noun
person who tested negative
Used in medical or public-health contexts for someone whose test result (e.g., PCR, antigen) is negative for a target infection.
PCR検査で陰性者と判定された人は、隔離を解除されます。
People who are determined to be negative by PCR test will be released from quarantine.
陰性者でも、引き続き感染予防に努めてください。
Even if you tested negative, please continue to take precautions against infection.
陰性 is the noun/adjective meaning 'negative (test result)', while 陰性者 specifically refers to the person.
Compound of 陰性 (negative, from medical testing terminology) and 者 (person).