The Cordyceps Brain Infection is a central part of The Last of Us franchise, but the details of how the Cordyceps infection started can be easy to miss. The Cordyceps Brain Infection (Cbi) is the fungal infection responsible for wiping out half of society in the world of The Last of Us, resulting in the post-apocalyptic state that the games and show present. Both the original game and sequel provide insight into how it spreads, but players focused on the gameplay can find some of the subtler clues the details can be easy to miss.

In the original The Last of Us, the outbreak initially begins in September 2013. The fungus, spread through a bite from an infected individual or exposure to spores, infects a living individual and transforms them until they become a horrific The Last of Us bloater. Symptoms appear within a couple of days, and then stage two...