They did a blood test survey at a BCRA conference many years ago and most of the samples showed the 'usual' UK varieties of Leptospirosis. The people that knew they had been infected had the nasty foreign types. OK, it's not very good to extract statistics from this as the conference is, by nature, full of the 'hard-core' types who are most likely to expose themselves the most to the chance of infection.
Most of us would put our first dose down to the flu, or really dodgy beer! I assume that we are topped up on a regular basis.
Places like Stoke Lane Slocker and anywhere else rat urine (& farm waste) enter a system is a potential hazzard. You can contract it through all the usual methods including the eyes.
Leptospirosis was so prevalent at one point that the British Canoe Union set up some kind of special, fast access diagnosis system.
Of course you have all told your doctors that you are cavers and that this is a potential hazzard?
I've not looked into the problem in years, so I'll not give too much detail, in case I mis-remember something.