1. the quality or state of being able to spread disease or infection from one person or organism to another
Usage: medical/scientific context
2. the quality of spreading rapidly or being easily transmitted from person to person in a non-medical sense
Usage: figurative use

Examples

• The infectiousness of the virus made it spread quickly through the community.
• Doctors assessed the infectiousness of the disease before recommending quarantine measures.
• The infectiousness of her enthusiasm inspired everyone in the room.
• The high infectiousness of the new variant concerned public health officials.
• His laughter had an infectiousness that made others smile.
• The infectiousness of the catchy song meant it was stuck in everyone's head.
• Scientists studied the infectiousness of the pathogen in laboratory conditions.