Hi encleadus,
Great job on organising - that's a passion of mine... I should have been a librarian or something!
I've given a lot of thought to how to structure the data and, as was said on here, I think the most important aspect is the date order of occurences. As much as I love the year/country order that you put together, it doesn't make it easy to see the most recent infection and maintenance would be a little more tricky.
When I have some time (in between battling the spyware and everything else

) I will look at it again and see what I can glean from your structure.
Thanks again!!
Lynda