confirm 的用法：

confirm 是及物动词，宾语可以是名词、代词或that从句。也可以接宾语后，再加以as 短语充当的宾语补足语。

as 短语可以是：

as + 名词

as + 形容词

as + 现在分词 （如果现在分词的动作早于谓语动词，则要用完成体）

as + 过去分词

as + 介词短语

网友的句子是被动语态：主语 + be + confrmed as...

Thirty people have been confirmed as having died while battling a forest fire in southwest China's Sichuan Province,authorities said Monday.

官方周一表示，在扑灭中国西南部四川省发生的森林火灾中，已有30人被确认死亡。