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Friday, September 27, 2013

Porous versus Non-Porous: Who wins the trophy for most effective transmission?

The truth of the matter is any surface or fomite has the potential to transmit pathogenic bacteria, viruses or fungi.  However, the effectiveness of transmission and likelihood any surface in particular could be directly linked to transmission and ultimately lead to infection are two entirely different things.   Equate transmission to transportation.  A bicycle will get you to from point A to point B faster than walking, but the 2014 Porsche 911 Turbo which can go from 0 - 60 in 3.2 seconds is the obvious winner in terms of speed of getting you from point A to point B.

Similar to the differences in effectiveness of transportation between bicycles and sports cars, there are distinct differences in the effectiveness of transmission between hard, non-porous surfaces such as glass, laminates or smooth plastics and porous, soft surfaces such as privacy curtains, lab coats and bed linens.

There is evidence to support the fact that hard, non-porous surfaces such as tables, door handles or toilets are far more effective in transferring germs from their surfaces to the hands of healthcare workers (HCWs) than  soft, porous surfaces like fabrics.  Just using a little common sense can see how this would be true.  Fabrics, sponges and other porous, soft surfaces by their very nature have crevices, pits or divots.  What better place for germs to hide.  Have you ever used a sponge to paint or stamp?  When you apply paint to the sponge and then press it to a surface does the paint spread uniformly?  No.  There are pockets of the surface that the colour did not transfer.  The reason?  The paint was hiding in the crevices.  Similarly, these crevices decrease the effectiveness of germs transferring to hands of HCWs. 

Now picture a hard, non-porous surface such as a table or plastic touch screen.   Such surfaces do not offer the same crevices for germs to hide.  If you were to use a plastic square to stamp what would happen?  The paint would cover the surface uniformly and when you then pressed that plastic square to a surface you would get a nice, uniform square of colour.  From an infection transmission perspective a hard non-porous surface provides a far more effective transfer of germs to hands.

A 2001 study by Sattar et al. investigated how bacteria is transferred from fabrics to hands and then to other fabrics again.  I particularly like this study because the research team applied a quantitative protocol for assessing the transfer of bacteria from fabrics of 100 percent cotton and a 50-50 cotton/polyester blend to fingerpads or other pieces of fabric.  Transfer from fabric to fabric was performed by direct contact using moist and dry fabrics. Transfers from fabrics to fingerpads of adult volunteers were tested using moist, dry and re-moistened pieces of the fabrics, with or without friction during the contact. Bacterial transfer from fabrics to moistened fingerpads was also studied.  Sattar and his team concluded that bacterial transfer from moist donor fabrics using recipients with moisture was always higher than that to and from dry ones.  Further, friction increased the level of transfer from fabrics to fingerpads by as much as fivefold. Bacterial transfer from poly/cotton was consistently higher when compared with that from all-cotton material.

What does this all mean?  Well, we know that germs are able to be survive on soft surfaces such as fabrics, and certainly there is evidence that they can be transferred from fabric to hand or fabric to fabric.  But, transfer was most successful when fabric or hands were wet.  How often to HCWs touch patients with wet hands/gloves?  Are soft surfaces a true concern for infection prevention or are we simply hypothesizing that based on findings from a few studies that have show germs can live and survive on soft surfaces that such surfaces MUST then be the reservoir for all the transmission we see in hospitals?  Personally, I think not.  Hard, non-porous surfaces are still by far the most efficient in transferring and thereby transmitting disease.  I think we need to take a harder look at all of those pieces of shared patient care equipment and really investigating who is cleaning them (if in fact they are being cleaned) and how they are contributing to the spread of HAIs.

Stay tuned for next week's blog...... A New Claim on the Block!  Can you guess where I'm going with this?

Bugging Off!


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