Normal tongue-eating lice are confined to watery environments, but the mutant isopods in the film can survive on land as long as they have hosts. Who is to say that the isopod infestation hasn't spread to other areas via infected birds, land animals, or humans? To boot, since the govenment covered up the Claridge catastrophe, the public would have no way of knowing if similar isopod outbreaks are taking place.
Some of the filtered water from the desalination plant goes to the chicken farms. The number of chickens in those kinds of places ranges in the thousands. While we never hear anything about it in the film, the chickens being infected with isopod larvae is not outside the realm of possibility. While it's unlikely that any of the infected chickens would be butchered and sold due to the speed at which the isopods mature, there is still the possibility of the farms being overrun with numerous isopods coming out of the chickens...
At the end of the film, viewers learn that the government sterilized the Chesapeake Bay with chlorine to wipe out the mutant isopods. Since the isopods had moved on land and infested Claridge, the government would have likely resorted to a scorched earth policy to kill mutant isopods in the town. In other words, Claridge was likely burned or bombed once emergency responders rescued survivors and gathered information on what happened.
Jennifer's situation is pretty horrible. In her first video, not only is she infected but her parents have abandoned her. Imagine being a young and sick pre-teen/teenager and having your parents run out the door without even saying goodbye.