Minnesota State Department of Health officials have been eyeing a rare parasitic amoeba in the death of child.
The child, whose name, age and sex have not been released, is believed to have died from primary amoebic meningoencephalitis caused by Naegleria fowleri, an amoeba that thrives in warm freshwater.
"Through swimming or diving, it can enter through the nose and gain access to the brain," said Dr. William Schaffner, president of the National Foundation for Infectious Diseases and chairman of preventive medicine at Vanderbilt University Medical Center.
Health officials investigating the death said the child had been swimming at Lily Lake in Stillwater Minn., which has been closed until further notice.
While exceedingly rare, Naegleria fowleri infections are almost always fatal. Only one person out of 123 infected in the United States between 1962 and 2011 has survived, according to the U.S. Centers for Disease Control and Prevention.
"It's also a not easy to diagnose, and it's not easy to treat," said Schaffner, describing how meningitis-like symptoms, such as headache, fever, nausea and stiff neck swiftly give way to confusion, seizures and hallucinations. The infection usually causes death within 12 days, according to the CDC.
In the summer of 2011, Naegleria fowleri killed four people in Virginia, Florida, Kansas and Louisiana, all of whom had been swimming in freshwater lakes.
"The organism seems to multiply better with warmth," said Schaffner, explaining how states with more sustained high temperatures tend to see more cases. "But this year in the Midwest we've had a heat wave and a drought, which makes lakes shallower. Even lakes up in Minnesota are warm."
Minnesota's only previously confirmed case of Naegleria fowleri, in August 2010, was also linked to Lily Lake, according to the Minnesota Department of Health.
But state health department experts said the death should not discourage people from swimming in the state's lakes and rivers.
"The risk of infection from Naegleria in Minnesota is very low," assistant state epidemiologist Richard Danila said in a statement. "Swimming is a very healthy summertime activity and we do not want to discourage people from swimming. Rather, simply avoid swimming, diving or other activities in obviously stagnant water when temperatures are high and water levels are low."