International Scientific Forum on Home Hygiene

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IFH April 2018 Newsheet


1. New review IFH – looking at media coverage of hygiene and cleanliness

2. The targeted approach to hygiene

  • Targeted hygiene by any other name

3. Transmission of infection in home and everyday life

  • Presence of human norovirus on bathroom surfaces
  • Preventing transmission of norovirus infections – impact of hygiene
  • Ugly ducklings – bacterial contamination of plastic ducks in bathwater

4.  Update on hand hygiene

  • The efficacy of ethanol against viruses in hand disinfection.
  • Hand Wiping is inferior to hand rubbing with alcohol solution

5. Microbe exposure, hygiene and immunity – beyond the hygiene hypothesis

  • Human-microbe interactions, health and disease – an overview
  • The Hygiene Hypothesis and hygiene in the age of the microbiome


1. New Review from IFH: Public perceptions of cleanliness, hygiene and hygiene issues – a survey of UK and US media coverage 1989 to 2017

IFH has recently reviewed of 54 media articles about hygiene and cleanliness, It makes interesting reading, showing the misleading reporting of this issue. Of concern is the fact that many of the inaccurate statements were purported to come from experts.

The “whopping” numbers of germs in our homes! Of 18 articles, where homes were sampled, 12 emphasized the large numbers of microbes found– ranging from 100s to 1000s to millions per sample area – but most did not say that finding large numbers is quite normal and most are not harmful to health. Microbes were mostly referred to as germs (10/18 articles) or bacteria (11/18).  More than half (10/18) used sinister terms like “disgusting, hidden, dangerous, deadly” implying that the microbes are undesirable and should be eliminated.  A few articles were explicitly scaremongering e.g: “My dishwasher is trying to kill me! ‘Deadly bacteria found”, “The kitchen sponge is 200,000 times dirtier than a toilet seat - and could lead to paralysis”.  Ten of 18 articles rated there were more bugs/germs/bacteria on the surface than on a toilet seat - figures ranged for 40x more up to 200,000x.  What’s this all about – can’t they say something more original!!
Are we too clean for our own good. Most articles (75% of 36) talked about “dirt and germs” exposure as necessary for building a “healthy” immune system.  In recent articles, urging exposure to dirt, soil or through gardening has become a recurrent theme.  Again journalists talked about ‘germs’ without saying whether this meant ‘harmful microbes’ or ‘any type of microbe”.  This is critical because it is the fundamental difference between the hygiene hypothesis which is no longer supported (that too much hygiene and cleanliness has reduced exposure to infectious microbes), and the now widely accepted Old Friends Mechanism (that lifestyle changes are to blame by  reducing exposure to the diverse mostly non harmful microbes in our animal and natural environment).  Overall, 30/36 articles (83%), even the most recent, cited home or personal cleanliness as the underlying cause of reduced exposures, despite the fact that, from about 2005 onwards, 15 (42%) of articles were quoting new data showing that lifestyle factors such as less outdoor activity/farm living, increasing C-section births, reduced breastfeeding, altered diet, overuse of antibiotics etc are the most probable causes.  Even then, 13 of these 15 articles also cited “home cleanliness or hygiene as a further example of a causative lifestyle change. Despite lack of evidence, 23/36 (64%) articles also said that overuse of antibacterials, hand santizers etc is a contributory factor, and in 14 out of 23 articles, this opinion was purported to come from an expert. 

Impact on consumer understanding The extent of the confusion in the mind of the public is illustrated by their responses to the media articles and illustrates the scepticism which the content aroused. Many expressed disbelief, otherwise “how come we are not constantly sick”. Some concluded the scaremongering is “just to make us buy antibacterial products”. 

Consumer responses to articles suggest that the public (and the journalists) still believe that the rise in allergies is “lack of exposure to Infectious germs and - since germs are largely associated with dirt, then too much household cleanliness is the cause”.  Based on public understanding of of vaccination, namely that challenge from harmful microbes/germs is needed to make the immune system strong enough to fight germs, they appear to believe the same principle applies to pollen, dust etc. When journalists asked experts what people should do to increase exposure to ‘good’ microbes, advice included more outdoor activity, getting outdoors, getting dirty, fondling pets and avoiding excessive antibiotic use.  Worryingly, it also included advice expected to increase the risk of infection – such as not washing hands!!.
Although the responses do not necessarily represent a true cross section of consumer opinion, it highlights the need to do further studies to find what consumers understand about how infections spread and the role of hygiene.  Also to find out where consumers get their knowledge, and to what extent inaccurate media reporting may be contributing to public misunderstanding and mistrust about infection risks and the importance of hygiene.

2. The targeted approach to hygiene

Targeted hygiene - by any other name

This 2017 review “Cleanliness in context: reconciling hygiene with a modern microbial perspective” essentially looks at targeted hygiene - but from a completely different viewpoint.
The review talks about how concepts of hygiene have evolved over the last few centuries, influenced by cultural norms of cleanliness, empirical data, and the germ theory of disease. Through widespread acceptance of the germ theory, the misconception that “all microbes are germs” has come to influence modern concepts of hygiene, such that it has become nearly synonymous with sterilization.

