Table of Contents

FDA MANUAL OF INTERPRETATIONS

Interpretation Number: 03-VIII-.03-100

Model Ordinance Chapter VIII.03
Reference:

Key Words: Vibrio vulnificus, matrix, AMMWT

Question:

What is the procedure for calculating the average monthly maximum water temperature (AMMWT) used in applying the Vibrio vulnificus control matrix?

Interpretation:

The state shellfish control authority shall determine, for each shellfish growing area, the AMMWT for each month using historical water temperature data for each of the previous five (5) years.

The procedure for calculating the AMMWT for each shellfish growing area is as follows:

1. List the maximum water temperature recorded for each day of the month.
2. Calculate the average maximum water temperature for the month using the daily water temperatures listed in step 1. NOTE: If water temperature data are not available for each day of the month, then use temperature data for those days it is available. These data shall be representative of water temperatures observed throughout the month.
3. Perform steps 1 and 2 for each month for each of the previous five years.
4. Determine the AMMWT by calculating the mean of the five (5) average maximum water temperatures from step 3 for each month.

Rationale:

The procedure outlined above is consistent with the intent of the 1995 ISSC to calculate the AMMWT using maximum daily water temperatures, not the single warmest water temperature recorded during the month. This procedure is identical to that used to calculate average maximum monthly air temperatures (AMMAT) required under Chapter VIII.03.

Contact:

U.S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
5100 Paint Branch Parkway (HFS-628)
College Park, MD 20740

Distribution:

Shellfish Specialists
Regional Federal State Program Managers
Division of Federal State Relations
Division of Cooperative Programs
Interstate Shellfish Sanitation Conference