Chapter 3: Prevention
As we studied these bacteria further we realized that at extreme temperatures the microbes that were not in the spore form could be killed. This would mean sterilizing every food source before it could be consumed. The human race could no longer endure on planet Earth. The need had grown too great to get off the planet and begin anew in order to eliminate the bacteria. There was so very little that could be done for those who had been infected, so the surviving humans boarded the ships and took off, leaving Earth behind.
Prevention on the ships was a much simpler issue to tackle. Because of the enclosed space, the life forms, plants and animals could be treated with more care, effectively cleansing the ship of all the bacteria through boiling and signs indicating that Bacterium were not allowed. The ship was also very hygienic, with anti-bacterial soaps and sprays that literally coated the walls.
http://www.zkea.com/images/botulism1.jpg
Since taking flight there has not been any major outbreak of any bacterial infection, especially that of Botulism. On Earth, there was no way to manage the bacteria because of the vast quantities and rate of production, but since the cleansing period our numbers have steadily increased as the living conditions improve.
Excerpts of The History of Earth By Dr. Morgan PhD & Dr. Peter PhD