I've noticed the same break out in the past couple of weeks. I think the sweat etc is definitely the culprit. It's hard for me to wash my face or shower because I work out before coming into work.
What I've started doing, though, is putting a few cotton balls in a ziploc bag with a bit of astringent poured in with it. Then, after I work out, I just wipe my face down with the astringent - and that seems to have worked out well.
Just a matter of getting all that gunk off