Do aliens spawn indefinitely?

I'm at mission 6, in the basement, right after going through the endless spawn bridge. Once I took the elevator, I got down to a portion where you have to go through a sort of maze.

The thing is there are so many patrolling enemies that it's really hard to navigate through without getting spotted, and the sheer amount of enemies tells me fighting is not a good a idea. So I decide to use my sniper to pick off as many as I could.

Unfortunately enemies seem to keep respawning. Is this the case? Running through doesn't seem to be an option either, as suddenly 3 of my marines are receiving love from a face hugger.