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Hidden Microbes: Are carpets full of bacteria?

Feb 3, 2021

Part of our hidden microbes in the home series:

Carpets

Do you hoover your carpet a couple of times a week and maybe clean it every so often? This is what most of us do. However, depending on if you're a 'shoes on' household and / or have pets, you may want to consider an extra carpet clean now and again.

Due to the fabric structure of carpet, dirt can get trapped easily. You may not consider carpet cleaning high on your list of priorities, but it is likely you wash other household textiles more regularly. Carpets seem to have become the more neglected of our home furnishings, yet they are one of the most likely to contain multitudes of micro-organisms.

A quick google will reveal headlines and articles screaming that 'carpets are 4,000 times more dirty than a toilet seat!'. Dramatic news articles aside, the consequence of having a soft furnishing in your home that is used daily and not regularly thoroughly cleaned, does mean that whether it looks like it or not, it will be harboring a variety of micro-organisms.

Debris that can become trapped in carpet fibres:

  • Mud
  • Dust
  • Food particles
  • Pet hair
  • Pollen
  • Human skin / hair
  • Ash / soot from an open fire
  • Pet 'accidents' (the less we say about this the better!)

The worst offenders are probably you or your pets bringing in coliforms and other bacteria on your shoes or their feet.

On the surface, this may not seem much of a problem as generally people don't eat off of a carpet! However, some people do like to follow the 5 second rule when it comes to dropped food and crawling infants and their toys will come into contact with carpeted areas regularly.

Of course, dust mites and allergens can also be a big problem especially for those that are sensitive to them.

When moving into a new house, it is advisable to clean the carpets as you don't know the last time that they were cleaned.

When cleaning carpets, make sure that the area is fully ventilated with good airflow and that the carpet will be able to dry quickly. Excessive moisture will just add to your micro-organism woes as carpet can become a perfect home to mould (this is also why carpet in a bathroom is a no no).

Steam cleaning and professional cleaning is often recommended.

Spilled liquids should really be dealt with straightaway (no matter how tempting it might be to leave it for later or cover it up with a foot stool or similar!).

If we look at one aspect of how carpets become contaminated (wearing shoes in the house), we can see how much bacteria can be potentially transferred to the carpet. Dr Charles Gerba a professor and microbiologist at the University of Arizona conducted some research on this. His findings were that:

‘Coliforms* were detected outside of the shoes on 96% of the shoes. E. coli was detected on 7 of the shoe bottoms (27%). No coliforms were detected on the inside of the shoe.
Transfer of bacteria from the shoes to uncontaminated tiles ranged from 90% to 99%.’

*fecal bacteria

Bacteria on shoes

These findings alone give an idea of the potential sum of microbes lurking in carpets including pathogenic bacteria. Not forgetting that shoes can also pick up allergens from outside such as pollen.

In an experiment to give an idea of what a normal, heavily used carpeted area in a household might reveal on a dipslide, we took samples from one of our team's home office carpet. Shoes are not worn in this house but there are two indoor cats in the household. The carpet is hoovered regularly and has been cleaned using a carpet cleaner multiple times in the four years that our colleague has lived there. A random patch of carpet was tested.

The results

Total bacteria count: 
When calculated as colony forming units per cm, the result was ≈40CFU/cm2 (248 Red Spots)

Yeasts and moulds count:
No mould grew on the slide, only yeast. When calculated as colony forming units per cm, the result was 12cfu/cm2.

You can see the image of our carpet dipslide test below along with others we have conducted in the past for comparison.

Carpet Bacteria

It should be noted here that only the top layer of the carpet was tested and the deeper pile underneath will not have been reached by the dipslide.

Our little random experiment shows that even a household where shoes are not worn has carpets that will require regular cleaning to keep bacteria levels down. However, it was not absolutely teeming with contamination. We didn't use our selective dipslides for this experiment, so we only know the total aerobic bacteria count rather than what specific micro-organisms are present.

In conclusion, most of us have carpets and have never really worried about what bacteria lurks in them before. This being said, there's no need to over worry about this. Regular vacuuming, carpet cleaning and maybe leaving your shoes at the door should mitigate any possible dangers. You probably should retire the 5 second food rule though! Oh and you may want to give your doormat a clean now and again.

References

1. https://www.ciriscience.org/a_96-Study-Reveals-High-Bacteria-Levels-on-Footwear

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