Raleigh -The chlorination and filtration systems at an artificial water rapids course where Olympic kayakers train were inadequate to kill a rare, brain-attacking organism, the US Centres for Disease Control and Prevention said after an Ohio teenager died from the amoeba.The rushing water channels at the US National Whitewater Centre had become so murky with debris that the chlorine and ultraviolet light that might have killed the Naegleria fowleri amoeba didn't work, Dr Michael Beach said on Friday."It's kind of a murky water," said Beach, the CDC's associate director for healthy water. Speaking by phone, Beach wouldn't comment on whether a more effective system could have saved the life of Lauren Seitz, 18, of Westerville, Ohio.The centre closed its whitewater rafting and kayaking operations on June 24. The fast-water channels will be drained, dried and scrubbed to kill any vestiges of the amoeba, the non-profit said on its website. The website didn't indicate when the rapids course might reopen. A spokesperson for the centre declined to comment on Friday on the CDC findings.Seitz died on June 19, just three weeks after graduating from high school and more than a week after returning home to suburban Columbus, Ohio, from a church group trip that included a visit to the whitewater centre about 24km west of Charlotte. Her only known underwater exposure was thought to be when her raft overturned at the whitewater centre.The centre held Olympic qualifying trials for US canoe and kayak competitors in April and also hosted the qualifying races before the 2012 and 2008 Olympics, said Aaron Mann, a spokesperson for USA Canoe/Kayak. American Olympians haven't used the Charlotte course in recent weeks because they've been competing in Europe ahead of a training camp in France leading up to the Rio de Janeiro games, he said.The amoeba is very common in lakes and other kinds of warm, fresh water, yet it's very rare that it will make anyone sick, said Dr Thomas Kerkering, chief of infectious diseases cat Virginia Tech Carilion School of Medicine in Roanoke, Virginia. The amoeba won't infect a person who drinks or swallows water containing it, and must enter the body through the nose to cause harm."Where most people get it is when they wipe out waterskiing and the water goes up their nose," Kerkering said.The odds that the organism will cause the dangerous, brain-eating disease are just about chance, Kerkering said, since some people jumping into the water might contract the illness while most others don't.Only 138 people nationwide have been stricken by the disease between 1962 and 2015, according to the CDC. Florida and Texas have had the most cases with 34 each in that time. North Carolina had four cases prior to Seitz, none of them involving the whitewater centre, while Ohio is one of 32 states without a recorded case over the five-decade span. All five cases last year were fatal. They were in California, Oklahoma, Arizona, and two in Texas. The most recent was in Texas last August.Initial symptoms showing up on average five days after exposure may include headache, fever or vomiting and worsen to include stiff neck, confusion, seizures and hallucinations.The deadly amoeba was found in all 11 water samples taken from the National Whitewater Centre's fast-flowing whitewater channel, said Dr Stephen Keener, Mecklenburg County's medical director. Four samples from the neighbouring Catawba River didn't find the organism, but it was found in one sample of the river's sediment, Keener said on Thursday.Water for the centre's courses comes from the Charlotte-Mecklenburg municipal system, two water wells and rain, the operator said.