An expression meaning 'is considered to …' or 'is regarded as …'; commonly used in written language to indicate judgment, estimation, or reported opinion.
この病気は珍しいとされるが、実際の患者数は増えている。
This illness is considered rare, but the actual number of patients is increasing.
その建物は文化財に指定されているか、少なくとも重要な遺構とされる。
That building is designated as a cultural property, or at least is regarded as an important relic.
彼はプロジェクト成功の立役者だとされる。
He is regarded as the person who made the project successful.