in the past 50 years only three people have survived. most recently 12-year-old caylee hardig who is out of a coma. >> i'm going to take her home some day is amazing. >> reporter: doctors credit it to the experimental drug. the cdc sent the drug to miami to treat zachary and just as friends and family prayed caylee would be the third person to survive this infection, zachary's supporters hope he will be next. >> we can be number four. that's what we're hoping. we're hoping for him to be number four. >> reporter: there are two things you can do to prevent this. when you're swimming, hold your news or use nose clip when is you jump or dive in. and try not to stir up the sediment at the bottom. that's where the amebas live.