Category A infectious substances are defined as those that, upon exposure, are capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals.

• A. They are capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals.
• B. They are capable of causing only minor, non-life-threatening illness.
• C. They are nonpathogenic in humans but pathogenic in animals.
• D. They require only standard packaging and labeling.

Answer: (A)

Category A infectious substances are defined by their potential to cause permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals upon exposure. That high level of risk is what drives the strict handling and packaging requirements. The statement that they can cause such severe outcomes precisely captures why Category A materials demand the most stringent precautions, including specialized packaging and labeling, to prevent exposure during transport and handling. The other descriptions describe far less danger or more routine packaging, which do not meet Category A criteria.