The best we're going to do is a careful case control study (and research in animal models). And the evidence is enough to imply strongly that we should expend a little more effort to avoid removing the thymus.
But that's exactly what we did with the appendix, multiple times [1, 2].
If the standard of care is removing the appendix, and you have a strong reason to believe that something less may be superior, you may be able to conduct a randomized trial.
But any other combination of facts is going to be hard for an IRB to swallow.
Do you have any citations for that? Perhaps it differs by city and region, but many modern cities with good sanitation systems are exceptionally clean - you're not getting frequently reinfected by others' gut flora unless there is a catastrophic problem with the sewer system. People with things like C. difficile infection can have chronic disease for years, and fecal transplants have only recently been recognized as a good treatment in those cases - point being you have to have an actual fecal transplant, you're not just going to "get reinfected with healthy microbiome from sharing germs with all the other humans".
It would be interest to see how historically contact with X other people has changed over time. I don’t think you need a big city to mix with a lot of people. I imagine in older times there are fewer people but likely to be closer to each other - people sharing beds (not stupidly associating bed with sex) and tribes of families mingling close lower instead of nuclear family. By contrast the city apartment is the hermetic seal around a small number of people choosing to live together. But a modern concept: corporations, jobs and careers ensure people keep mixing up with people outside.
[0]: https://en.wikipedia.org/wiki/Appendix_(anatomy)#/media/File...
#/media/File:Appendix_function_diagram.svg){kind=link}
We both have our appendix.
Though to your point, whether you can develop a milk allergy later in life I am not sure.
If so a confidence interval of 1.02 to 2.2 after arbitrarily excluding some data is not exactly ground breaking.
Not vestigial evolutionary speaking, but doesn't it get less and less functional over a person's lifespan and gets replaced with fat tissue?
From Wikipedia[1], “The appendix was once considered a vestigial organ, but this view has changed since the early 2000s. Research suggests that the appendix may serve an important purpose as a reservoir for beneficial gut bacteria.”
> For the study, Kooshesh mined data from 1,146 adult patients who had undergone thymus removal, alongside demographically matched control patients who had undergone similar surgeries but kept their thymus
Sure, you can demographically match all you want, but I don't think this is a research question that can be answered with a retrospective analysis. The problem is that you haven't controlled for why surgeons decided to remove the thymus in some cases and not in others. Was the disease more severe in patients who got thymectomies? Was it differences in training between the surgeons? Was it just an arbitrary decision on the part of the surgeons? This is a critical confounder regardless of whether you've matched the demographics. You really need a randomized control study to answer this sort of question.
> Although the risk of autoimmune disease did not differ substantially between the groups in the overall primary cohort (relative risk, 1.1; 95% CI, 0.8 to 1.4), a difference was found when patients with preoperative infection, cancer, or autoimmune disease were excluded from the analysis (12.3% vs. 7.9%; relative risk, 1.5; 95% CI, 1.02 to 2.2)
What? What is this? Was this subgroup a preregistered, or did they just go fishing when their primary hypothesis didn't pan out?
I'd categorize this study as noteworthy, but not groundbreaking the way the press statement is selling it.