patient zero

noun

plural patient zeros also patient zeroes

Definition of patient zero

: a person identified as the first to become infected with an illness or disease in an outbreak The quest to find patient zero, the first person to contract the new virus, has revealed the first known case occurred in Wuhan …— Susan Dunlevy especially : a person documented as being the first known case of a communicable disease in a particular population or region Stay out of hospital emergency rooms unless you are severely ill or injured. For now, it's the likeliest place to catch coronavirus. Anyone unknowingly suffering from coronavirus is likely to go there. That's what "patient zero" in Italy did. — Betsy McCaughey The 26-year-old nurse contracted Ebola after volunteering to care for U.S. 'patient zero' Thomas Eric Duncan, who tragically died on October 10 from the deadly disease. — Ashley Collman et al. — compare index case sense 2