a clinical impression of sepsis in adults than likely in paediatrics; and therefore, make less blood culture requests. However, the total number of cultures per pathogen yield was more in adults than paeditrics suggesting that paediatricians were more exact in their clinical impressions than the internal physicians. This seeming contradiction may be due to ingestion of antibiotics prior to blood sample collection, a situation that lowers the true positive rate in the adult population in an environment of inappropriate antibiotics use like ours.

The total blood culture contamination rate in National Hospital Abuja was found to be 10.4%, far above the benchmark of 2-3%. [7],[9],[10],[11],[12] Contamination was relatively more in paediatric patients than in adults, with a total culture per contaminant yield of 9 against 13, and rate of 11% against 8%. Most likely, factors responsible for this high rate include, but are not limited to, poor techniques, the use of non-dedicated phlebotomists and variable types of skin antiseptics, which, unfortunately, do not include iodine or iodophore. Difficulty in collecting blood from paediatric patients also account for the higher contamination rate. A previous study has shown that contamination rate can be significantly reduced through, among others, scrupulous attention to aseptic skin cleansing and improved venipuncture technique, using isopropyl alcohol and a tincture of iodine. [18] The use of dedicated phlebotomists has also been found to have similar improvement effect. [8]

Coagulase negative Staphylococcus (CoNS) was found to be the predominant contaminant in this study, similar to studies elsewhere. [9],[19],[20] This does not suggest that all CoNS grown in blood culture are contaminants. It has been found to cause 12.4% of clinically significant isolates from blood culture, and the third most common cause of bacteraemia because of their high prevalence, especially in patients with prosthetics and central venous catheters. [15],[21],[22] Staphylococcus aureus and K. pneumoniae were the most common pathogens isolated. This agrees with the results of earlier studies where these same organisms have been identified as the most common causes of bloodstream infections. [23],[24],[25]

In conclusion, rates of blood culture contamination in the National Hospital Abuja are high. There is an urgent need to institute established preventive measures to reduce the rates. This will go a long way in mitigating all the adverse consequences of blood culture contaminations such as increased cost of care, increased morbidity and mortality rates. A prospective study will be necessary to identify the main factors responsible for the contaminations and to evaluate the impact of interventions.

 
   References Top

1.Hall KK, Lyman JA. Updated review of blood culture contamination. Clin Microbiol Rev 2006;19:788-802.  Back to cited text no. 1
    
2.Bryan CS. Clinical implications of positive blood cultures. Clin Microbiol Rev 1989;2:329-53.  Back to cited text no. 2
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3.Kenyon CR, Fatti G, Schrueder N, Bonorchis K, Meintjes G. The value of blood culture audits at peripheral hospitals. S Afr Med J 2012;102:224-5.  Back to cited text no. 3
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4.Pasqualini L, Mencacci A, Leli C, Montagna P, Cardaccia A, Cenci E, et al. Diagnostic performance of a multiple real-time PCR assay in patients with suspected sepsis hospitalized in an internal medicine ward. J Clin Microbiol 2012;50:1285-8.  Back to cited text no. 4
    
5.Youssef D, Shams W, Bailey B, O'Neil TJ, Al-Abbadi MA. Effective strategy for decreasing blood culture contamination rates: The experience of a Veterans Affairs Medical Centre. J Hosp Infect 2012;81:288-91.  Back to cited text no. 5
    
6.Willems E, Smismans A, Cartuyvels R, Coppens G, Van Vaerenbergh K, Van den Abeele AM, et al. Bilulu Study Group. The preanalytical optimization of blood cultures: A review and the clinical importance of benchmarking in 5 Belgian hospitals. Diagn Microbiol Infect Dis 2012;73:1-8.  Back to cited text no. 6
    
7.Talbot TR, Ashburn R, Storrow AB, Speroff T, Dittus RS, Self WH, et al. A quality improvement programme to reduce blood culture contamination in the emergency department. Presented at the 21 st Annual Scientific Meeting of the Society for Healthcare Epidemiology of America. Dallas Texas; 2011.  Back to cited text no. 7
    
8.Bekeris LG, Tworek JA, Walsh MK, Valenstein PN. Trends in blood culture contamination: A College of American Pathologists Q-Tracks study of 356 institutions. Arch Pathol Lab Med 2005;129:1222-5.  Back to cited text no. 8
    
