The extent to which children should be protected from infectious illness has been much debated. In the past 30 years, there has been an epidemic of chronic inflammatory diseases (CIDs) in the industrialised world. For young children, the main concern is asthma, hay fever, food and other allergies, but the problem extends to a broad range of diseases including Type 2 diabetes, inflammatory bowel disease and autoimmune diseases such as multiple sclerosis. It may also extend to cognitive disorders such as depression and autism.
The possible link between reduced exposure to 'infection' and an increase in allergic diseases was proposed in the 1990s. The 'hygiene hypothesis' fuelled the idea that we have become too clean for our own good; and, unfortunately, this idea persists, despite substantial revision of the hypothesis to the extent that using the term 'hygiene' to describe it is a misnomer.
A more rational explanation was put forward in 2003, when Graham Rook proposed the 'Old Friends' hypothesis. He argued that the vital exposures are not colds, influenza, measles and other common childhood infections - which have evolved relatively recently over the past 10,000 years -but the microbes present more than two million years ago when our immune system was developing.
In the 1950s, our parents, armed with clean water, antibiotics, etc, were relieved to at last be free of our pathogenic enemies. What nobody realised, however, was that we had also been cutting ourselves off from our so-called Old Friends (those microbes and organisms) that occupy the same habitats. The challenge now is to reintroduce the microbes we need to our human bodies without reintroducing disease-causing organisms.
What sort of microbes do we need, when and how?
Rook says the immune system has evolved to need input from at least three sources, collectively termed the Old Friends:
- The commensal microbes transmitted by mothers and other family members.
- Organisms from the natural environment.
- 'Old' infections (including parasitic worms) that can persist in a relatively harmless 'carrier state'.
It seems probable that exposure to a diverse range of these organisms is important, particularly early in life, because they interact with the regulatory part of our immune system. Without this, the immune system can over-react, causing asthma and hay fever, or attack our own tissues, causing autoimmune diseases.
For allergic disease, it seems that the important times for exposure are during pregnancy and the first few days or months of infancy, and this exposure needs to be maintained for a significant period. This fits with evidence that Caesarean section is associated with increased tendency to develop allergies, while breastfeeding for six months or more can be protective. What we do not know is the extent to which exposure needs to be maintained during childhood and adult life, and whether CIDs could be reversed by ongoing exposure.
CRITICAL POINTS OF CONTACT
At the same time that concerns about CIDs have developed, so too have concerns about infectious disease. Gastrointestinal, respiratory, skin and other infections circulating in the community still exert a heavy toll on health and prosperity, but could be reduced by better hygiene.
These concerns are partly driven by the growing immuno-compromised population being cared for in the community. Increasingly, healthcare is delivered at home. Preventing pandemics and tackling antibiotic resistance are global priorities, and hygiene is a cornerstone of containing these threats. The need is to develop an approach to hygiene that minimises exposure to pathogens, while sustaining normal exposure to the human, animal and environmental microbes we need. Since they occupy the same habitats, this is a tall order. The approach of the International Scientific Forum on Home Hygiene (IFH) has been to develop a risk-based approach, known as 'targeted hygiene'. This can be understood by acknowledging the simple principles of how germs spread:
- Disease-causing organisms are introduced into the home mainly via people, contaminated food and domestic animals, and sometimes via water or the air.
- During daily activities, these organisms are shed on to the hands and surfaces, and into the air.
- These organisms move around the home via surfaces or the air so that, when we come into contact with enough of them, we get infected - via the mouth, respiratory tract, skin cuts and abrasions, or by rubbing the eyes and nose.
- Targeted hygiene means knowing the critical points in the chain of infection transmission, and focusing hygiene measures at these points at the right time to block the spread of pathogens.
Risk assessment shows that the critical points are the hands, together with hand and food contact surfaces, cleaning cloths and cleaning equipment. These are the superhighways for spreading pathogens around the home and nursery, either directly or via the food we eat.
Babies and children under five years of age are an important group requiring protection from infection because their immune systems are not fully developed. Children easily pick up germs in the home and nursery and pass them around the family. Handling soiled nappies can also spread infection. The main ways in which babies and infants can become infected are:
- They can get diarrhoea if harmful organisms get into their mouths either via food or drink, or they put fingers that are contaminated with germs into their mouths.
- They can develop runny noses, colds and influenza if respiratory germs (mostly viruses) are inhaled. Cold viruses can also infect by rubbing the eyes or the lining of the nose with contaminated fingers.
- Skin infections occur if germs get into cuts or abrasions on the skin.
- Babies are particularly prone to eye infections, which can be caused by rubbing the baby's eyes with contaminated hands or a dirty face cloth.
Since the hands are a major route for germs to spread, hand hygiene is probably the most important hygiene measure. Targeted hygiene, however, is good news because it is not about 'frequent handwashing', but handwashing at the right times. Risk assessment suggests that the right times are:
- after visiting the toilet
- after handling or caring for pet animals
- when returning from an outing
- after handling raw food such as meat and poultry
- before handling and preparing food for babies and children
- before caring for/handling babies and children.
In addition, you should also wash your hands:
- after changing a baby's nappy
- after handling tissues or wipes used to wipe the baby's nose, eyes, bottom, etc.
Importantly, however, there is no point in handwashing unless it is done thoroughly. Rubbing with soap and water lifts germs off the hands, but rinsing under running water is the process that actually removes germs. Where running water is not available, an alcohol-based hand sanitiser can be used. Where there is infection in the home, handwashing followed by use of an alcohol sanitiser is advisable.
It is important, though, not to be hygiene-obsessed. Babies are inevitably exposed to micro-organisms that, in addition to germs, will include some Old Friends, which need to become established as their normal gut flora, on their skin, etc. Gradual exposure to small numbers of a wide range of microbes is important for priming their immune system. Targeted hygiene is important because it focuses on protecting infants against exposure to 'infectious doses' of those harmful organisms that their immune systems are not equipped to deal with.
In the future, we will have to persuade people to view their microbial world differently. We must dislodge the ideas that children who have more infections are less likely to develop allergies, or that the problem is due to our 'Western obsession with cleanliness'. Because the terms 'hygiene' and 'cleanliness' are used interchangeably, to many people 'being too clean' implies being less particular about hygiene.
I increasingly hear mothers say 'I don't get my children to wash their hands because they are more likely to get allergies', which is a worrying trend. It's time to say otherwise.
The Healthy Schools Project
Hygiene product supplier Kimberly-Clark Professional has produced a range of education resources to help teachers educate children aged three to 11 about handwashing. For more information, go to: www.thehealthyschools project.com
- IFH offers a range of advice, training resources and fact sheets: www.ifh-homehygiene.org/factsheet/home-hygiene-taking-care-baby
- Bloomfield, SF, Stanwell-Smith, R, Rook, GA (2012) The Hygiene Hypothesis and its implications for home hygiene, lifestyle and public health: Summary, International Scientific Forum on Home Hygiene, www.ifh-homehygiene.org/best-practice-review/ hygiene-hypothesis-and-its-implications-home-hygiene-lifestyle-and- public.
Sally F Bloomfield is Honorary Professor at London School of Hygiene and Tropical Medicine, and scientific advisory board chairman for the International Scientific Forum on Home Hygiene
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