So I'm looking for any kind of manga that deals with outbreaks, be they viral/animal/zombie/insect/what-have-you. Preferably completed, but not a requirement.

To give you some idea's of what I've enjoyed, take a look at:
Region
Bio-Meat: Nectar
Gyo
Cradle of Monsters

Thanks in advance!

Zennou no Noa - The World of Lostmemories although it isn't a real outbreak the people "infected" are held underground

________________
in need of romance?
uncommon, sad, sweet

not exactly outbreaks but maybe
Kiseijuu
King of thorn
La Mosca

________________

Oh, they all look interesting, I'll be sure to give them a read!

You might like Bloody monday

Dawn - Tsumetai Te, Variante (If I'm not mistaken, because it's been some time, since I flipped through it's first chapter) and maybe the storyline of Blood+ could be interesting for you. ^^

________________
"It's like love is a bonus in your life. Even without it, I'm just fine. I don't feel like pointlessly searching for it. You don't have to make yourself unhappy." (Ookami Shoujo to Kuro Ouji)

"Why does it rain?" - "To create drama." (Drops (Andou Yuki))

Some more good suggestions, but still not quite outbreak-ish. They're all on my Wish list, though, to be read.

Thanks!

Ooku
7 Seeds

________________

7 Seeds I've read and dropped - not what I'm really looking for. That other series doesn't seem to be translated :x

Ooku is licensed by Viz, which has published the first 7 volumes... Anyways, here's a few series featuring outbreaks (or the threat of one):

I Am a Hero
Manhole
Emerging (I haven't read this one, but it seems to fit)

This is more like it :3 I especially like the synopsis for Manhole. I might give it a read tonight xD Thanks!

Edit: I've got a good chunk of series to try out, thanks everyone. But if there are any more suggestions, keep 'em comming!

Maybe you would like Apocalypse no Toride

There are only two chapters translated so far, but you may consider Hakaijuu.