One issue I have with many of these studies is that they are specifically looking at PTLD and not necessarily at chronic Lyme disease - and the two are not necessarily the same thing, as I tried to get to the bottom of a few months ago in my blog: https://lucibee.wordpress.com/2019/...ottom-of-the-latest-chronic-lyme-controversy/ Here's the bit where Sandra Pearson was discussing just that: Some of the epidemiological studies will follow those with diagnosed-and-treated LD forward to see if they subsequently develop late effects, and it seems that very few do. Some will try to look retrospectively, but without the ability to definitively diagnose LD without the original rash and/or serology, that's tricky too. To do both at once would be impossible. There is also the problem that although the rash is a definitive sign of LD, not everyone who is infected presents the rash. This can lead to late presentation, and if they are treated at all, late treatment is not as effective. There just seem to be multiple things that would make any epidemiological study fraught with pitfalls. If you are too strict, you will miss people, and if you are not strict enough, you will inevitably include people who have something else.