Ugh! What’s Causing these Wet Packs?

Wet pack 2

Wet pack 3

Wet packs are a concern because the moisture on or within a package can create a pathway for microorganisms to migrate from the outside to the inside of a package.1  A package is considered a wet pack if moisture in the form of dampness, droplets, or puddles of water are left in or on a package after sterilization and the proper cooling period.  Moisture present on or in several packages of a sterilized load is considered a wet load.2

In my experience, one of the most time-consuming and frustrating sterilization issues is troubleshooting wet packs/loads.  Wet packs/loads are a complex issue because the cause is frequently not obvious.  Wet packs might indicate problems with:

  • Package composition,
  • Loading procedures,
  • Sterilizer performance or operation, or
  • The steam generation and distribution system.2

When investigating a wet pack or wet load issue, healthcare facilities should form a team to include members from sterile processing, OR, infection prevention and control, facilities management, and equipment repair personnel.  Moisture incidents should be recorded and include illustrations on how the items were loaded.  This can be helpful in the investigation as well as for any future moisture assessment incidents.

The team should begin by asking investigative questions such as:

  • Did the wet packs 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?
  • What is the humidity level in the wrapping and assembly area?
  • Is the wetness on the outside or inside or both?2

In November of 2013, the Association for the Advancement of Medical Instrumentation (AAMI) released the 4th amendment (A4:2013) to ST79:2010Comprehensive guide to steam sterilization and sterility assurance in health care facilities.  This latest amendment to ST79 includes an entire annex on moisture assessment (wet packs).  In addition, ST79 now includes two very useful tools relating to moisture assessment:

  • Moisture Assessment Flow Chart (Figure P.1 below), and
  • Moisture Assessment Check List (Table P.1)

The moisture assessment checklist looks at the various causes of wet packs/loads.  The checklist categorizes the issues into either:

  • Processing Errors
    • Practice Issues,
    • Load Content and Configuration,
    • Sterilization Process, or
  • Sterilizer or Utility Malfunctions
    • Boiler System,
    • Steam Delivery System (piping),
    • Sterilizer Performance,
    • Environmental Issues

These two moisture assessment tools can help take some of the frustration out of investigating the cause of wet packs or wet loads.

 Wet Packs


  1. Recommended Practices for Sterilization. In: Perioperative Standards and Recommended Practices. Denver, CO: AORN, Inc; 2014
  2. 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