The temperature in Waco, Texas was approaching 83 degrees last Thursday when Mia Mattioli arrived in search of Naegleria fowleri, a brain-eating, warm-water-loving amoeba that kills almost every person it infects. An environmental engineer at the Centers for Disease Control and Prevention, Mattioli spent the day at BSR Surf Resort, a local water park, filling fifty-liter jugs with samples from the facility's various attractions.