The Centers for Disease Control and Prevention said a sample from Mohave County tested negative for brain-eating amoeba infection on Wednesday.
County officials said specimens were sent in on Tuesday, and they got the result on Wednesday.
Human infections by brain eating amoebas are very rare in the United States.
Naegleria Fowleri is the scientific name for brain-eating amoeba.
The single-cell parasites are commonly found in fresh-water bodies such as lakes, rivers and hot springs.
Mohave County has had two confirmed cases of brain-eating amoeba infections since 2007, including one last year.