9.Schifman RB, Strand CL, Meier FA, Howanitz PJ. Blood culture contamination: A College of American Pathologists Q-Probes study involving 640 institutions and 497134 specimens from adult patients. Arch Pathol Lab Med 1998;122:216-21.  Back to cited text no. 9
    
10.Reller LB, Murray PR, MacLowry JO. Cumitech 1A, Blood Cultures II. In: Washington JA, coordinating ed. American Society for Microbiology, Washington DC; 1982.  Back to cited text no. 10
    
11.Strand CL, Wajsbort RR, Sturmann K. Effect of iodophor vs iodine tincture skin preparation on blood culture contamination rate. JAMA 1993;269:1004-6.  Back to cited text no. 11
    
12.Weinbaun FI, Lavu S, Danek M, Sixsmith D, Heinrich GF, Mills SS. Doing it right the first time: Quality improvement and the contaminant blood culture. J Clin Microbiol 1997:35:563-5.  Back to cited text no. 12
    
13.Murillo TA, Beavers-May TK, English D, Plummer V, Stovall SH. Reducing contamination of peripheral blood cultures in a pediatric emergency department. Pediatr Emerg Care 2011;27:918-21.  Back to cited text no. 13
    
14.Spitalnic SJ, Woolard RH, Mermel LA. The significance of changing needles when incoculating blood cultures: A meta-analysis. Clin Infect Dis 1995;21:1103-6.  Back to cited text no. 14
    
15.Chandraseker PH, Brown WJ. Clinical issues of blood cultures. Arch Intern Med 1994;154:841-9.  Back to cited text no. 15
    
16.Mylotte JM, Tayara A. Blood cultures: Clinical aspects and controversies. Eur J Clin Microbiol Infect Dis 2000;19:157-63.  Back to cited text no. 16
    
17.Washington JA 2nd, Ilstrup DM. Blood cultures: Issues and controversies. Rev Infect Dis 1986;8:792-802.  Back to cited text no. 17
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18.Archibald LK, Pallangyo K, Kazembe P, Reller LB. Blood culture contamination in Tanzania, Malawi and the United States: A microbiological tale of three cities. J Clin Microbiol 2006;44:4425-9.  Back to cited text no. 18
    
19.Calfee DP, Farr BM. Comparison of four antiseptic preparations for skin in the prevention of contamination of percutaneously drawn blood cultures: A randomized trial. J Clin Microbiol 2002;40:1660-5.  Back to cited text no. 19
    
20.Novis DA, Dale JC, Schifman RB, Ruby SG, Walsh MK. Solitary blood cultures: A College of American Pathologists Q-probes study of 132,778 blood culture sets in 333 small hospitals. Arch Pathol Lab Med 2001;125:1290-4.  Back to cited text no. 20
    
21.Weinstein MP, Towns ML, Quartey SM, Mirrett S, Reimer LG, Parmigiani G, et al. The clinical significance of positive blood cultures in the 1990s: A prospective comprehensive evaluation of the microbiology, epidemiology, and outcome of bacteremia and fungemia in adults. Clin Infect Dis 1997;24:584-602.  Back to cited text no. 21
    
22.Rubin LG, Sanchez PJ, Siegel J, Levine G, Saiman L, Jarvis WR, Pediatric Prevention Network. Evaluation and treatment of neonates with suspected late-onset sepsis: A survey of neonatalogists' practices. Pediatrics 2002;110:e42.  Back to cited text no. 22
    
23.Meremikwu MM, Nwachukwu CE, Asuquo AE, Okebe JU, Utsal SJ. Bacterial isolates from blood cultures of children with suspected septicaemia in Calabar, Nigeria. BMC Infect Dis 2005;5:110.  Back to cited text no. 23
    
24.Prabhu K, Bhat S, Rao S. Bacteriologic profile and antibiogram of blood culture isolates in a padiatric care unit. J Lab Physicians 2010;2:85-8.  Back to cited text no. 24
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25.Iregbu KC, Elegba OY, Babaniyi IB. bacteriological profile of neonatal septicaemia in a tertiary hospital in Nigeria. Afr Health Sci 2006;6:151-4.  Back to cited text no. 25
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]


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