プログレッシブ和英中辞典(第4版)の解説
びょうせい【病勢】
the state of a disease ⇒ようだい（容体）
翌日病勢が募った
The next day, his condition took a turn for the worse.
その知らせを聞いて彼女の病勢は悪化した
The news aggravated her illness [condition].
病勢は一進一退している
His condition fluctuates between better and worse.