Assessing blood culture contamination

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A Research Paper

Presented to the Graduate Faculty of the

Department of STEM Education and Professional Studies at

Old Dominion University
In Partial Fulfillment of the Requirements for the

Master of Science in Occupational and Technical Studies


Deborah Dawson Harris

August 2012


Deborah D. Harris completed this research project under the direction of Dr. John Ritz in SEPS 636, Problems in Occupational and Technical Studies. It was submitted to the Graduate Program Director as partial fulfillment of the requirements for the degree of Master of Science in Occupational and Technical Studies.

Approved By: _______________________________

Dr. John Ritz

Research Advisor and

Graduate Program Director

Occupational and Technical Studies

Old Dominion University

Date: ______________________


The author wishes to express a very special thank you to Dr. John Ritz for the assistance, guidance and patience in completing this study. His outstanding leadership and direction has been challenging yet very rewarding.

Gratitude is also extended to the clinical coordinator of the laboratory of the study hospital. Without her assistance and overwhelming support, this study would not have been possible.

























Table 1, Blood Culture Collection Survey Analysis…………………………………26

Table 2, Nursing Collections Data……………………………………………………27

Table 3, Phlebotomy Collections Data………………………………………………..28

Table 4, Comparison of Nursing and Phlebotomy Contamination Rates………….....29



The determination of bacteria actively growing in a patient’s bloodstream is a serious medical finding with life threatening implications. The collection of blood cultures to make this determination is a significant test in the clinical laboratory. Positive blood cultures are causes of considerable morbidity and mortality; such findings are alarming to clinicians and may warrant aggressive treatment regimes.

Blood cultures which become contaminated are false positive reactions and a major problem for microbiologists, clinicians and healthcare organizations. Such cultures are costly for healthcare institutions in several ways. Among the reasons are prolonged hospital stays and additional laboratory and radiologic testing. Patients may be treated with antimicrobial therapy which may, at a minimum, be inappropriate for their care. Additionally, the unnecessary prescribed therapy may have contraindications which could be detrimental to patients’ well being; many antimicrobial agents cause side effects in susceptible patients. Uncertainty over the interpretation of conflicting findings leads to increased consultations. Finally, the overuse of antimicrobials has been found to be a contributing factor in emerging antimicrobial resistance.

Laboratories often use dedicated phlebotomy teams to collect blood for laboratory tests, including blood cultures. Phlebotomists are trained in the proper technique for obtaining blood in a manner in which the normal microbes of the skin will not be introduced into the blood culture. Research has found that it is virtually impossible to have a contamination free rate (0%) in the modern clinical setting (Weinstein, 2003). Due to the significant impact on patient care and hospital costs, each laboratory is required to determine its monthly blood culture contamination rate. Actual rates vary between institutions, from as little as 0.65% to over 6% (Hall & Lyman, 2006). According to standards produced by the American Society of Microbiology, the rate of blood culture contamination should not exceed 3% (Ernst, 2004).

At the study hospital the blood culture contamination rates are inconsistently high. Despite numerous attempts to decrease the rate, the hospital seems unable to sustain an adequate contamination rate.


The problem of this study was to evaluate blood culture collection procedures utilized at the study hospital to determine the cause of the high contamination rates.


To provide a framework, answers to the following questions will guide this study:

RQ1: What are the recommendations of the College of American Pathologists?

RQ2 : Is there consistent protocol compliance for aseptic technique among personnel collecting blood for culture?

RQ3: Is the contamination rate significantly higher for nursing personnel than for phlebotomy?

RQ4: Does the study hospital provide collaboration and feedback to individuals and departments regarding contamination rates?


Blood cultures are widely accepted as an important tool to detect serious bloodstream infections, including endocarditis. Bacteremia or septicemia is among the most serious of clinical infections. Emerging pathogens for certain patient demographics has led to more sensitive methods to isolate and identify causative agents. One method of increasing the sensitivity of blood cultures is to enhance nutrients in the blood culture bottles in order to grow fastidious organisms. Although the ability to grow these organisms is advantageous, the downside is that the enhancements will also grow minute amounts of skin flora when present. Another reason for the increase in contamination is that newer, continuous monitoring blood culture systems have the ability to detect very small amounts of bacteria in the bottles. While increasing sensitivity for pathogens is favorable, the detection of contamination is confusing for the clinician. Contamination may occur during blood culture collection, during inoculation of media, while subculturing or from other events of processing specimens. Another reason given for the increase in contamination is due to the increased use of central venous access catheters. When these access lines are used to obtain blood for culture, studies have shown an increase in contamination (Weinstein, 2003).

Many of the organisms associated with contamination, or false positive reactions, may also be significant pathogens. This leads to difficult situations for physicians who are attempting to determine diagnostic and therapeutic strategies. Despite the fact that physicians are aware of the common agents of contamination, nearly half of patients with contaminated blood cultures are still treated with antibiotics (Robert, 2011).

