The State Department says the U.S. is working to review whether viral or "other types of attacks" harmed American diplomatic personnel in Cuba.
State Department officials are testifying before the Senate Foreign Relations Committee about the unexplained incidents in Havana.
The hearing comes after The Associated Press reported that a new FBI report shows no evidence for the initial theory of a sonic weapon.
Investigators are considering possibilities including a viral attack.
Officials say the possibility someone deliberately infected people with a virus hasn't been ruled out.