In 1867, the disease seems to have progressed enough that people around him noticed it; Shikanosuke KOJIMA in "Ryoyu jitsuroku" said he contracted it in March; according to Kanefumi NISHIMURA's "Mibu Roshi Shimatsuki", he was seriously ill around September when the quarters were moved to Fudodo Village; and in a letter to Kondo dated October 13, Kojima wrote that he was worried about Okita's worsening condition.
慶応3年（1867年）には周囲が認識し得るほど発病していた模様で、2月頃罹病したとする『両雄実録』（小島鹿之助）、不動堂村へ屯所を移転した9月頃に大病を患ったとする『壬生浪士始末記』（西村兼文）、さらに10月13日付で小島鹿之助が近藤へ送った書簡にも沖田の異常を気遣う文面が見られる。