Detection of Bacterial Contamination in Platelet Components
Vol. 6, No. 4, DECEMBER 2003
Bacterial contamination of platelets represents the
most frequent transfusion-associated infectious risk.
contamination levels of as few as 102 to 103 CFU/mL have been
associated with fever and positive blood cultures.
The incidence of clinically significant platelet-associated
contamination is estimated at 1/15,000 and death due to sepsis or
endotoxemia at 1/60,000 platelet transfusions.
New measures to limit and detect bacterial contamination in platelet
components to be implemented by March 2004 are expected to
significantly decrease current risks.
Extensive donor selection and testing strategies effectively reduce the
transmission of viral agents by asymptomatic volunteer blood donors. Today, the
most frequent transfusion-associated infectious risk in the United States is
sepsis associated with bacterial contamination of platelet components.
the frequency, clinical significance, and potential for fatal complications that
the presence of bacteria poses for certain patients, two accrediting agencies
(the American Association of Blood Banks and the College of American
Pathologists) have issued directives requiring the use of methods to detect and
limit bacterial contamination of platelets.
While bacterial contamination may affect any blood component, the
ambient storage temperature conditions for platelets make them most likely to
facilitate bacterial growth. Bacterial contamination of platelets can be found
in about 1 in 1,000 to 1 in 3,000 units (depending on the source of the
component and the methodology used to detect contamination). Bacteria, and/or
the endotoxins they produce, are introduced into the circulation in amounts
sufficient to cause sepsis or endotoxic shock. Estimates of the incidence of
clinically significant complications related to this problem remain imprecise,
due to the variability in case definition, protocols to evaluate transfusion
reactions, and the methods used to detect bacteria in blood components.
addition, many instances of clinically significant platelet bacterial
contamination are neither recognized, nor reported. In a multi-center study
coordinated by the US Centers for Disease Control and Prevention (CDC) designed
to identify and confirm bacterial contamination in transfused blood components
(the “BaCon Study”), the incidence of clinically significant platelet associated
contamination was estimated at 1/100,000 and death at 1/500,000 platelet
However, the report’s authors acknowledged that the strict
inclusion criteria for the study and the voluntary manner of reporting likely
resulted in substantially underestimating the incidence of this problem. In
addition, some contaminated
infusions go unrecognized because the patients are receiving antibiotic therapy
for their underlying condition. Other investigators have estimated that 1 in
2,500 to 11,400 whole blood derived platelet pools and 1 in 15,400 apheresis
platelet transfusions result in a clinically significant reaction.2,3
Although the concentration of
bacteria required to cause clinically significant reactions varies depending on
the microorganism, endotoxin production, clinical condition of the recipient,
and other factors, it is known that as few as 102 to 103
CFU/mL have been associated with fever and positive blood cultures.4
Contamination. Inoculation of bacteria in the blood collection set
may result from donor bacteremia or the skin surface during phlebotomy
procedure. The latter is believed to be the most common source, since the
majority of the isolates are microorganisms found on the skin and in dermal
appendages. The deeper epidermal layers, hair follicles, and sebaceous glands
harbor bacteria that are difficult to remove, even after thorough mechanical and
antiseptic arm preparation.
Although skin flora are the
most common bacteria, blood collection from asymptomatic, transiently bacteremic
donors is involved in a disproportionate share of cases of septic deaths
associated with platelet transfusions. Lethal outcomes result from both
bacterial growth and endotoxin production during storage. Most of the donor
bacteremias involve Gram negative microorganisms.
aseptic technique during phlebotomy is the first line of defense in preventing
bacterial contamination of blood components. The use of skin disinfectant
solutions that provide maximum bactericidal effect (e.g., iodophors or
chlorhexidine) is recommended,5 but recognized as only one measure in
the prevention of bacterial entry into the blood unit. A promising intervention
consists of the diversion of the initial aliquot of donor blood into an
integrally connected pouch. This reduces the possibility that a skin plug or
core cut with the needle during phlebotomy, harboring bacteria, will contaminate
the collection bag. Blood in the diversion pouch can be used for
immunohematologic and viral marker testing, without increasing blood loss
associated with donation. Laboratory and actual experience in European centers indicate that this change
in blood collection technique [diversion pouch] may reduce bacterial
contamination rates in blood components overall by about 40%, with the highest
reduction observed for common skin contaminants of the Staphilococcus
Detection of bacterial
contamination prior to transfusion, even if costly, would be a significant step
towards the elimination of transfusion-associated sepsis. The ideal
characteristics of a bacterial detection method are that it be simple,
practical, rapid, sensitive, specific, and inexpensive.
At this point, two
culture-based methods for bacterial detection have been licensed by the Food and
Drug Administration (FDA) to test platelet components “for quality control
purposes.” (FDA requires additional data to permit use of these devices for
“donor screening,” which implies an additional safety claim.) One of the quality
control devices, intended for use with leukoreduced platelets collected by
apheresis only, detects bacterial growth by sensing CO2 production.
