WOW!!! Best of the series, so far. Continued great descriptions of the environment and physical surroundings such that you have no difficulty envisioning the world Ms. Banner has created. The story flowed smoothly and continues to be full of unexpected twists and turns. Outbreak is the most polished and well put together book in this series. That is why I rated it 4.4. All of the characters have become three dimensional. The chapters continue to be first person, primarily Eli and Harper but occasionally Celdon and Sawyer.
Only one thing nags at me, and has since book 1, the story time line. In all three of the books it is implied that a long period of time has elapsed since Death Storm. However, based on information from all three books, Eli was about 8 or 9 when that occurred and is now in his 20's. This has been nagging at me all along but more since reading Outbreak.
As with the other two previous books, Outbreak ends with a cliff hanger, actually the cliff hanger of all cliff hangers so far! I am running for book 4!