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Attainment of the highest level of microbiological quality for packing, transport and storage of sterile medical devices - a relevant step of the event-related program

Commercial packaging materials for terminally sterilized products such as sterilization containers, wrapped baskets, paper/film constructions and paper sheets have to meet certain requirements:

1.    Maintenance of sterility during the post-sterilization period: over a

       maximum of 5 years for commercial single-use sterilized products,

2.    sufficient permeability to remove the air inside the packaging and to

       allow gaseous sterilants such as steam or ethylene oxide to enter

       the packaging,

3.    sufficient microbial barrier efficiency to protect the medical device

       against recontamination by settled microbes, handling, and

       environmental contact,

4.    sufficient microbial barrier property against airborne microbes by means of

       filtration efficiency (ISO 11607-1).



However, it is not easy to assess a product’s sterility, that is its state of being free from all living microorganisms. A product’s sterility can not be confirmed visually or using non destructive methods – this has been an ongoing dilemma for physicians since they became aware of the need for sterility in the late 19th century.
The problems of confirming a product‘s sterile state increase if we consider the definition of sterility according to the International Standards.  According to these regulations, sterility means that the theoretical probability of a non-sterile product is equal to, or smaller than, one to one million (sterility assurance level, SAL).
Today the product’s initial sterility can be ensured by the different sterilization methods established in the past. A probability function can be derived on an experiment based inactivation curve of test organisms. The time point of achieving the SAL of 10-6 can be calculated using this probability function.


One recommendation to minimize the risk of non-sterility during a product’s shelf life consists of a careful inspection in order to identify visible failures such as cuts or breaks on gaskets, punctures, tears, wetness, water stains, loosened locks, settled dust following storage on open shelving. Release of the product should be dependent on this visual inspection (event-related shelf life). But an inherent problem is that a visual inspection alone can not assess sterility.
When using packaging with a porous component, air flow into the packaging during transport or storage challenges the gas-permeable components and requires effective filtration properties for the removal of airborne microbes. Some factors which affect this microbial challenge include:

- airborne microbial concentration in relation to particle size,

- air pressure differences between the inner of the packages and the outer

  environment caused by

  weather-influenced atmospheric pressure changes,

  transport to different heights above sea level (within buildings, by plane or

  road), and temperature variations.

The relationship between the required filtration efficiency and the microbial challenge by airborne microbes is illustrated by this figure .

The current status quo of the supply with sterilized medical products is characterized by

  +      lack of estimating the microbial challenge caused by air flow into the

          packaging during transport and storage;

  +      lack of knowing the barrier property of the porous packaging

          material against airborne microbes;

  +      lack of assessment of the continued sterility of the terminally

          sterilized medical devices throughout their shelf life.

Demonstrating the compatibility of a packaging’s filtration efficiency with the microbial challenge, i.e. the unavoidable exposure to airborne microbes during the post-sterilization period, is an important step in the quality assurance of the supply of sterilized medical devices and should be a relevant part of the event-related program. Event-related sterility means that the sterility depends on the packaging material and on factors (events) which compromise the maintenance of the sterility.
Events which can compromise sterile packaging include (see AORN journal (2007: 607–616): AORN Standards – Recommended Practices for Selection and Use of Packaging Systems for Sterilization):

* multiple handling that leads to seal breakage or loss of package integrity;
* compression during storage;
* moisture penetration;
* exposure to airborne and other environmental contaminants;
* storage conditions (e.g. type of shelving, cleanliness, temperature, humidity);
* type and configuration of packaging materials used; and
* use of sterility maintenance covers and method of sealing.

As the AORN Recommended Practices Committee states, both the exposure to airborne contaminants and the type of the wrapping material are relevant event-related factors. The loss of the compatibility of the packaging’s filtration efficiency with the airborne microbial impact during the post-sterilization period compromises the maintenance of sterility when the probability of a non-sterile item increases significantly, i.e. it exceeds 1:1,000,000. Therefore, only the selection of an appropriate packaging material with sufficient barrier efficiency and the consideration of the airborne microbial challenge can ensure the maintenance of sterility. For a data-based assessment of a product’s sterility at the point of use we need two specifics: first, data regarding the ability of the packaging material to retain airborne microbes, i.e. the filtration efficiency, and second, data of the estimated microbial challenge during the post-sterilization period.
We present the whole package microbial challenge test, which we developed for several years (Patent-Nr. US 8,053,210 B2; EP 1 485 135 B1). It was originally designed as an exposure chamber method for laboratory use. When using a mobile exposure chamber, an on-site application in hospitals can be performed.  In this way, the current airborne microbial load of the environment, for example of the Central Sterile Supply Department, is used to provide the airborne microbial challenge.
The topic is the assessment of sterility at the point of use. We are offering this program to physicians and specialised staff at hospitals and outpatient departments, the manufacturers of medical products and those responsible for health services. See references for results with the laboratory test method and the on-site application procedure.