Poor Science Writing and the Hygiene Hypothesis

There is an op-ed article in todays NYT by Jessica Snyder Sachs called "Nice Shots". It concerns one of my favorite topics...the hygiene hypothesis (and here and here). The hypothesis, formed by D. P. Strachen in 1989, is that children that are raised in modern "clean" environments develop more allergies in later life than children raised in less clean environments. This makes sense because our immune system evolved under conditions where we were under constant attack from pathogens.

Unfortunately, Ms. Snyder Sachs starts with the premise that children are not being vaccinated because parents are aware of the hygiene hypothesis and thus think that illness is "good" for children.

More parents than ever before — nearly 65 percent — intend to vaccinate their young children this year, according to a poll by the University of Michigan. But that leaves more than a third unenthusiastic about doing so. Their reluctance may reflect not only weariness with the increasing number of childhood immunizations but also the widespread sentiment that colds and flus are a “natural” part of childhood, even vital for toughening up a developing immune system.

I doubt that is the reason. More likely parents have bought into the idea that childhood vaccinations cause autism. Ms. Snyder Sachs goes on:

Dr. Strachan’s original hygiene hypothesis got a lot of press, not only in the news media but in serious medical journals. Less publicized was the decade-long string of follow-up studies that disproved a link between illnesses and protection from inflammatory disorders like allergies and asthma. If anything, studies showed, early illness made matters worse.

For some reason Ms. Snyder Sachs assumes that the hygiene hypothesis states that you must be exposed to disease causing germs to result in later protection from allergy. She also assumes that the hypothesis means that exposure in early life to a "dirty" environment will protect you from other diseases in later life. The hypotheis does not say that.

I don't know how much press Dr. Strachan received concerning his hypothesis but I do know that the average immunologist is only vaguely familiar with the hypothesis. As for recent results disproving the hypothesis, that is a load of bunk. The hypothesis is as valid as ever, although the originally proposed mechanism of action is probably wrong. There are more up to date immune mechanisms that explain the hygiene hypothesis.

Ms. Snyder Sachs somehow has jumped to the conclusion that early exposure to respiratory disease-causing bacteria and viruses are the basis of the hygiene hypothesis.

A second misconception common among vaccine-shunning parents is that there’s something “natural” about the 6 to 10 respiratory infections the typical American child gets every year (or even the two to four we adults experience). Common, yes; natural no, not if “natural” represents the forces that shaped the human immune system during all but the last sliver of our 250,000 years as Homo sapiens. Colds, flus and most other contagious diseases found a central place in our lives only after we and our domestic animals began crowding together in large settlements some 5,000 years ago.

In reality the culprit is more likely intestinal worm infections. Prior to the 1950's a large proportion of individuals, especially children, harbored intestinal worm infections. The most common worm infections, pinworm and whipworm, do not cause serious disease in most individuals. These worms are also easily spread to others by contamination.

Ms. Snyder Sachs writes of the "calming" effect on the immune system caused by infection with organisms that do not result in disease. One of the problems with science writing, especially in op-eds, is that you tend to make overly simplistic statements due space constraints. Most bacteria, "good" or "bad", can induce physiologic changes in the body. The point here is how one defines "disease". As for the "calming" effect on the immune system....that statement is just embarrassing coming from a science writer.