According to the BBC it kills 2 to 3 people a year and infects 60 - 70, more than I expected. I've heard warnings of Weil's disease so many times without hearing anyone who suffered from it that began to take a relaxed view on it: clearly that was wrong.
One reason I probably haven't encountered it is that the bug likes stagnant water, not flowing tidal ways like the Thames. According to the Guardian he died after sculling in Boston.
Lets be careful out there.
