ERP Micro December 2019

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demonstrating no statistical difference in detection between lots and no significant time slope is

required. This study is carried out with pure culture.

3.4.1 Culture E . coli O157:H7 in mEHEC media, 10–18 h at 41–43°C. Dilute with sterile mEHEC media (if necessary) to a level that yields fractional recovery by the EHEC

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ID method.

3.4.2 Culture C. freundii in BHI at 37°C for 20–24 h. Use without dilution. 3.4.3 Test each lot of test kits with 10 replicates of diluted E . coli O157:H7 and 10

replicates of undiluted Citrobacter in a randomized blind coded fashion.

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3.4.4 Decode, calculate POD values and confidence intervals and analyze data for

variable detection between lots/time points.

3.5 Matrix Study: Data Analysis

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3.5.1 For each test organism, each level of each matrix must be analyzed separately. 3.5.2 Calculate the probability of detection (POD) as the number of positive outcomes divided by the total number of trials. Estimate the POD with a 95% confidence interval using the LCF AOAC Binary Data Interlaboratory Workbook ( 456 ) for:

3.5.2.1 the candidate presumptive results (POD CP ), 3.5.2.2 the candidate confirmatory results (POD CC ),

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3.5.2.3 the candidate method results taking presumptive and confirmatory

results into account(POD C

), and

3.5.2.4 the reference method (POD R ).

3.5.3 Compare the presumptive and confirmatory results of the candidate method by

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determining the difference between the POD values (dPOD CP

) for each matrix and

concentration:

dPOD CP

= POD CP

- POD CC

where dPOD CP

is the difference in POD values between the presumptive and

confirmed results at a given concentration. If the confidence interval of a dPOD does not contain zero, then the difference is statistically significant at the 5%

level.

3.5.4 Compare the candidate and reference methods by determining the dPOD C for

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each matrix and concentration:

dPOD C

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= POD C

- POD R

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where dPOD C

is the difference in POD values between the candidate and

reference methods. If the confidence interval of a dPOD does not contain zero,

then the difference is statistically significant at the 5% level.

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