What do we mean by ‘cleaning’ and ‘disinfection’?

clean definition 2

We urgently need to decide what we mean when we use the terms “clean” and “cleaning”.

In the last few years, the accumulated microbiological and epidemiological data (and prolonged heated debate) has lead us to conclude that  environmental surfaces need to be considered alongside hands, laundry etc so on, as part of a multibarrier approach to infection prevention and control in healthcare settings, and hygiene at home. Set against this however, our current approach of “what do we do to these surfaces to break the chain of infection transmission?” is both unscientific, and also highly misleading to the people we need to communicate with.  This part of the equation is fast becoming the weak link, preventing us from maximising health benefits from infection prevention and control measures.  This really hit home on reading the different contributions to the excellent 2013 AJIC supplement by Rutala and Webber which, on one hand showed just how much our thinking about environmental surface risks  has developed, but in many papers “environmental cleaning” was used interchangeably with “environmental disinfection” which made it confusing to know what the writer really meant.

From our IFH experience of home hygiene, we know what happens when advising consumers (or equally, hospital cleaning staff) to “clean” a surface e.g. after preparing raw poultry. They will clean until the visible dirt is gone – and we know that this is not necessarily enough.  For the home, we have data showing that after cleaning kitchen surfaces with soap and water following preparation of a chicken (in the UK 60% are contaminated with Campylobacter),  surfaces may LOOK squeaky clean, but the Salmonella or Campylobacter is now spread everywhere (and in numbers up to 103 or more).   We have similar data for surfaces contaminated with norovirus-containing faecal matter from an infected person (for which the infectious dose may be very small).

As a start, we need a term to advise/communicate “this surface needs to be cleaned to a level that breaks the chain of infection” and we currently have NO way to do this.   If we accept that the term “clean” means absence of visible dirt/soil, we need a term to describe “microbiologically safe clean”, not just for consumers or hospital cleaning professionals, but also for communicating with each other as scientists.

There is also another common misconception. Some people work on the basis that “clean” means visibly clean, and “microbiologically safe clean” means a chemical or thermal disinfectant has been used.  But then how can we communicate that hand washing can make hand surfaces microbiologically safe” without need for a disinfectant.  There is a notion that “cleaning” is hygienically inferior to disinfection – but data now shows that the log reduction by handwashing with soap can be equivalent to that achieved by alcohol handrubs if done properly, and you have access to running water.  We put much effort into hand hygiene compliance, but relatively little into stressing that handwashing technique to deliver hands which are “fit for purpose” is equally important.

We need to go back to the simple principles of what we are trying to achieve – namely to break the chain of onwards transmission of pathogens by treating surfaces (hands or environmental) to reduce germs to an “acceptable level” i.e. make a surface “fit for purpose”.  This can be done in 2/3 ways – removing them, inactivation, or a combination of both. For the last 14 years, IFH has successfully used the word “hygienically clean” to mean “microbiolgically safe”, and “hygienic cleaning”  to describe the process to achieve this – which could be soap and water with rinsing – or cleaning disinfection, or a combination of both.

Guest Blogger Bio


Dr Sally Bloomfield is an Honorary Professor at the London School of Hygiene and Tropical Medicine. She is also is the Chairman and Member of the Scientific Advisory Board of the International Scientific Forum on Home Hygiene (IFH).  Through these roles Professor Bloomfield continues to develop her work in raising awareness of the importance of home hygiene in preventing the transmission of infectious disease, and developing and promoting home hygiene practice based on sound scientific principles. She is also working to develop understanding of “hygiene issues” such as the “hygiene hypothesis” and “antimicrobial resistance”.

Professor Bloomfield’s background is in healthcare and infectious disease. She has a degree in Pharmacy, and PhD in Pharmaceutical Microbiology from the University of Nottingham. Sally was previously a Senior Lecturer in Pharmaceutical Microbiology at Kings College London (1995 – 1997) and a Hygiene Liaison manager at Unilever Research Port Sunlight UK (1997 – 2001).  She has published 100 research and review papers on the subject of home hygiene and the action and mode of action role of antimicrobial agents.

The terms 'horizontal' and 'vertical' intervention leave me feeling upside down, confused

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I am no expert in HIV, but I know that ‘vertical transmission’ means something very specific:

Vertical transmission: the transmission of a disease from mother to child either during pregnancy, childbirth, or by breastfeeding.

Similarly, the definition of ‘horizontal transmission’ is well defined:

Horizontal transmission: the transfer of an infection from person to person.

So, when I read about ‘vertical’ and ‘horizontal’ interventions in a recent New England Journal of Medicine Editorial and the Controversies blog, I began to get a little confused. I have a PhD in epidemiology so don’t consider myself easy to confuse (in this particular domain), but I would have thought that a ‘horizontal intervention’ would be directed towards preventing horizontal spread of an infectious agent and a ‘vertical intervention’ would be directed towards preventing the vertical transmission of an infectious agent. But this is not how these terms are being applied. Instead, a ‘horizontal intervention’ is being used to describe an intervention applied to every patient (such as chlorhexidine bathing or hospital-wide hand hygiene interventions) whereas a ‘vertical intervention’ is being used to describe an intervention designed to reduce colonization or infection due to a specific pathogen (such as active screening and isolation to prevent the spread of MRSA). The use of the term ‘vertical intervention’ seems especially confusing, since it’s a ‘vertical intervention’ to prevent the horizontal transmission of a specific pathogen!

I fail to see how the terms ‘vertical’ or ‘horizontal’ intervention are useful when there are such well-established definitions for horizontal and vertical transmission. I think that ‘universal intervention’ (such as universal screening or decolonization) and ‘targeted intervention’ (such as active screening and isolation to prevent the spread of MRSA) make a lot more sense. These terms are already in common circulation, so I would urge those who favour the use of ‘vertical’ or ‘horizontal’ intervention to reconsider their terminology.