Deadly allergies by population
January 21, 2015 12:11 AM   Subscribe

I'm wondering if there's any info on severe allergies and their frequency in different populations.

For example, are peanut allergies more frequent in the developed world? Also, are severe allergies showing up more in general, worldwide, than historically? Are some allergies growing by leaps and bounds that used to be more rare? Thanks for any light you can shed on this. It's just for my own curiosity, if it matters.
posted by Klaxon Aoooogah to Health & Fitness (8 answers total) 1 user marked this as a favorite
There are quite a few studies in this area. In general, like this one, and more specific. Sesame allery in Israel is one example. There's also Regional differences in EpiPen prescriptions in the United States, where the underlying factor seems to indicate that the differences found in the USA will occur on a global scale as well. (Though prescriptions of EpiPens and occurrence of allergies will not be correlated as neatly everywhere, as is commented on in this article in the NY Times.)

This query in Google Scholar could be a starting point for further research.
posted by Ms. Next at 1:32 AM on January 21, 2015 [1 favorite]

Best answer: The short answer to your question is yes.

Allergies are one of a number of clinical manifestation of atopy. The others are bronchial asthma, atopic eczema and hayfever. Although these diseases are distinct, they nevertheless have a number of commonalities at the cellular and molecular level. They are also linked epidemiologically, and people with asthma and/or food allergies almost invariably suffered eczema as a child (and a smaller but not insignificant fraction continue to suffer from eczema into adulthood). So most meta-studies generally look at these diseases together**

Broadly speaking, atopic diseases are definitely more prevalent in the western world, and they are on the rise. To go some way towards to your historical question, consider this: There is no mention of eczema, hayfever of asthma in the bible. And we're not talking about unobvious diseases here. Somebody who gets red puffy eyes in the presence of ragweed, or starts wheezing at the first sign of dust, or scratches themselves until they bleed is not something that would have gone unnoticed. These diseases simply did not exist 2000 years ago. I'm not sure when eczema started showing up, but hayfever emerged in the early 19th century and asthma emerged shortly after WWII. Nobody knows why, though there are many, many theories (as an immunologist, I have my own, but they are just as speculative).

As for severity, hospitalisations due to asthma have finally plateaued in the last 10 years after a more or less unabated rise since the 1950s. This plateau is mostly attributable to improvements in management of this disease (i.e. it's not that people aren't getting the disease anymore, they just aren't going to hospital for attacks so often). Allergies continue to grow in the western world, both in terms of the number of sufferers and the severity of reactions. It is now common practice in the western world for daycare and primary school teachers to carry EpiPens and be familiar with their use. They are practically unheard of in India.

Eczema is the hardest to get good information on. Epidemiological studies would suggest it is on the rise, but it's not the easiest disease to diagnose, and any kid with an itch nowadays has eczema. You also don't get hospitalised for eczema, which means there isn't an easy measure for severity in the population. Nevertheless, even conservative estimates put eczema at 15% in children in the industrialised world, which is monstrously high for a disease that didn't exist 200 years ago.

As you seem to be interested in severe allergic reactions, I suggest that you search for [incidence] AND [anaphylaxis] in Pubmed if you want to find the original literature on this. The continued increase in allergy is one of the great unmet challenges of western medicine. There have been literally thousands of studies into this.

**Note that you'll only ever find comparisons of rates of disease in different countries in meta-analyses. One country will report their incidence rates. Another country will report theirs. Direct comparisons in the same study are rarely conducted, which means that the meta-studies are the ones that give the picture of global trends.
posted by kisch mokusch at 3:54 AM on January 21, 2015 [11 favorites]

Note that something existing vs. being described in medical literature are not the same. There are in fact reports of deadly allergies and asthma going back thousands of years. That's a nice history of treatment, too.
posted by Andrhia at 4:13 AM on January 21, 2015 [4 favorites]

Erm, I'm a person with both asthma and food allergies who never suffered from eczema. Am I really such a unicorn? I think this is being overstated.
posted by mysterious_stranger at 8:18 PM on January 21, 2015 [1 favorite]

A child with moderate to severe atopic dermatitis has a 50% risk of developing asthma and 75% risk of developing hay fever. Likelihood of developing food allergy depends on severity of the eczema, but still in the 50-75% range.

But you are right, you can still develop these conditions independently of eczema (as you have). I don't know what the rates for that are (i.e. I'm not sure how much of a unicorn you are). Most studies focus on the atopic march, since eczema precedes the other diseases and there is mounting evidence that the eczema may actually play a causative role in asthma and allergy.
posted by kisch mokusch at 10:23 PM on January 21, 2015

You've got a pretty serious flaw in logic there. Your original assertion was that people with asthma almost always have eczema. So, if A then almost certainly B. But in your last post you've stated that a child with moderate to severe atopic dermatitis has a 50% risk of developing asthma, and a 50-75% chance of developing eczema. So, if C, then 50% chance of A and 50-75% chance of B.

Why do you think that "if A then B" can be proved by stating "if C then 50% chance of A and 50-75% chance of B"?

If 50% of snerfs are blifts, that doesn't mean that most blifts are also snerfs. It doesn't say anything at all about how many blifts are snerfs.

If I'm dead, I'm almost certainly not standing up. But it's not the case at all that if I'm not standing up I must be dead...
posted by mysterious_stranger at 11:17 PM on January 21, 2015

I'm not trying to prove anything. May statement wasn't a rebuttal of yours.
"almost invariably" is an overstatement. Back of the envelope calculations would suggest that for every 100 children in a high-prevalence country, 4 will be atopic without eczema and 24 will be atopic with eczema. That's around 80-85% (not the 95-99% that my comment implied). You're not a unicorn, but you're definitely not in the majority either.

My original comment was off the cuff. My second comment was just re-emphasising the linkage with some numbers because it is a very strong link and if the OP is going to wade through the literature it's a necessary piece of information to have in order to understand why the studies are geared the way they are. But simply, people who develop atopic diseases without eczema are hard to identify before they get develop an allergy. Kids who develop eczema are identifiable, which means they have a chance at intervention. So many of the studies that look into atopic disease and the development of asthma and food allergy are ones where they have identified and routinely followed up on at-risk patients (i.e. kids with atopic dermatitis (eczema) and/or family history of atopy).
posted by kisch mokusch at 5:49 AM on January 22, 2015

An asthmatic myself, my daughter has eczema and I understood from my reading that while asthma and eczema tend to occur within families they most likely will alternate within different generations of the same family.

Also I've known a 3 year old infant with severe eczema admitted to hospital for some days of care wrapped in steroid bandages. (I always remember the look on my friend's face when she told me her MIL didn't believe in allergies and fed the child ice cream one summer.)

Also asthma goes back in my family quite far, way further back than WW2. The immediate relative to me that had it was my uncle, born in Nigeria in about 1900 and had it all his life.

I think there may be a lack of documentation of poor people's ailments in the developing world which, coupled with comprehensive records from more affluent societies, affects the understanding of this topic.
posted by glasseyes at 8:07 AM on January 22, 2015

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