To put this into better perspective we need to look at this relative to the number of employees. From the article:
Tesco warehouse in Rugeley, near Birmingham, recorded only eight ambulance callouts in three years versus the 115 logged at a nearby Amazon site. Both warehouses employed large numbers of workers at the time – 1,300 at Tesco’s site and around 1,800 at Amazon’s.
So 6.15 calls / 1000 employees for Tesco vs 63 calls / 1000 employees for Amazon, or just over 10 times the rate.
I wonder what the differences are. Do Amazon force them to work a lot longer hours? Do they not provide air conditioning whereas Tesco do? Those two factors could make a huge difference.