Officials in St. John the Baptist Parish are increasing chlorine levels in the parish’s water system after tests by state health officials confirmed the presence of a rare brain-eating amoeba in one area of the parish’s water lines.

The state Department of Health and Hospitals said tests indicated the single-celled organisms were present in the water lines that service St. John’s Water District No. 1, which includes about 12,500 residents in Garyville, Mount Airy, Reserve and a small part of LaPlace — the area between Acorn and Apricot streets on West Fifth Street.

The amoeba, known as Naegleria fowleri, has been linked to the deaths of three people in Louisiana since 2011. However, no cases of illness related to the most recent confirmation of the amoeba have been reported in St. John or elsewhere, officials said Thursday.

Because Naegleria fowleri cannot be contracted by drinking the water, public health officials said the local water supply remains safe to consume. Most people who contract the disease — a total of 32 nationwide from 2001 to 2010 — did so after swimming in warm, freshwater bodies of water and ingesting contaminated water through their noses. When infections occur, the water containing the amoeba enters the body through the nose and is pushed into the brain.

During a news conference Thursday, St. John Parish President Natalie Robottom said state officials sampled the parish water supply about two weeks ago to check disinfectant levels in the water, and the testing showed lower-than-required levels of chlorine.

The state Health Department issued an emergency rule last year requiring most water systems in Louisiana to maintain a minimum disinfectant level of .5 milligram of disinfectant per liter of water throughout the system. Previous state regulations, dating from 1995, required water systems to have “trace” or “detectable” levels of chlorine.

Robottom said she was notified by state officials of the test results at 3 p.m. Wednesday and immediately began alerting residents.

“The water’s safe to drink. You can bathe in it, you can shower in it, you can cook in it. The concern is that the water goes deep into your nasal passages,” she said.

In light of the test results, the parish needs to raise chlorine levels in the water system for 60 days — a formula that officials say has been successful at eliminating the amoeba elsewhere. At that point, state health officials will test the water again.

St. John is the third parish to test positive for the amoeba in the past two years.

Last year, a 4-year-old boy died after becoming infected with the Naegleria fowleri amoeba, apparently on a Slip’N Slide at a mobile home in St. Bernard Parish. The rare contaminant also was found in treated water in DeSoto Parish in northwest Louisiana. Testing of those water systems this year has not detected the amoeba, officials say.

The three parishes typically used a mix of chlorine and ammonia, called chloramines, as a disinfectant, rather than straight chlorine. That will change in St. John, at least for the next 60 days, officials said.

St. John’s water system was tested as part of a new state testing initiative launched earlier this month. In doing so, state health officials learned the system was not in compliance with the emergency order.

Dr. Jimmy Guidry, the state health department’s medical director, said the state’s taking on the task of testing for the amoeba has been a learning process. There are more than 1,000 water systems in Louisiana that need to be tested, a task that he said could take years to complete.

“There’s not a whole lot of information about the amoeba being in drinking water systems, because we don’t normally look for it,” he said.

Public health experts believe insufficient chlorine levels likely contributed to the presence of the amoeba in parts of the water system in St. Bernard. Last September, state tests showed water supplies in several parts of St. Bernard — including near where the boy is believed to have been infected — had low chlorine levels. The parish then started flushing its water lines with additional chlorine to minimize the threat.

The parish also has been looking into an estimated $21 million effort to replace old, cast-iron waterlines, largely in Arabi and Violet, that have a history of leaking.

Asked whether infrastructure issues may have contributed to the amoeba’s presence in St. John, Robottom said low water pressure wasn’t necessarily the culprit.

“Regardless of whether there are pressure concerns, we have sampling and testing that should detect that,” she said.

Guidry said that as the state testing continues, he expects to find that water systems that have deferred regular maintenance could be at a higher risk of falling below required chlorine levels.

“Water systems around the country have to be maintained,” he said. “As they get older, there’s always a compromise. ... If you lose pressure, if the chlorine dissipates and you have less chlorine, you’re at risk. The chlorine protects you, not just from the amoeba, it protects you from the bacteria.”

Follow Richard Thompson on Twitter, @rthompsonMSY .