The number of people affected by the novel coronavirus is surging.
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').