I seem to have got away with it.

I kept the area covered with gauze for a couple of days, and there was only a single red mark left this morning when I ventured upon a much-needed bath (somewhat nervously as this was what introduced the infection last time). But it wasn't such a bad burn and hadn't blistered, and the mark appears to have shrunk in the hours since rather than getting worse :-)

It is a very odd way of getting injured, though!