The boy, Drake Smith Jr., died from a rare but deadly swelling of the brain caused by Naegleria fowleri, a species of single-celled organism known as an amoeba. (Related: "What We Do—and Don't—Know About Brain-Eating Amoebas.")

The child was playing on a backyard Slip 'n Slide in St. Bernard Parish, near New Orleans, and was apparently infected by amoebae present in the water in early August. About two days later, he was dead.

For N. fowleri to gain access to the brain, it must go up a person's nose and climb the olfactory nerve. Simply drinking water that contains the amoeba is not enough to cause an infection, said Raoult Ratard, Louisiana's state epidemiologist.

"[The boy] spent all day on