The financial consequences of blood culture contamination have been described in several studies. A study conducted by Bates et al. compared the costs of charges of patients with contaminated blood cultures to patients with cultures which were true negatives. Individuals in both study groups had comparable health issues. The study found that contamination led to a 20% increase in laboratory charges and a 39% increase in intravenous antibiotic charges (Bates, Goldman & Lee, 1991). In a subsequent study of blood cultures shown to be contaminated with coagulase-negative staphylococci, almost half the patients were treated with antimicrobial therapy. The estimated cost of this unnecessary treatment was $100 per patient (Souvenir, 1998). More recent studies show that contaminated blood cultures can increase a patient’s hospital stay by as much as 4.5 days and add more than $5000 to the cost of treatment (Ernst, 2004). In 2004, another study found that the estimated expense of a single positive blood culture was $5506 per patient. Moreover, an institution that processes blood cultures on ten new patients per day could free up 82 bed-days and reduce expenses by $100,500 per year if the contamination rate is reduced by 0.5% (Berkeris, Twoerk, Walsh & Valenstein, 2005). A study was conducted at a 968-bed tertiary care hospital in Dallas, Texas, for a 13 month period from December 2006 to December 2007. Comparison of median patient charges between negative cultures and false positive episodes showed $8,720 in additional charges per contamination event. The researchers concluded that with contamination rates from 5.6% to 7.4%, the additional charges for evaluation of patients would range from $6.7 million to $8.9 million annually (Gander et al., 2009). Those with contaminated blood cultures have been found to incur a median cost of $874 for intravenous antibiotics, versus $492 for negative cultures. Total lab costs for contamination yielded a median of $2056 versus $1426 for negative findings (Robert, 2011). A study conducted primarily to determine the financial impact of contaminated blood cultures was performed over a 13 month period (July 2007 to July 2008). Conducted in Northern Ireland at a 426 bed teaching hospital, the research concluded that 254 bottles classified as contaminated added 1372 extra hospital days and incurred additional hospital costs of $1,905,572 per year (Alahmadi et al., 2011).

Additionally, contaminated blood cultures can affect patients’ quality of life. Prolonged hospital stays prevent patients from rejoining their families and their jobs. Lost wages and time spent away from family keeps patients from reclaiming their lives and is difficult to quantify (Ernst, 2004).

Another serious consequence of contamination is the administration of inappropriate antibiotic therapy. The misuse of antibiotics can not only lead to the emergence of organisms which are multi-resistant, but also increases the risk of Clostridium difficile infection (Thompson & Madeo, 2009).


The following limitations of this study are recognized by the researcher:

  1. The primary purpose of this study is to determine which, if any, of the known causes may have led to fluctuating contamination rates at the study hospital. There may be factors, yet to be described in the literature, which may also contribute. It is beyond the scope of this study to determine if there is an additional factor other than those currently identified to effect contamination rates.

  2. The research was conducted at the study hospital utilizing the standard operating procedures for blood culture collection at that facility. Varying procedures and demographics at other hospitals may result in substantially different results.

  3. It is beyond the scope of this study to implement changes. Findings will be presented to the infection prevention, phlebotomy and microbiology departments overseeing the study laboratory.


There were several assumptions in this study which the researcher assumed to true. The assumptions were as follows:

  1. Since aseptic site preparation is the most important factor in collecting uncontaminated blood cultures (Ernst, 2004), they must be collected in a manner in which to prevent contamination. Any healthcare worker collecting blood for this purpose should be knowledgeable about aseptic techniques. In addition to a specific procedure for site preparation, the bottle tops should be cleaned prior to introducing blood into them. If an intravenous access line is used, the “scrub the hub” technique is required (Department of Health and Human Services, 2010). It is essential that personnel have an understanding of the importance of compliance to protocol for collection. This study assumes that those collecting blood for cultures have been educated regarding basic aseptic techniques and its significance.

  2. Several commercial products are available for site preparation, and they are not all created equally. Each has differing contact times which should be strictly adhered to. This study is based on the assumption that those collecting blood for culture are aware of and adhere to the contact time requirement for the preparation used.

  3. Collection of blood for culture from intravenous lines is discouraged, yet it is still performed in practice (Ernst, 2004). Institution policy states that if a specimen is collected in this manner, it should be so noted. For the purpose of this study, it is assumed that all blood is collected peripherally unless otherwise noted.

  4. The volume of blood is crucial for culture. Volumes for adult blood cultures should not exceed 12 ml per bottle because overfilling can lead to false positive results (Ernst, 2004). Laboratory personnel are required to observe the bottles and make note of an improper fill. This study presumes that the bottles are properly filled unless otherwise noted.

  5. Finally, the order of tubes filled is very important. If a patient is having other blood work ordered simultaneously, the blood culture bottles should be filled first to avoid contamination (Ernst, 2004). This study assumes that this procedure is being followed by all personnel.
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