Stillwater residents peppered the mayor and three public health officials with questions Monday night about how two Stillwater children who swam in Lily Lake died two years apart of a rare brain infection.

The officials said the rare odds-defying scenario -- only 10 cases of primary amoebic meningoencephalitis have been reported nationwide in a decade -- left them searching for answers. The illness, a form of meningitis, killed 9-year-old Jack Ariola Erenberg on Aug. 7 and 7-year-old Annie Elizabeth Bahneman two years ago.

Both swam in Lily Lake before rapidly falling sick. Only one person out of 123 known infected persons in the United States from 1962 to 2011 has survived, the national Centers for Disease Control has said.

In the town hall meeting hosted by Rep. Kathy Lohmer, R-Lake Elmo, many of the written questions from the audience asked about the biology of the amoeba parasite. But an angry Stillwater resident, Lisa Nelson, confronted Mayor Ken Harycki over why the city hadn't closed the Lily Lake swimming beach after Annie's death in 2010.

"There is absolutely no reason this little boy should have died, who everybody loved so much," Nelson said. "You did him wrong; that's what I'm here to say."

Nelson persisted in her criticism of the mayor until Jack's mother, in tears, begged her to stop.

Harycki defended the city, saying the lake was closed to swimmers within 40 minutes of receiving notification of Jack's death. Neighbors were alerted and other measures were taken, he said.

"We hope to meet shortly with officials to see what the process should be going forward," said the mayor, who didn't address allegations that the city should have closed the beach after Annie's death. But he said he would work to find answers. "I think we did everything humanly possible to get the word out that night."

Annie's mother, Bridget Bahneman, said after the meeting that she favored closing the lake and had proposed it after her daughter's death. She said, however, that nobody should think that closing Lily Lake means other lakes are safe. "What I want is for people not to feel a false sense of security if they swim at another lake," she said.

Health officials confirmed the link with Lily Lake after testing her daughter's brain and her spinal fluid, she said.

Many Minnesota lakes have the parasite and it can come and go, said Jim Koppel, deputy commissioner at the Minnesota Department of Health. "It's not something that's quickly detectable and it's not something that's going to be consistent."

Jack had fallen ill and become dizzy while camping with his mother and other family members in the Grand Marais area, on the North Shore of Lake Superior. At first, the doctors thought it was flu, and Jack returned to camp. He became sicker, with a bad headache, and a medical helicopter flew the boy from Grand Marais to Duluth, where he died. Jack was to have begun fourth grade this year at Lily Lake Elementary in Stillwater.

Annie's death was the first in Minnesota from the meningitis and probably the first in a Northern state, the MHD said. She died at Children's Hospital in St. Paul four days after she fell sick with vomiting and a headache.

Infections are caused when water enters the nose, enabling the one-celled organism to crawl into the brain. The amoeba thrives in warm water and proliferates in prolonged heat waves. Most of cases have been in Southern states.

Lily Lake's beach has been closed for the rest of the warm-weather season. Over the winter, health officials will decide what needs to be done regarding public safety.

Koppel and county health manager Lowell Johnson said Monday night that they would work to determine a public policy and consider how to issue precautions.

Kevin Giles • 651-925-5037 Twitter: @stribgiles