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ผลการประชุม ISO/TC 34/SC 9 WG 4. ISO Guide 43 Microbiology of food and animal feeding stuffs – Specific requirements and guidance for proficiency testing by interlaboratory comparison. Background. ISO Guide 43—Microbiology of food and animal feeding stuffs –

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ผลการประชุมISO/TC 34/SC 9 WG 4

ISO Guide 43

Microbiology of food and animal feeding stuffs – Specific requirements and guidance for proficiency testing by interlaboratory comparison


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Background

ISO Guide 43—Microbiology of food and animal feeding stuffs –

(WD 22117) Specific requirements and guidance for proficiency testing

by interlaboratory comparison

  • Developed (initial work) under direct responsibility of

  • ISO Technical Committee 34 (TC 34/SC 9)—Food products : Microbiology

  • The further development of this standard was done by

  • Working Group 4: Proficiency testing

  • Mirror committee—TC 957 : Microbiology of food and agricultural

  • products

  • Thai experts in WG4 : Mrs.Pensri Rodma (DMS)

  • Mrs. Nitaya Pirapatrungsuriya (NFI)

  • Mr. Narit Lerkoung (TISI)

ISO/IEC 17025

ISO Guide 43 Part 1 & 2

(5.9 Assuring the quality

of test and calibration

results)

WD 22117


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Participation:

4th meeting—Held on 16th of January 2007, Paris, France.

Working draft of Specific requirements for proficiency testing

by interlaboratory comparison

5th meeting—Held on 24th of April 2007, Cairo, Egypt.

Working draft of Specific requirements and guidance for

proficiency testing by interlaboratory comparison

ISO CD 22117

6th meeting—Held in February, 2008

ISO/CD 22117 of Specific requirements and guidance for

proficiency testing by interlaboratory comparison


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Objectives

  • Evaluation of performance, particularly trueness (bias) and,

  • in some cases, precision of food microbiological examinations

  • in specific laboratories.

Data from PT can be used:

  • To provide information to the organizations responsible for

  • laboratory acceptance within an official control framework and

  • to allow continuous control;

  • To aid laboratory accreditation in a general framework of

  • quality management;

  • To inform those responsible for quality in the participating

  • laboratories as part of the educative elements of external

  • quality assessment of trueness (bias).


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1. Scope

  • Food

  • Animal feeding stuffs

  • Food production environment and food handling

  • Primary production stage

  • Water

“This document is to be used in conjunction with ISO/IEC Guide 43-1 and

ISO 13528, and deals only with areas where specific or

additional details are necessary for PT schemes for food microbiology.”


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2. Normative references

ISO 13528 Statistical methods for use in proficiency testing by

interlaboratory comparisons

* ILAC Guide 13

* ISO 7218 General requirements and guidance for microbiological

examinations

3. Terms and definitions

Harmonize definitions with ISO 17043/ILAC Guide13 and WG 3

(Validation methods)

* Disassociation of statistical and microbiological terms

  • Some terms used in the text have different meanings in

  • microbiology and statistics, e.g.

    • Homogeneity

    • Heterogeneity

    • Test

    • Sample

    • Distribution (e.g. d. of micro-organisms vs. d. of test results)


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4. Scheme design and purpose

4.1 Scheme objectives

The primary objective of any PT scheme is to provide information to

enable laboratories to have confidence in the reliability of their results

The studies required to establish new PT scheme should include as a

minimum the requirements listed in section 5.

Requirements for checking individual rounds of testing, including

homogeneity and stability testing should also be established in

the scheme design and be appropriate for the scheme objectives

4.2 Laboratory requirements for schemes

Criteria for selection for microbiology schemes should include

safety advice, for example, food microbiology laboratories

with facilities for dealing with micro-organisms of Risk Categories

1, 2 and 3 as appropriate. (ISO 7218)


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4.3 Choice of test matrices

The reasons for the choice of matrix type must be stated, for example,

to provide levels of sample stability and homogeneity that are fit for

the intended purpose of the scheme. The description of the test items

must specify the sample matrix.

4.4 Information on test methods used by the PT provider

4.5 Statistical design

An outline of the statistical design for PT schemes for microbiology

should indicate that the statistical tests to be used are influenced by

the level of homogeneity of the test material.

(Low numbers, Semi-quantitative enumeration tests and

qualitative detection )


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5. Technical requirements/guidance for sample design

and content

5.1 Target organisms level

The target organisms should be provided at levels suitable to show that

examination methods are fit-for-purpose and to reflect levels likely

to be found in the sample matrices being tested.

Where pathogenic bacteria are the target, the levels should also

take account of and reflect the levels causing hazard to human health.

5.2 Organisms sources, characterization and traceability

5.3 Background/competitive flora

5.4 Matrix selection and effects


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6. Sample verification by the provider

6.1 Sample homogeneity testing – general considerations

A formal homogeneity test should be performed on each

batch of samples, based on relevant statistical principles.

(See ISO 13528, or as an alternative, annex B)

A test material which is less than sufficiently homogenous,

can still be used in a proficiency test round, by making the

target standard deviation larger than usual, in order to take

account of the greater variance between test portions

(See ISO 13528).

6.2 Homogeneity testing for quantitative/enumeration samples

6.3 Homogeneity testing for qualitative methods

6.4 Stability testing by the provider

  • Stability during storage conditions

  • Stability during transport conditions


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7. Sample handling

7.1 Instructions to participants

  • Storage conditions for samples of all types

  • Maximum temperature of the samples on receipt at the

  • participant laboratory, if appropriate

  • Instructions on how to handle the samples

  • Other supplementary instructions (e.g. the method(s) of

  • examination and How to report the results to the organizers)

8. Performance evaluations

8.1 General introduction

  • 8.2 Quantitative methods

    • Distribution of data

    • Determining the assigned value

    • Uncertainty of the assigned value

    • Uncertainty of the assigned value

    • Methods of assessing performance

    • Using z-scores

    • Other methods of performance evaluation

    • (e.g. Using the 0.5 log10 rule, percentiles, MPN)

    • Long-term performance assessment


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Annex A (informative)

Example of details to be included in a PT scheme plan

Annex B (informative)

Methods of testing for variation between portions of

Reference Materials (RM)

Annex C (informative)

A practical method to assess long-term performance of participants

in PT schemes using enumeration methods


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Resolutions from ISO/TC 34/SC 9 26th of meeting

1) SC 9 members asked the project leader (Sue Passmore) to

provide for November 2007 a draft to be submitted to CD vote by

the secretariat.

A WG 4 meeting should be scheduled one month after the closure of

the CD vote to deal with the comments and to prepare the draft for

the DIS vote.

SC 9 members asked the project leader to come with recommendations

at the next SC 9 meeting for launching the DIS.

2) In order to avoid any conflict with the revision of ISO guide 43-1

(future EN ISO 17043), SC 9 members wished to establish a formal liaison

with CASCO and asked the secretariat to write a letter to CASCO for

a formal participation in WG 4 of one member of CASCO WG on

EN ISO 17043.


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