The author show how studies of skin microbiota are demonstrating that consideration of species and skin ecology is necessary to understand disease progression and devise effective treatments. Very few studies of hand hygiene examine health outcomes, such as disease transmission. Nearly all studies of hand hygiene utilize bulk reduction in bacterial load as a proxy for reduced transmission. However, due to the complex microbial ecology of  skin and the differential effects these disturbances have on different microbial species, such a proxy is likely to be inappropriate. Rather, hygienic practices should aim to reduce pathogenic microorganisms and simultaneously increase and maintain the presence of mutualistic (or at least commensal) microbes essential for host protection. It is clear that microbial colonization of the skin is not deleterious, per se. Humans are covered in an imperceptible skim of microbial life at all times, with which we interact constantly.

The authors proposes that the concept of hygiene as reduction or removal of microbial
load has outlived its usefulness, and that a definition of hygiene that uses molecular biology tools and focuses on disease reduction is needed. He proposes such a definition as “actions and practices that reduce the spread or transmission of pathogenic microorganisms, and thus reduce the incidence of pathogenic microbes, and the incidence of disease.”

They agree that it will be difficult to realize such a definition, given the inertia of current hygiene/sterilization concepts, but says “Explicit quantification of the effects of hygienic practices on health will allow us to understand the complex interplay between microbial community dynamics, hygienic practices, and health outcomes and provide data to support future recommendations for hygiene practices”. The article can be found at: Vandegrift R, Bateman AC, Siemens KN, Nguyen M, Wilson HE, Green JL, Van Den Wymelenberg KG, Hickey RJ. Cleanliness in context: reconciling hygiene with a modern microbial perspective. Microbiome. 2017 Dec;5(1):76.

3. Transmission of infection in home and everyday life

Ugly ducklings – bacterial contamination of plastic ducks in bathwater

A new study shows that rubber ducks used as bath-time toys can be a reservoir of bacteria and fungi.  The study showed that liquid released when ducks were squeezed contained potentially pathogenic bacteria in 12 out of 19 toys studied. The bacteria included Listeria spp, Legionella and Pseudomonas aeruginosa.  Fungi were identified in 11 bath toys, some of which were potentially harmful strains. One of the reasons why some microbes can actually grow and form a permanent reservoir of these bacteria and fungi in this situation is that the plastic releases carbon that can serve as a food source. Body fluids such as urine and sweat as well as contaminants and soap in bathwater add nutrients such as nitrogen and phosphorus which also help support growth.  The liquid also contained high levels of other species which are not considered harmful.

Although the potentially pathogenic species identified are normally considered only harmful to people with lower infection immunity, this includes small babies whose immune system is relatively under developed.  The study can be found at: Neu L, Bänziger C, Proctor CR, Zhang Y, Liu WT, Hammes F. Ugly ducklings—the dark side of plastic materials in contact with potable water. npj Biofilms and Microbiomes. 2018 Mar 27;4(1):7.

Preventing transmission of norovirus infections – the impact of hygiene

A 2018 study shows how microbial modelling can be used to assess the effectiveness of hand and surface hygiene in preventing transmission of norovirus infection from person to person via hands and surfaces.  In the UK up to 3 million people suffer a bout of norovirus vomiting and diarrhoea each year. In this study, researchers constructed a mathematical model, using data from a norovirus outbreak aboard a cruise ship. They estimated that wiping of surfaces with chlorine bleach could reduce the outbreak by 10% (range 3-59%)  However if 80% passengers who did not wash their hands were persuaded to change their hand hygiene habits, the outbreak would be halted. The study can be found at : Towers S, Chen J, Cruz C, Melendez J, Rodriguez J, Salinas A, Yu F, Kang Y. Quantifying the relative effects of environmental and direct transmission of norovirus. R. Soc. open sci. 2018; 5: 170602.

Presence of human noroviruses on bathroom surfaces

As many vomiting/faecal episodes occur in bathrooms, bathroom surfaces could be an important vehicle for transmitting HuNoV.  In this study, 22 reported studies of the presence of HuNoV on bathroom surfaces were reviewed. The studies involved commercial and institutional settings. Under outbreak conditions, 11 studies reported detection rates of 20–100 % on bathroom surfaces. Positive swabs came mostly from toilet seats ,but also sink faucet handles, toilet flush handles  and the bathroom door handle.  Five non-outbreak studies reported positive samples on bathroom surfaces with detection rates ranging from 2–17%. Surfaces found to be contaminated included bathroom door knobs, toilet flush handles, sink faucet handles and a bathroom light switch. Factors related to the presence of HuNoV included population density, number of employees, setting characteristics, employees’ knowledge and behaviours, and disinfection procedures.  Two studies reported that improper cleaning and disinfecting was associated with presence of HuNoV on surfaces. In a summer camp outbreak, 40% of rooms were positive for HuNoV before cleaning, 73% were positive after cleaning with soap only, but only 33% after disinfection using a 5000 ppm chlorine bleach solution. Similarly, after 2 months of norovirus illness, a hotel was closed and hard surfaces were cleaned detergent and water and carpets were shampooed and vacuumed. No disinfectant was used because of concern about fabric damage. As a result, new cases began occurring shortly after the hotel re-opened. The authors concluded that future efforts should study cleaning and disinfection interventions that reduce the presence of HuNoV on bathroom surfaces with attention given to frequency of application and training on these procedures.  The review can be found at: Leone CM, Tang C, Sharp J, Jiang X, Fraser A. Presence of human noroviruses on bathroom surfaces: a review of the literature. International journal of environmental health research. 2016 Jul 3;26(4):420-32.

