Final answer:
Organisms that cause serious illnesses or are lethal are categorized into high biosafety levels, likely BSL-3 or BSL-4, to indicate the level of containment required when working with them in a laboratory setting.
Step-by-step explanation:
Organisms known or suspected to cause serious illness or death belong to a specific biosafety level based on the risk they pose. These levels range from BSL-1, which is for agents not known to consistently cause disease in healthy adults, to BSL-4, which is reserved for the most dangerous agents that pose a high risk of aerosol-transmitted laboratory infections and life-threatening disease. According to the references provided, particularly under the section for emerging diseases and biosafety levels, such organisms would most likely fall under BSL-3 or BSL-4, depending on the nature of the organism and the risk it represents.