Use 'virulence' to describe how aggressive an illness is, focusing on its capability to cause damage. The virulence of the new strain has put health systems on high alert.
Pro Tip 2/3
Not Contagiousness
Don't confuse 'virulence' with how easily a disease spreads, which is 'contagiousness' or 'infectivity'. Despite its rapid spread, the contagion's virulence remained low.
Pro Tip 3/3
Objective Measure
'Virulence' is often used in a technical or academic sense to express a quantitative measure of harm. Researchers are studying the virulence factors of the bacteria.