A freshwater amoeba that killed two children swimming near Stillwater a few years ago left an indelible memory for Minnesotans who love water. But now state health officials say that advances in treating the deadly but rare infection make it even more important for swimmers and doctors to understand the symptoms and what to do when faced with them.

The last two confirmed cases of infections caused by Naegleria fowleri in Minnesota occurred in Lily Lake in Stillwater in 2010 and 2012 and resulted in the deaths of children ages 7 and 9, while a suspected case involving a teen swimming in Lake Minnewaska in Glenwood in 2015 turned out to be unrelated.

Though the infection is rare in Minnesota, the amoeba is relatively common, and swimmers should take reasonable precautions at this time of year, said Trisha Robinson, a supervisor at the Minnesota Department of Health.

“There’s always the risk of it being in warm freshwater,” she said, “but it increases as water temperatures increase and water levels decrease — kind of in the dog days of summer.”

The drug miltefosine became commercially available this year for treating the infection, after being deemed experimental and closely controlled in prior years by federal regulators. Used in combination with antibiotics and other treatments, the drug has shown some ability to combat the brain swelling and other symptoms that in the past were almost always fatal.

“That is why it is so important that if anybody shows symptoms [after being in lake water] that they do seek treatment immediately,” Robinson said, even though the classic initial symptoms of headache, fever and vomiting can be due to other conditions.

A May 2017 study in the journal Pediatric Neurology noted that 13 children have now survived their amoebic infections after receiving the medications. However, two children died despite receiving the drug.

Infections from Naegleria fowleri occur when water carrying the amoeba travels up the swimmer’s nose and olfactory nerves to the brain; prevention tips include using nose plugs or plugging your nose when jumping into a lake. The amoeba usually resides in the murky sediment of lake bottoms, so health officials also suggest that swimmers avoid churning up the ground beneath their feet.

The amoeba also thrives in warmer waters, which is why it has been a more common problem in the South.

Health officials nationally were surprised in 2015 by the apparent infection of a teen who had been swimming in Minnewaska — a deeper, colder lake. After the 14-year-old died, an investigation determined that he had suffered a head injury caused by a skateboarding accident that left him vulnerable to more common bacterial meningitis.