Blood Products Advisory Committee Meeting

December 12, 2002

# 

# Issue Summary: (1 of 3 for the BPAC Bacterial contamination topic) 

# Quality Control (QC) Measures for Aseptic Collection and Processing of Platelets and Platelets Pheresis

Background:

Although blood collection and processing procedures are intended to
produce non-infectious blood components, bacterial contamination still
may occur. Surveillance studies have found rates of contamination as
high as 0.4% in single donor platelets, although rates at or below 0.2%
are more reported. The causes include occult bacteremia in the donor,
inadequate or contaminated skin preparation at the phlebotomy site,
coring of a skin plug by the phlebotomy needle, and breaches of the
closed system from equipment defects or mishandling. Platelet products
are more likely than other labile components to be associated with
sepsis due to their storage at room temperature, which is permissive of
bacterial growth. For the same reason, bacterial cultures of platelets
provide the best indication of the rate of contamination, provided that
the sample for culture is obtained on a suitable sample volume and at a
suitable time post-collection.

A variety of procedures may be used to obtain a valid platelet sample
for bacterial culture. Aseptic techniques are required in order to
minimize the risk of false positive cultures due to contamination at the
time of sampling or upon inoculation in culture. Additionally, it is
prudent to retain a sample that can be used for repeat culture to
validate a positive result. Large volume samples removed from a several
unit platelet pool or single donor apheresis unit can be cultured any
time post-collection. However small volume samples (e.g. 2-5 ml removed
from a single whole blood unit) should be obtained only after a 24-48
hour delay post-collection. The delayed sampling of a small volume
permits bacterial growth to a level that subsequent assays will reliably
detect, thereby overcoming sampling errors at low contamination levels.

# 

# High-Throughput Sampling Using a Sterile Connecting Device (SCD) 

Sampling solely for quality control purposes can be accomplished by an
aseptic, but open method (e.g. needle aspiration) for units at the time
of issue (i.e. for use within four hours) or on outdating units.
Conversely, sampling of platelets for the purpose of establishing a
criterion for issuance of platelets as \"culture negative to date\"
based on a negative result of bacterial cultures requires that the
integrity of the closed system should be maintained. This is because
platelets may continue to be stored for a variable period after sampling
and before use. Suitable methods of sampling in this case would include
the use of integral satellite containers, or stripping, refilling, and
then pinching off duplicate pigtails. Sampling also may be done into
collection containers via the use of sterile connecting devices.

The FDA Guidance for Industry (Use of Sterile Connecting Devices in
Blood Bank Practice, November, 2000) (1) describes an SCD as a
functionally closed system for component preparation. However, given the
room temperature storage of platelet preparations, current regulations
do not permit extension of the 4 hour outdate for pooled random donor
platelets pending submission of supporting data to ensure that sterility
is not compromised by multiple SCD connections. While published US data
support the sterility of SCD procedures when combined with visual
inspection of the welded joint(2,3), a single European study described a
1.4% product contamination rate when an SCD was used to obtain samples
for culture (4).

Recent clearance of two semi-automated culture systems for QC of
platelet components has generated momentum within industry to culture
in-date apheresis products followed by either product quarantine for a
defined culture interval, or recall of a culture-positive distributed
product. In part due to the absence of published data supporting SCD for
sampling from in-date products, FDA has previously taken the position
that the cleared culture systems should carry special labeling
[prohibiting]{.underline} their use as pre-release screening tests, due
to a) possible risk of increased extrinsic contamination from SCD
sampling and b) absence of data for the cleared devices when used for
pre-release testing c) concern about off-label use of platelets older
than the current 5 day shelf life (5). Similar concerns regarding
extrinsic contamination may also exist if SCD procedures are used to
collect a culture sample from many (or all) platelet products prior to
release for transfusion. The Committee will hear a summary of available
data on this issue.

# Quality Control Strategies

The goal of quality control testing for bacterial contamination should
be to assure that blood collection and processing procedures conform to
defined standards. Statistically-based sampling of platelets for culture
(or analogous testing) by a validated method will provide a reliable
indication of the rate of contamination for all the labile products.
However, the number of samples tested must be very large. (For example,
based on Poisson statistics, it would require 0 failures out of 750
samples to be 95% confident that the contamination rate did not exceed
0.4%.) For very large blood collection centers, sampling on this order
of magnitude may be possible by culturing platelets only at outdate.
Conversely, small centers should consider testing of all units older
than 24-48 hours by a process of sterile sampling at the time of issue
or outdate. Daily (or, if frozen, weekly) samples can be pooled to
reduce the number of cultures. Individual samples contributing to
positive pools should be retested singly to determine the identity of
the contaminated units, thereby permitting a prompt investigation of
potential correctable causes. Correlations with common causal factors
such as operator errors, shift, reagent batch, or procedure should be
considered. Retained duplicate samples should be used to confirm or
reevaluate the initial bacteriological findings.