The second method relies on oxygen consumption for the detection of bacterial
growth, and has been approved for both platelets from whole blood and apheresis.
Oxygen consumption measurement limits detection to aerobic microorganisms;
however, anaerobes rarely are implicated in clinically significant bacterial
contamination of platelets.
Typically, samples from
platelet units are obtained after an initial “lag phase” of at least 24 hours to
allow growth of the initial contaminating inoculum. Units then may be released
for distribution immediately after inoculation of samples into the growth
detection system, or after a set pre-release incubation time. Using this
approach to prevent product shortages introduces the likelihood that a small
number of units issued for distribution and transfusion will subsequently prove
positive for bacterial contamination. These events will occur for one of two
The inoculation of samples may have introduced bacteria into the
culture system that are not present in the distributed blood component (i.e.,
a “false positive” result—an event reported to occur in 1 in 500 to 1 in
5,000 inoculations, depending on technique and equipment used.)
The contamination is real (a “true positive”) but the bacteria are slow growing
strains, or present in very small numbers, taking several days to achieve
detectable titers. Preliminary data from those currently screening platelet
concentrates suggests that true positives tend to show up earlier than false
Algorithms for identifying bacterial growth in an already-transfused blood
component are being developed by hospitals and blood centers. Presumably, this
additional information about the organism and its antibiotic susceptibility will
assist in managing the transfusion recipient if clinical signs of infection have
Bacterial detection in whole
blood derived platelets remains a challenge at this time. Because multiple units
must be sampled per transfusion dose, sampling techniques, component management
logistics, and cost are barriers to culture-based assays. A number of
non-culture based methods have been proposed to detect contamination prior to
release: staining (Gram, Wright, or acridine orange) with microscopic
examination,4 chemistry assays (glucose, pH) using urine dipsticks,7and
inspection for a peculiar light diffraction phenomenon called “swirling.” These
methods are limited in their sensitivity and specificity, but are acceptable
alternatives to meet accreditation requirements (with the exception of
“swirling,” which is considered a secondary detection measure that requires
trained and proficient staff).
Apheresis platelets may not
be in sufficient supply or may not be the component of choice, so a gap between
the safety profile of bacterially-screened apheresis platelets and bacterially
unscreened whole blood derived platelets appears unavoidable until more
sensitive methods applicable to platelets from whole blood are available.
Alternative techniques are under development to bridge that gap.
Bacterial contamination of
platelets remains the most frequent infectious risk associated with transfusion.
Improved phlebotomy techniques and diversion devices will help reduce the
inoculation of skin flora into blood components. Detection of bacteria by
culture-based assays of platelets collected by apheresis should allow
interdiction of contaminated units prior to transfusion or, in some cases, early
management of clinically significant complications arising from the infusion of
bacteria during transfusion. Challenges for detecting contaminated whole blood
derived platelets remain.8 In the near term, quarantining for 24
hours prior to obtaining platelet aliquots for bacterial testing in practice
reduces platelet shelf life to 4 days instead of 5. If proposed studies
demonstrate that the techniques under discussion interdict bacterially
contaminated platelets, platelet storage could be increased to 7 days. Taken as
a whole, these steps add a margin of safety to current transfusion practices.
Kuchnert MJ et al.
Transfusion-transmitted bacterial infection in the United States, 1998 through
2000. Transfusion 2001;41:1493-9.
Ness P et al.
Single-donor platelets reduce the risk of septic platelet transfusion
reactions. Transfusion 2001;41:857-61.
Kleinman S et al.
Risks associated with transfusion of cellular blood components in Canada.
Transfus Med Rev 2003;17:120-62.
Yomtovian R, Jacobs
MR. Gram Stain and Culture Surveillance–Significant Findings and Clinical
Implications. Food and Drug Administration, Workshop on Bacterial Contamination
of Platelets, September 24, 1999. Available on line at:
Lee CK et al.
Impact of donor arm skin disinfection on the bacterial contamination rate of
platelet concentrates. Vox Sang 2002;83:204-208.
De Korte D et al.
Diversion of first blood volume results in a reduction of bacterial
contamination for whole-blood collection. Vox Sang 2002;83:13-16.
Werch JB et al.
Detecting bacteria in platelet concentrates by use of reagent strips.
- Pietersz RNI et al.
Detection of bacterial contamination of platelet concentrates. International
Forum. Vox Sang 2003:85:224-39.
Blood Bulletin is issued
periodically by America’s Blood Centers. Editor: Jay E. Menitove, M.D. The
opinions expressed herein are opinions only and should not be construed as
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Copyright America’s Blood Centers, 2003.
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©2003, Institute For Transfusion
Editor: Donald L. Kelley, M.D., MBA: