A 9-year-old Minnesota boy who died Aug. 7 was infected with the ameba known as Naegleria fowleri, which caused his rare and fatal illness, the CDC has confirmed.

The U.S. Centers for Disease Control and Prevention conducted confirmatory clinical testing for the organism, and reported the results this afternoon to the Minnesota Department of Health.

MDH officials said the cause of the meningitis had been 99 percent certain, but the CDC test results made it 100 percent certain. They said it will never be possible to know for sure where the child was infected, but the timing of the illness and other factors point to Lily Lake in Washington County.

The lake has been closed for the season.

The case was the second in the state in three years. A 7-year-old girl who died of the disease in 2010 also had been swimming in the shallow Stillwater lake.

-- Minnesota Department of Health