Solving Wet Pack or Wet Load Issues


One of the most frustrating and time-consuming issues in sterilization is troubleshooting wet packs or wet loads.  A sterilized package is considered a wet pack if moisture (dampness, droplets, or puddles of water) is left in or on a package after the proper cooling period.1  Moisture on or inside a package is an issue because it can create a pathway for microorganisms to migrate from the outside to the inside of a package.2

The definition of a wet load is moisture present on or within several packages in a sterilized load after the load has dried and cooled.1   Items in a wet load should not be used and should be reprocessed.  The reason for the wet load should be investigated and resolved.

Wet packs or loads are a multifaceted concern because the cause is generally not readily apparent.  Wet packs might indicate problems with:

  • the composition of the package,
  • how the sterilizer cart was loaded,
  • the performance or operation of the sterilizer, or
  • the steam generation and distribution system.1

If the reason for a wet pack or wet load is discovered and that reason is not obvious, the organization should form a multidisciplinary team made up of members from sterile processing, OR, infection prevention and control, facilities management, and equipment repair personnel.   The multidisciplinary team should start to investigate the issues or problem(s) by asking several key questions such as:

  • Did the wet pack or wet load happen:
  • at a certain time of day?
  • at a certain time of the year?
  • only with certain trays?
  • in a specific sterilizer?
  • on a certain level or location of the sterilizer cart?
  • Is the humidity level in the wrapping and assembly area too high?
  • Was the wetness found on the outside of the pack(s) or the inside or both?1

In the fall of 2013 The Association for the Advancement of Medical Instrumentation (AAMI) released the 4th and final amendment (A4:2013) to ST79:2010, Comprehensive guide to steam sterilization and sterility assurance in health care facilities.  The amendment to ST79 includes a complete informative annex on moisture assessment (a.k.a. wet packs).

In addition to the amendment, ST79 also provides two very sensible tools relating to the investigation of wet packs.  The Moisture Assessment Check List, labeled as Table P.1 and the Moisture Assessment Flow Chart, labeled Figure P.1.  The Flow Chart gives instructions on what to do if the moisture was found at the point of use, or if the moisture was found prior to leaving the CS department etc.

The moisture assessment checklist looks at the various possible causes of wet packs or wet loads.  The checklist categorizes the issues into either processing errors or sterilizer and/or utility malfunctions.

The processing errors are categorized as:

  • practice issues,
  • load content and configuration,
  • sterilization process, or

The sterilizer or utility malfunctions causes can be from:

  • boiler system,
  • steam delivery system (piping),
  • sterilizer performance,
  • environmental issues

These two moisture assessment tools can be extremely helpful in diagnosing what could be causing the wet packs or wet loads.  Having steps to follow helps to take some of the frustration out of the investigation and perhaps eliminate some of the finger pointing that often comes with these types of issues.  All moisture incidents should be recorded and include illustrations on how the items were loaded on the sterilizer cart.  This can be helpful in the investigation as well as for any future moisture assessment incidents.


  1. ST79 – Comprehensive guide to steam sterilization and sterility assurance in health care facilities, ANSI/AAMI ST79:2010 & A1:2010 & A2:2011 & A3:2012 & A4:2013
  2. Guidelines for Sterilization. In: Guidelines for the Perioperative Practice. Denver, CO: AORN, Inc; 2017

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