The following will be presented by FDA for consideration as a minimal
quality control program for all platelet products collected at blood
centers.

a)  As a quality control for aseptic collection and processing of labile
    components, blood collection centers should determine the rate of
    bacterial contamination in platelets at least yearly by culturing
    1,500 or more units (about 30 units per week or 5% of units released
    after 24 hours of storage, whichever is larger.) Standard
    statistical methods should be used to identify significant
    deviations from a baseline contamination rate not to exceed 0.2%.
    The chosen method should be based on a predetermined level of
    confidence to exclude a maximum tolerated rate of contamination, and
    an action limit should be established.

b)  All instances of a positive culture should be investigated promptly
    to facilitate identification of a correctable cause.

c)  Whenever the observed rate of bacterial contamination exceeds the
    defined action limit, a comprehensive investigation into potential
    causes of contamination should be undertaken and all collection and
    processing procedures should be revalidated.

*[Example:]{.underline}*

*A blood center wishes to establish surveillance to detect bacterial
contamination rates significantly in excess of 0.2%. The following chart
is derived from binomial statistics:*

*Candidate*

*Action Limit Confidence in Power to detect actual contamination rate @*

*[#(+)/# sampled]{.underline} [Positive Result]{.underline}
[0.4%]{.underline} [0.6%]{.underline} [0.8%]{.underline}
[1.0%]{.underline}*

*[\>]{.underline}3 per 400 95.3% 22% 43% 62% 76%*

*[\>]{.underline}5 per 800 97.6% 22% 52% 77% 90%*

*[\>]{.underline}7 per 1600 95.5% 46% 84% 97% 99.6%*

*The blood center collects 12 units of platelets per day, five days per
week. Cultures of units released after 48 hours, plus outdated units,
number 30 units per week that are processed as 6 weekly cultures of five
unit pools. An action limit is set to revalidate the collection
procedures if the observed contamination rate exceeds 0.42% for yearly
samples of 1,560 units. The action limit was established based on an
expected contamination rate of 0.2%, a sample size of 1,560, and a
cut-off determined as baseline plus 2-sigma variation. For this scheme,
the likelihood of rejecting a conforming process is 4.5% (once every 22
years). The confidence levels (i.e. power) to exclude actual
contamination rates of 1%, 0.8% and 0.6% are 99.6%, 97% and 84%
respectively.*

*Over a one-year period, 7 positive platelet pools are identified,
traceable to 7 individual units. The individual cases were investigated,
but no attributable cause was identified. The observed contamination
rate of 7/1,560=0.45% exceeds the action level. Confidence that the
actual contamination rate exceeds 0.2% is greater than 95%. An intensive
review is conducted, and all collection and processing procedures are
revalidated.*

Questions for the BPAC:

> **Do available data on the sterility of the sterile connecting device
> procedure support the use of this procedure to collect samples for
> bacterial detection from in-date platelet products?**

**Does the Committee concur with FDA's proposed statistical approach to
providing quality control for platelet contamination?**

References:

1.  FDA Guidance for Industry (Use of Sterile Connecting Devices in
    Blood Bank Practice, November, 2000)

2.  AuBuchon JP, Pickard C, Herschel L Sterility of plastic tubing welds
    in components stored at room temperature Transfusion 1995
    35:303-307.

3.  AuBuchon et al. Experience with universal bacterial culturing to
    detect contamination of apheresis platelet units in a hospital
    transfusion service. Transfusion 2002; 42, 855-861.

4.  Mertens G, Muylle L, Goossens H. Possible implication of sterile
    connecting device in contamination of pooled platelet concentrates.
    Trans Sci 1997, 18(3),387-392

5.  Wagner SJ, Moroff G, Katz AJ, Friedman LI, Comparison of bacteria
    growth in single and pooled platelet concentrates after deliberate
    inoculation and storage. Transfusion 1995; 35; 298-302.