Officials traced the death of a 4-year-old Mississippi boy in August to a day spent playing on a Slip 'n Slide in a New Orleans suburb.
Cause of death: a rare, brain-eating amoeba. At first, officials thought the amoeba, Naegleria fowleri, had been present in muddy water that the boy was playing in on the property. Naegleria fowleri is commonly found in freshwater streams, lakes and rivers.
But testing confirmed last week that the microscopic organism came from the St. Bernard Parish water system that fed the slide. The discovery marks the first time the amoeba has entered a treated water supply in the U.S., said Jonathan Yoder, an epidemiologist with the Centers for Disease Control and Prevention.
The primary risk of disease is when infected water enters the nose, according to the state's Department of Health and Hospitals. Once in the sinus, the amoeba travels along the nerves and crosses into the brain through tiny openings in the bone at the base of the forehead, Yoder said.
Infection by the amoeba, which leads to a form of encephalitis, is rare but almost always deadly.
Federal, state and locals official in St. Bernard Parish — a district with about 40,000 residents southeast of New Orleans — are trying to figure out how the brain-destroying amoeba entered the water supply.
Possible factors include high temperatures along with low levels of chlorine in the water. Tests last week revealed that chlorine was almost undetectable, officials said.
When the amoeba was traced to the parish earlier this month — but had not yet been linked to the water supply — parish officials began flushing their system with chlorine as a precaution. Health officials plan to continue flushing the system for several weeks.
"We know that chlorine kills Naegleria fowleri," said J.T. Lane, assistant secretary for the state public health office, in a statement.
Chlorine levels can be adjusted, but other possible factors are not so easily changed. The amoeba thrives in warmer water, especially hot springs and the lakes and rivers of Southern states. The lingering effects of Hurricane Katrina in 2005 could have exacerbated the water problem, officials said.
The parish's population is two-thirds of its pre-Katrina level, meaning that water cycles less frequently through the pipes. The longer the water sits, the more easily the amoeba can multiply, said Christina Stephens, spokeswoman for the state's Division of Health and Hospitals.
But at this point, the exact cause has not been confirmed.
Local, state and federal agencies continue to test the water, Stephens said. On Friday, parish officials enlisted an expert on water quality from Vanderbilt University to monitor the disinfecting process and water tests.
There have been three deaths in Louisiana from Naegleria fowleri since 2011, state officials said.
And Yoder said the CDC has documented 132 infections from the amoeba since 1962, almost all fatal. This year, there have been four cases.
"When this happens to a family, it's a serious infection. It's a tragedy," Yoder said. "But I do think it's important to put it into perspective."
Ashley Imbraguglio, assistant manager at Parish Seafood and Diner, where the house specialty is Crawfish Monica, isn't taking any chances and is using only boiled or bottled water.
Imbraguglio said customers kept inquiring about the restaurant's water source. Health officials have emphasized that because stomach acid kills the amoeba, tap water is safe to drink. The state issued a detailed article online, aiming to debunk myths about the amoeba.
The CDC has advised residents not to let water get up their noses while bathing or swimming in pools, and it urged swimmers to lower themselves into a pool rather than jump in. Officials told residents to run taps, showers and hoses for five minutes to flush out untreated water before using them. People who flush their sinuses are advised to use water that has been boiled.
The information has done little to ease anxieties in the parish.
"The whole of St. Bernard Parish is panicked right now," said Michelle Rando, 31, a waitress at Gerald's Donuts in the town of Arabi. She said the tap water had a "harsh smell" from the flushing, like it came from a swimming pool.
"I usually drink two to three cups of water while I'm working," Rando said. "I don't touch the water right now."