Ellie and Joel, her father figure, we're exploring an abandoned building for supplies, but there was spores do they had to put on their masks.

Ellie didn't really need hers since she was immune, but it was in case they happened to see someone.

While on their exploration, they hear heavy breathing and coughing, so naturally Ellie goes behind Joel and as they enter a room, they see a girl struggling to breath because of the spores

Ellie: "Who are you? Are you okay?"