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The Last of Us premiere on HBO detailed the start of the Cordyceps brain infection outbreak. On Sept. 26, 2013, the world descended into chaos as the infection reached critical mass. Twenty years later, the mutated fungus is still prevalent in what remains of the post-apocalyptic wasteland. But how did this all begin? Fans of The Last of Us picked up on some clues in the premiere that might have pointed to the origin of the Cordyceps outbreak.

The Cordyceps fungus grows around a person attached to a wall in The Last of Us
Someone infected with the Cordyceps fungus on ‘The Last of Us’ | Liane Hentscher/HBO

Everything to know about the Cordyceps infection in ‘The Last of Us’

First, it’s important to understand exactly what the Cordyceps infection is. As seen in both The Last of Us video games and TV show, the infection is caused by a mutated version of the Cordyceps fungus. The mutation allows the fungus to survive in higher temperatures, thus making humans a viable host. As the show reveals, global warming is what caused the mutation.

The Cordyceps fungus attacks an infected person’s brain and essentially takes over their body. They turn into cannibalistic, extremely violent, zombie-like creatures. There are multiple stages of infection, so infected humans are categorized as Runners, Stalkers, Clickers, and Bloaters.

In the game, a newspaper clipping in Austin, Texas, reveals that the Cordyceps fungus originated on contaminated crops in South America. These crops made it to other parts of the world and infected those who consumed them, causing the outbreak. The brain infection continued to spread via spores in the air and infected people biting others. However, the exact origin of the Cordyceps infection — meaning which crops/foods — was never revealed in The Last of Us, until now.

Fans think contaminated flour is the origin of the Cordyceps infection in ‘The Last of Us’ on HBO

A fan theory on Reddit fills in the missing piece of the puzzle, and it makes a lot of sense. The original poster pointed out that The Last of Us premiere included several hints about contaminated flour being the origin of the Cordyceps outbreak. For starters, Joel (Pedro Pascal) and his daughter, Sarah (Nico Parker), managed to avoid flour at all costs. They didn’t have any flour for pancakes, they turned out the Adlers’ biscuits, and later, the Adlers made cookies, which Sarah didn’t eat.

“There are too many coincidences that have our main characters avoid eating objects with flour,” the Redditor wrote.

Many fans agreed with the theory, even adding more evidence. Joel and Sarah heard on the radio that an outbreak occurred in Jakarta, Indonesia — which contains the largest flour mill in the world. The Last of Us co-creator Craig Mazin also teased on The Last of Us podcast that there were several “breadcrumbs” in the show. Bread? Flour? Very sneaky.

If this is true, then Mrs. Adler was likely infected by the biscuits or cookies. Flour is found in most households and used in many foods, so it could explain other infections, too.

HBO’s ‘The Last of Us’ could detail the origin of Cordyceps

It’s rumored that The Last of Us Episode 2 will head to Jakarta to reveal how the Cordyceps outbreak began, so this theory could be confirmed or debunked soon enough. The episode arrives on Sunday, Jan 22.

New episodes of The Last of Us drop every Sunday at 9 p.m. ET on HBO and HBO Max. Check out the full release schedule for more details.