Forget the hygiene hypothesis until there is a good study

A new paper in PLoS Negl Trop Dis this week reports

The hygiene hypothesis is accepted by many in the global scientific community […] However, aspects of this hypothesis are based on assumptions that may not fully account for realities about human helminth infections. Such realities include evidence of causal associations between helminth infections and asthma or inflammatory bowel disease

Talking about realities may help proponents of the hygiene hypothesis who are stuck in a never ending loop publishing  observational studies.

Even the NEJM contributes to the hygiene hysteria hype this week. Although the allergic rhinitis prevalence isn’t so much lower in old order Amish (who are even a heterogenous group), the difference to Hutterite is being highlighted. I do not even understand the study design here as it is neither cross-sectional, nor case-control nor cohort study. Is it just an exposure description in two different groups?  Conclusions like

sustained microbial exposure was also reflected in the phenotypes of peripheral innate immune cells in the Amish.

are strange if we believe that we humans carry more bacterial than human cells. And every smoker encounters a 120fold endotoxin concentration compared to ambient air – without getting rid of asthma or allergy.

The results of our studies in humans and mice indicate that the Amish environment provides protection against asthma

is certainly wrong – nobody knows if this is an environmental or genetic or iatrogenic factor. The key finding is IRF7 expression but unfortunately IRF7 plays a critical role in the innate immune response against viruses – and not bacteria/endotoxin…