A new approach to researching the hygiene hypothesis

Worried about your kids’ health? Hoping to improve it by letting them eat dirt, lick the cat, sneak a sniff from a smokestack, ask their friends to cough in their face and never ever wash their hands?

This would seem to be the message of the subversive view of modern life that goes by name of the hygiene hypothesis.

The hypothesis argues: The reason why there is so much asthma, eczema, allergies and maybe even childhood diabetes in the modern world is because we — well infants really — live in too clean a universe. What our baby immune systems need is a kickstart by exposure to viruses, bacteria, worms, pollutants and so on. If you don’t get an infant hit from these icons of uncleanliness, the immune system goes haywire and your body over-reacts to all sorts of invasive things that normally could be ignored.

The hygiene hypothesis itself is a theory with Canadian roots, as some have traced it back to a study done in Saskatchewan in the 1970s, which found higher rates of allergies among white southerners than among Métis northerners. The researchers postulated that allergies were "the price paid by some members of the white community …for their relative freedom from diseases due to viruses, bacteria and helminthes [worms]."

But the hygiene hypothesis' entry into the popular consciousness was a paper by British doctor David Strachan in 1989, which noted that hay fever and eczema were higher in families with fewer children, perhaps because brothers and sisters primed immune systems by infecting their siblings.

What followed was a deluge of studies relating protection from asthma/allergies to — among other things — having pets, living on a farm, being born at home, and living in heavily polluted areas. One extreme example of the latter was that children in generally clean West Germany were twice as likely to have allergies as children in extremely polluted East Germany. And when their air was cleaned up, the East German numbers started going up.

Conflicting research

A data-simple person might start to think that with all this evidence piling up that at some point the hygiene hypothesis might turn into a "dirty is better" verity. That school health classes might be on the verge of teaching children how to get filthy, and advertisements telling you "don’t wash your infants’ hands" might start appearing on TV.

Well … no. The truth is that almost every week there is a hygiene hypothesis study that contradicts the previous one.

Last month, for example, a Finnish analysis of daycares found no elevation in the asthma/allergy/dermatitis rates of children who had been in daycares where a program of rigorous alcohol-based hand washing had been used. This was the case even though the clean-handed kids reported significantly lower levels of coughs and sore throats and diarrhea and antibiotic use than a control group of dirty-handed kids.

This was countered by a study in April by a group of Canadian researchers. It concluded that, "antibiotic use in early life was associated with the development of childhood asthma."

That result seemed to follow a study by British Columbia researchers last year, which found that "exposure to at least one course of antibiotics in the first year of life appears to be a risk factor for the development of childhood asthma."

Oops, wait a minute; their paper resulted in a stern rebuke by Juan Celedon of the Harvard Medical School. He pointed out that his own and another meta-analysis — a study of studies — had found that antibiotic use "is a very unlikely explanation for the increased prevalence of asthma in industrialized countries."

The B.C. researchers responded a bit apologetically: "While we do agree that it is unlikely that postnatal antibiotic use is the sole reason for the increased prevalence of asthma in industrialized countries, there remains potential that it is a contributing factor."

Drawing conclusions

So what’s a parent to do if they're worried about the future health of their kid living in a one-child, petless, urban, cleaning-woman-twice-a-week, antibiotic friendly household?

The problem, as all the researchers agree, is that none of the studies truly control for everything you want to control for.

What we haven’t had are baby human lab rats in a rigorous hygiene hypothesis experiment. Imagine one set of children leading their early lives in a quasi-sterile environment while another group roams through dung hills, breathes polluted air, and dines on half-rotted foodstuffs.

Failing this singularly grand experiment, all we have is confusion because all we measure is portions of a whole. If pets make a difference, does it matter what kind of pet? Do dogs that shed confer more benefit than ones that don’t? If family size makes a difference, is there an optimal healthy family grouping? The Finnish daycare only measured kids of about a year old — does age make a big difference? Does the type of antibiotic a child might take matter, or the age it was given, and so on, and so on.

Even to an amateur, the possible confounding factors seem endless. Living dirty is not, it turns out, a single thing. Rather, it's a phalanx of behaviors and circumstances. Simply seeing what effect antibiotics might have on the latter development of asthma "will likely not be achievable with a prospective [that is specifically designed] clinical study," pessimistically wrote the B.C. group.

But it seems to me that this doesn’t mean a resolution to the question of whether dirtiness is next to healthiness is impossible. What we need to do is set up a virtual experiment that presumes that the world’s parents have turned into child-behaviour-recording Blackberry/cellphone/computer junkies. That is, presume what we already believe to be the case.

In this experiment we — government, hospitals, philanthropists — pay parents to track their kids’ behaviour and circumstances for a year or two. Their fees are a function of how well they monitor. But — and this is a very important but — they report their findings as a blog. We make recounting their kids’ daily doings something they can ship off to friends and relations. We make collecting vast amounts of family information — and this is a word you will almost never hear in clinical studies — fun.

I repeat, you don’t force parents to change their naturally dirty or clean behaviours or circumstances; you induce them to remember it. There would be some guidelines as to what has to be reported — say when your kid took an antibiotic and how much — but all within the context of a blog.

I suggest this radical reformation of a clinical trial, because sometimes scientific thesis are very difficult to test for, but still may be vital to human health. That could be the hygiene hypothesis — if we don’t find proving or disproving it so frustrating that we end up washing our hands of the entire concept.