4. Update on hand hygiene

The efficacy of ethanol against viruses in hand disinfection

Kampf has carried out a systematic review of the spectrum of virucidal activity of ethanol in solution or as commercially available products. Studies were selected which contained data on reduction of viral infectivity from suspension tests (49 studies) and contaminated hands (17 studies). Ethanol at 80% was highly effective against all 21 tested, enveloped viruses within 30s. Murine norovirus and adenovirus type 5 are usually inactivated by ethanol between 70% and 90% in 30 s whereas poliovirus type 1 was often found to be too resistant except for ethanol at 95%. Ethanol at 80% is unlikely to be sufficiently effective against poliovirus, calicivirus (FCV), polyomavirus, hepatitis A virus (HAV) and foot-and-mouth disease virus (FMDV). The spectrum of virucidal activity of ethanol at 95%, however, covers the majority of clinically relevant viruses. Additional acids can substantially improve the virucidal activity of ethanol at lower concentrations against, e.g. poliovirus, FCV, polyomavirus and FMDV although viruses such as HAV may still be too resistant. The review can be found at: Kampf G. Efficacy of ethanol against viruses in hand disinfection. Journal of Hospital Infection. 2018 Apr 1;98(4):331-8.

Hand Wiping is inferior to hand rubbing with alcohol solution

Ory et al. evaluated whether hand wiping is inferior to hand rubbing in reducing the
bacterial concentration on hands. In 20 healthy volunteers, hand wiping with or without an
alcohol-based solution was inferior to hand rubbing with an alcohol-based solution. The authors concluded that this finding warrants a note of caution for the application of wipes in health care. The study can be found at: Ory J, Zingg W, de Kraker ME, Soule H, Pittet D. Wiping is inferior to rubbing: a note of caution for hand hygiene with alcohol-based solutions. Infection Control & Hospital Epidemiology. 2018 Mar;39(3):332-5.

5. Microbe exposure, hygiene and immunity – beyond the hygiene hypothesis

Two new review articles by well-respected experts show how scientific thinking about how microbe:human interactions and their impact on our health has now gone way, way beyond the so-called hygiene hypothesis:

Human-microbe interactions, health and disease – an overview

In a lancet article, Rook et al review our place within the microbial world – rather than their place in ours, Their viewpoint is that human metabolism is a tug-of-war between managing beneficial microbes, excluding detrimental ones, and channelling as much energy as available into other essential functions. They discuss how this tug-of-war shapes the passage of each individual through life (eg, how fast to grow, when to mature, and how long to live). Since the evolution of cellular life, the biosphere has been dominated by the Bacteria and much of the human genome originated in microorganisms, all vertebrates harbour large communities of microorganisms, and at least 20% of the small molecules in human blood are products of this microbiota. Changing human lifestyles and medical practices are disturbing the content and diversity of the microbiota, while simultaneously reducing our exposures to organisms from the natural environment with which human beings coevolved. At the same time, however, population growth and crowding is increasing our exposure to novel pathogens, particularly the “crowd infections” that were not part of our evolutionary history. Thus some microbes have co-evolved with human beings and play crucial roles in our physiology and metabolism, whereas others are entirely intrusive. This review can be found at: Rook G, Bäckhed F, Levin BR, McFall-Ngai MJ, McLean AR. Evolution, human-microbe interactions, and life history plasticity. The Lancet. 2017 Jul 29;390(10093):521-30.

The Hygiene Hypothesis and hygiene in the age of the microbiome

Markus J. Ege has written an article which, like the Lancet review discusses how the age of the microbiome has promoted evolutionary thinking, but also how this thinking offers a key to understanding the rise in inflammatory diseases. He also talks about how the idea of co-evolution of man and microbiome has finally replaced the concept of struggle between pathogen and host - ultimately, microorganisms are neither friends nor foe, nor are they missing.  He clearly emphasises “we do not live in a sterile world with too much hygiene - we are just in an era of rapid changes, which will trigger evolutionary adaptation to an altered balance between man and microbiome”. His overall conclusion is “The increase in noncommunicable diseases merely reflects an adaptation that lags behind in a world of fast and profound environmental changes. With growing insight into the interplay between man and microbiome, we might take over a more active role and enhance adaptation through an adequate choice of microbial exposure. Although complete restoration of a pre-industrialized microbiome is an illusion, comparison of populations with diverse microbial environments may offer some guidance”.  The paper can be found at: Ege MJ. the Hygiene Hypothesis in the Age of the Microbiome. Annals of the American Thoracic Society. 2017 Nov;14(Supplement 5):S348-53.

Published: 12/04/2018

Publication Type: Newsletter