I realize this is a fairly new game, but a handful of friends and I were playing last night and got to the first level where you can get "infested" by the parasite head-crab aliens.
The game prompts you to heal to counter it, and even on normal difficulty our Medic was going through 2 group heal beacons each time just to prevent death. I feel like either we're missing something or this is just a rather annoying game mechanic that feels a tad overtuned at the moment.
Note that our medic did not have the medic gun, as we weren't high enough level to unlock it yet.
Best Answer
Healing seems to be the only way, but there are some methods that can help avoid infestation or - if you got infested after all - get enough healing in time: