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date zone size (mm)
23-Jan-10 23
24-Jan-10 27
25-Jan-10 26
26-Jan-10 25
27-Jan-10 25
28-Jan-10 24
29-Jan-10 24
30-Jan-10 26
31-Jan-10 271-Feb-10 29
2-Feb-10 29
3-Feb-10 23
4-Feb-10 23
5-Feb-10 22
6-Feb-10 23
7-Feb-10 238-Feb-10 22
9-Feb-10 22
10-Feb-10 23
11-Feb-10 23
12-Feb-10 22
date zone size (mm)
1-Jan-10 25
2-Jan-10 243-Jan-10 25
4-Jan-10 24
5-Jan-10 26
6-Jan-10 24
7-Jan-10 27
8-Jan-10 25
9-Jan-10 2610-Jan-10 27
11-Jan-10 27
12-Jan-10 26
13-Jan-10 28
14-Jan-10 23
15-Jan-10 24
16-Jan-10 27
17-Jan-10 26
18-Jan-10 26
19-Jan-10 28
20-Jan-10 25
21-Jan-10 25
22-Jan-10 24
Quiz: anything unusual about
QC zone sizes? QC ATCC
25923 (Saureus) with
Cefoxitin disc
(FOX)
CLSI: zone size
within 22-29mm
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Quality Control and QualityAssurance for Antibiotic Testing
22 Sep 2010
Microbiology Technical Workshop
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Introduction
Various standards
eg CLSI, CDS
Various methods
Eg disc susceptibility, microbroth dilution Follow QC instructions as stated
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Introduction (2)
Some general principles apply:
1. Materials and Procedures : strictly adhere to2. Able to detect abnormalities and take
necessary corrective actions
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Materials & Procedures
General: Expiry date & storage
conditions manufacturersrecommendation
1. Media:
sterility
Support growth
Does not interfere with activity of antibiotics
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Materials & Procedures (3)
Perform and interpret correctly
Technologists : adequately trained
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Detect Errors / Corrective actions
Documentation
Useful for monitoring / troubleshooting futureQC failures
CAP requirements
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What to do when QC is out
CLSI recommendations:
ID cause
Cause found repeat x 01
Repeat ok = case close
Repeat out of range repeat
No obvious
cause
5 consecutive days
All within range= case close
1 out ofrange
Re-examine
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Common sources of error
Media Storage
Thickness
Contamination
pH
Wrong media
Antibiotics
Storage Wrong disc
QC strains Wrong strains
Inoculum
Storage
Contamination
Old cultures
Procedures
Incubation conditions Disc placement
transcription
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Other Tools
Control charts and Westgard rules
CUSUM
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date zone size (mm)
b
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Control Chart ATCC 25923 SAU with FOX
20
21
22
23
24
25
26
27
28
29
30
1-Ja
n-1
0
3-Ja
n-1
0
5-Ja
n-1
0
7-Ja
n-1
0
9-Ja
n-1
0
11-Jan-1
0
13-Jan-1
0
15-Jan-1
0
17-Jan-1
0
19-Jan-1
0
21-Jan-1
0
23-Jan-1
0
25-Jan-1
0
27-Jan-1
0
29-Jan-1
0
31-Jan-1
0
2-Feb-1
0
4-Feb-1
0
6-Feb-1
0
8-Feb-1
0
10-Feb-1
0
12-Feb-1
0
date
1-Feb-10 29
2-Feb-10 29
3-Feb-10 23
4-Feb-10 23
5-Feb-10 22
6-Feb-10 23
7-Feb-10 238-Feb-10 22
9-Feb-10 22
10-Feb-10 23
11-Feb-10 23
12-Feb-10 22
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Warning rules
Warning 11112SD2SD2SD2SD : It is violated if the IQC value exceeds the
mean by 2SD. It is an event likely to occur normally in less
than 5% of cases.
Warning 22222SD2SD2SD2SD : It detects systematic errors and is violatedwhen two consecutive IQC values exceed the mean on the
same side of the mean by 2SD.
Warning 44441SD1SD1SD1SD : It is violated if four consecutive IQC valuesexceed the same limit (mean 1SD) and this may indicate the
need to perform instrument maintenance or reagent
calibration.
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Mandatory rules
Mandatory 11113SD3SD3SD3SD : It is violated when the IQC value exceeds
the mean by 3SD. The assay run is regarded as out of
control.
Mandatory RRRR4SD4SD4SD4SD : It is only applied when the IQC is tested induplicate. This rule is violated when the difference in SD
between the duplicates exceeds 4SD.
Mandatory 10x10x10x10x : This rule is violated when the last 10consecutive IQC values are on the same side of the mean or
target value.
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Scenario 1
New lot / new antibiotics
How frequently should you QC?
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Scenario 2
Check
Media Antibiotics
QC organism Procedure
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Scenario 1
New antibiotic introduced
CLSI Test for 30 consecutive days
If no more 3 (out of 30) are outsideacceptable range - convert to weekly testing
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Scenario 2
7 Oct 2009 - QC ATM 20mm (expected
23-29mm) What would you do?
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Scenario 2
Repeat testing performed by same staff
Correct QC organism, media, procedure,incubation, interpretation
Wrong inoculum - too heavy
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Scenario 3
14 Oct 2008
Vitek Gram positive panel QC Multiple drugs MIC - resistant
Expected - sensitive
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Scenario 3
Purity plate - contaminated with other
organisms
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Scenario 4
QC Vitek Gram positive panel
Multiple antibiotics - resistant Expected - sensitive
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Scenario 4
Test repeated
With organism from purity plate (prev run)- resistant
And separate set from weekly QC plate -sensitive
Wrong ATCC used.
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Quality assurance
Education
External Proficiency test, eg CAP Literature and publications
Accreditation