I found two roaches in my house, do I have an infestation?

I saw a roach in my garage on my way to a party this past night and my Dad killed one in his office a few hours later. I don't know if it was the same one or not (tried to run over it, but I was backing out with a Sequoia, hard to be accurate with that :)), but does this mean that I could have an infestation in my house? We're a pretty clean family and the roaches were pretty big, probably adults.We leave the door open when we bring in groceries (Yes, I know they can come with fresh produce), but I guess that wouldn't make a difference if they are cockroaches with their ridiculously annoying ability to flatten themselves. I digress, anyone know?