My play group were trying to decide if outbreak effects the hero it target and each hero with in three spaces, or just any other hero with in three spaces.

The card apparently reads:
Play this card at the start of an infected hero's turn. Each hero within 3 spaces of that hero must test [might]. Each hero that fails gains 1 infection token and then suffers [damage] equal to the number of infection tokens he has in his play area.

I'd rule in favor of it including the chosen hero, as it doesn't say "each other hero."

it's this part that is open to interpretation "Each hero within 3 spaces of that hero must test [might]". I first though like you do that it would effect all of the heroes but the wording could or be read as only the other heroes test [might] as the target hero isn't a hero with in 3 spaces of it's self

No open interpretation. No "other" in the text. All heroes in range, including the first one are affected.

but the wording could be read as only the other heroes test [might] as the target hero isn't a hero with in 3 spaces of it's self

Why isn't the target hero within 3 spaces of himself? 0 is less than 3.

We've always played that the figure at the center of an effect is always within X of himself, where applicable, unless the effect specifically says "other [heroes|monsters|figures]"

The card writing is similar to the runemasters "break the rune" skill which was ruled that the runemaster is within 3 spaces of himself, hence he targets himself with his own attack (which makes the card not worth buying in my opinion).

That makes me think that this card indeed also targets the hero whos turn it is.

Yeah, I'm fairly certain FFG has clarified on multiple occasions that a hero is always within X of itself. They also have some cards which explicitly mention "each other hero" for cases where the originating hero shouldn't be included.

i had a similar issue with one of the prophets abilities, where a hero with the insight token could suffer 2 fatigue to reroll a missed attack. there too, the wording was a hero within 3 spaces of the hero with the insight token.

justin answered, that (although not written like on other cards "including yourself") ofcourse a hero is always within 3 spaces to himself

So, in roleplaying words: If a hero is infected and Outbreak card is played on him, the outbreak of his infection starts and he suffers from it more then before, infecting all other heroes near him.