noun
person affected by a disease; sufferer; patient
Refers to someone who has contracted or is suffering from a disease, often used in medical, epidemiological, or news contexts. More specific than 患者 (patient), as it emphasizes the fact of being afflicted.
新型コロナウイルスの罹患者数が急増している。
The number of people affected by the novel coronavirus is surging.
この地域ではインフルエンザの罹患者が多く報告さ
Many influenza sufferers were reported in this area.
感染者 refers to an infected person, typically for infectious diseases, and is more common in everyday news. 罹患者 can be used for both infectious and non-infectious diseases, and carries a slightly more formal or written tone.
Compound of 罹患 (りかん, 'contracting a disease') + 者 (しゃ, 'person'). 罹患 is itself from 罹 (り, 'to suffer from') + 患 (かん, 'affliction').