After following an apparently infected pigeon, House eventually discovers that Joe had an illegal well of rain water on his roof, which was contaminated by
Naegleria fowleri. Foreman came through as it was spraying the plants in the greenhouse and was thus infected. House and Cameron came through hours later after the plants were watered and thus were not exposed. House calls and informs Cameron of this revelation, but Cameron has already performed the biopsy, and both teams have simultaneously discovered the true disease,
primary amoebic meningoencephalitis.