That's still unclear, but it's smart to be prepared, says Dr.Nancy Messonnier, a CDC respiratory disease specialist.

美国疾病控制与预防中心(CDC)呼吸道疾病专家南希·梅索尼耶医生说，这一点还不清楚，但做好准备是明智的。

A respiratory disease specialist said they involved otherwise healthy young people who had severe respiratory illnesses and no signs of infection.

呼吸系统疾病的一位专家说，他们的研究对象是患有严重呼吸道疾病且没有感染迹象的健康年轻人。