I think a lot will depend on numbers - and luck.
We had a horrible year early on on the moorland farm, when the weather was too awful to put newborns outside, so the lambing pens were getting full and the occupants staying in them longer. We found then that rigorous hygiene between occupants (complete muck-out, sprinkle of lime, clean bedding) was essential, and we also had to muck out if anyone was in a pen for more than 3 days (a recalcitrant adoptive mother, or a first-timer struggling to get the hang of her job, or a weak lamb that wasn't yet fit to be outdoors, for instance.)
In other years, when the norm would be mothered up, suckled and outside within 24 hours, sometimes within 6 hours, we didn't have the problem and only needed the full muck-out if a pen had become very wet or soiled; a layer of fresh bedding sufficed otherwise.
The problem is that you don't necessarily realise that this year is going to be one of those years in time to have already been implementing the rigorous hygiene. So a routine squirt of Orajet to all lambs born inside (which on the moorland farm was all the mule mothers, and any Swales having triplets and any problem Swales, and here is only expected problems or anyone looking like lambing on an horrendous night) makes sure you are ahead of that game.
Most of you will know that I am the first to rant about not jumping to the antibiotics before having established that it's even a bacterial problem, but having had the experience I did when the weather gave us a really difficult lambing, I would now feel negligent if I didn't do it and lost lambs or had lambs struggle because of it.