patient zero
noun
plural patient zeros also patient zeroes
: 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. … 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
Cite this Entry
“Patient zero.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/patient%20zero. Accessed 7 Jul. 2026.
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