Is there evidence that this is 100% caused by using sweepers?
Is there anything that can be done to stop it occurring?
Not sure on evidence to be honest as not looked into it massively, but it's to do with disturbance of the ground/soil and so the bacteria Clostridium botulinum which is thought to cause it.
There is so little known about it but 'mechanical droppings removal' is given as a possible causal factor on the grass sickness charity website.
Really difficult one to prevent/plan for as so many possibilities/unknowns still unfortunately