We were running through a town and as we expected we aggroed about 5-6 zombies. When we got out of the town and nearly reached the next one(about 100-200 meters) we started killing them because even though we were sprinting they caught up and started hitting us causing bleeding. As we killed them they respawned 5 meters away from as and aggroed again immediately. And this went on for 10 minutes when finally none of them respawned next to us.