Overview
- An eight-year USGS-led study found Naegleria fowleri in 34% of 185 samples from thermally influenced recreational waters, with positives confined to Yellowstone, Grand Teton and Lake Mead.
- Detections included well-known hot and warm sites such as Yellowstone’s Boiling and Firehole rivers, Grand Teton’s Polecat and Granite hot springs, and Lake Mead’s Rogers and Blue Point hot springs.
- Some concentrations were high, with a 2023 Polecat Hot Springs sample at about 116 cells per liter in a country with no U.S. standard, which exceeds France’s 100-cells-per-liter recreational limit.
- The infection is very rare but usually fatal, with CDC records showing 167 U.S. cases since 1962 and only four survivors, and it occurs when warm freshwater enters the nose during swimming or diving.
- The authors call for expanded surveillance and clearer risk communication as warming temperatures help the amoeba spread north, noting most positives came from thermally influenced or low-use sites.