A lone survivor, Porter (Sean Astin), of the ferocious strain of flesh-eating bacteria is recovered by guys in hazmat suits and taken to a hidden lab in a cave on an island in the Dominican Republic. Dr. Edwards (Currie Graham) says the world is on the verge of a global pandemic an that this man is the only survivor of this disease and that his natural immunity will lead to a cure. After two months Porter begs for the experiments on him to stop and threatens to kill himself--and he ends up contaminating a lab worker on purpose, which causes a 48 hour lockdown. It also causes the waste of the lab to be flushed out into the nearby ocean, where it infects and kills the fish...
Then, we go to a group of 20-something adults who are in the area for a bachelor party. They part on a boat and end up on this island. Two of them go swimming, come across the graveyard of dead fish, and become infected. They come across the upper portion of the lab--and investigate to see if there are other people on the island. They do manage to get into the lab--and find that most of the people are infected and half-crazed from the necrotizing disease.
This is another sequel that's better than the first movie. There's some very gory scenes, such as when a guy goes to pull his girlfriend off the ground and the skin of her arms and hands comes off like gloves, and a knock-down fight between two women who are infected. Recommended.