News & Articles

Are Rigid Containers as bullet proof as they are perceived to be?

At the WFHSS Congress in Brisbane, Harry Shaffer from Colorado presented the results of independent research he carried out to compare the effectiveness of rigid containers versus wraps in protecting against the ingress of bacteria through the Sterile Barrier System (SBS), and came out with some alarming results.

Much of the study has been published in an article entitled ‘Sterility Maintenance Study: Dynamic Evaluation of Sterilized Rigid Containers and Wrapped Instrument Trays to Prevent Bacterial Ingress’ (Shaffer, HL, et al (2015) AJIC 43, 1336-41).

In the USA, there are reported to be 300,000 surgical site infections (SSI) a year and, from these, 9000 lead to deaths.  The average cost of each SSI for an institution is $27000, and thus the cost to US healthcare is $112 billion pa.  Is some of the source of these SSIs potentially from contaminated instruments – are the SBSs around instrument sets doing their job?

Standard industry testing of containers is covered by ISO 11607, ANSI/AAMI ST77:2013 and AS 4187:2014, but the standard tests are in a static pressure-controlled environment. However, one of these standards does also recommend (5.9.1.1) that ‘expected stresses’ in day to day usage should also be tested for.  In real life, premature extraction from a sterilizer, storage, and transport conditions involve temperature fluctuations and air movements that can lead to up to 2 PSI pressure differences, and therefore have potential to affect the SBS. 

Bearing this in mind, Shaffer designed a chamber that could hold eight packs, whether rigid containers or wrapped trays, and exposed them to an atmosphere containing 225 cfu/litre of bacteria (a level that might be found in normal air).  The chamber then underwent 2 pulses of 1 PSI pressure change then 3 each of 0.7 and 0.4 PSI.  Agar dishes inside the SBS were used to measure for any ingress of bacteria under these simulated usage cycles.

Shaffer tested used rigid containers from 14 different hospitals, and 4 different designs of new rigid containers.  He also tested 3 grades of sterile barrier wrap packaging systems.  The results from his studies showed that 87% of the rigid containers showed an ingress of bacteria, and in fact 72% of the brand new containers showed an ingress!  In contrast, not one of the wrapped packs had shown any ingress.

When one looks at the rigid containers, it is clear that they all have potential ‘weak’ points, and the more sophisticated they are, the more weak spots they may have, whether it be the lids, the gaskets, the filters and their housings, valves, etc.

This presentation at the 2016 WFHSS congress follows last year’s presentation at the WFHSS congress in Lille where a paper warned of the too-high percentage of containers that still had water condensed inside them after the completion of the sterilization cycle.

The article in the AJIC mentioned above has stimulated a high degree of international interest. In Germany a meeting was convened in Berlin earlier this year to discuss the content and implications of the US study.  The outcome of the meeting is summarised in Zentralsterilisation/Clinical Service (Issue 4 of 2016, p257 (German) and 259 (English).  This article refers to a follow up study where the bacterial load was reduced to 2 cfu/litre of Micrococcus luteus, and still 60% of the containers had ingress of bacteria. The principal conclusion the group came to was that if containers are being used, the inner load should be enclosed in a flexible wrap to ensure the instruments remain sterile.