The Outbreak occurred in early GSY 11037; it all started when a transport from the outer rim of Castor crashed on the planet Commeri, the transport's crew were infected with a previously unknown virus that was highly infectious and almost always lethal. The outbreak continued to spread as officials tried to contain it but in a matter of months there were eight billion infected beings spread throughout the Twins. The Alliance made efforts to contain it but were hugely unsuccessful, with the outbreak spreading to the core worlds.
Commeri quickly became the epicentre of the outbreak, with an Alliance relief effort in place in an attempt to save the planet and its remaining uninfected inhabitants. The disease became known as the Kyros plague, with the victims called the Kyrosi; they were so-named because they become irrational and violent (the old standard word for rage was Kyros). The plague took 34 standard hours to take hold and fully infect the host. There is currently no known cure.
The disease had two forms, one affected one in five hundred beings, that had an incubation period of 48 hours, after which causing the host to explode, spreading spores around the immediate area, infecting many quickly. The other form took half as long to incubate, but could only be spread by direct contact, making it less of a hassle to contain.
Entire planets were placed under quarantine during the Outbreak.