Johnston Atoll is an Atoll in the Pacific Ocean and former home to a US. military base.
In the mid 21st century, Johnston Atoll was home to a quarantine and treatment zone for patients of various illnesses especially Ebola. Apratments were built for the patients, and an area on the far east of the island was sealed off from the sick, to hold the housing for doctors and scientists. (Shadows of Mars)
Long after Ebola was eradicated, Johnston became a temporary evacuation zone during the Martian Revolution. (Seona Logs) Soon after, It became a center to treat those with unique or alien illnesses. (Seona Logs)