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Two recent cases of primary amoebic meningoencephalitis (PAM) show that municipal tap water can harbor the amoeba responsible for the fatal disease, according to CDC researchers.

The deaths of two adults in Louisiana hospitals of infectious meningoencephalitis are the first recorded PAM cases in the country associated with the presence of Naegleria fowleri in household plumbing served by treated municipal water, wrote Jonathan Yoder, MPH, of the CDC's National Center for Emerging and Zoonotic Infectious Diseases in Atlanta, and colleagues in Clinical Infectious Diseases online.

The cases also are the first reports of a potential link between PAM and the use of a nasal irrigation device, the group added. As a result, the CDC recommended that patients who use a neti pot or similar device for nasal irrigation distill, filter, or boil the municipally treated tap water before use.

The authors noted that tap water in the U.S. has not historically been a common source of exposure to N. fowleri, a free-living amoeba commonly found in warm, typically untreated freshwater such as lakes, ponds, and rivers. However, it also can be found in warm groundwater and inadequately treated swimming pools.

PAM symptom onset occurs 1 to 7 days after exposure, and symptoms of infection are similar to bacterial or viral meningitis, including headache, fever, stiff neck, anorexia, vomiting, altered mental state, seizures, and coma.

In the first case, a 28-year-old man abruptly developed symptoms of severe occipital headache radiating down the neck, neck stiffness, back pain, and intermittent vomiting, as well as confusion, fever, and disorientation at admission to the emergency department.

"The patient had chronic allergic sinusitis and irrigated his sinuses with a neti pot at least once daily, using tap water to which he added a commercially available salt packet," the authors explained.

Several amoebae were detected in samples taken from the patient's home, including Hartmannella, Vannella, and Naegleria sp. Water collected from a tankless water heater was polymerase chain reaction (PCR) positive for N. fowleri, although the neti pot was PCR negative for N. fowleri.

In the second case, a 51-year-old woman had presented symptoms over 3 days of altered mental status, nausea, vomiting, poor appetite, listlessness, fatigue, and high fever, as well as neck stiffness and thyromegaly upon examination at an emergency department.

She also had sinus problems and regularly used a neti pot. Water samples from the kitchen faucet, shower, bathtub, and bathroom sink in her home tested positive for N. fowleri.

While no amoebae were cultured from the neti pot, the chance of recovering organisms from a dry neti pot after 2 months was unlikely, the authors pointed out.

Following their deaths, the CDC further investigated the source of the amoebic contamination at the patients' homes and municipal water supplies.

In both cases, municipal water sources tested negative for the amoeba and identification of PAM only occurred after treatment was not effective -- in the first case, the patient was declared brain dead before N. fowleri infection was confirmed, while in the second, identification occurred during the autopsy.

The agency noted that although the salt used in neti pot devices can kill off potential contaminants, the "length of contact time found in real world conditions (<1 minute) would probably not effectively inactivate N. fowleri, which probably requires hours for full inactivation."

They further clarified that the amoebae "were not isolated from the municipal water system in the Louisiana cases; Naegleria sp. were isolated from the premise plumbing, along with other amoebae."

The authors also cautioned that N. fowleri cysts and trophozoites are fairly resistant to chlorine disinfection, but it remains uncertain how the amoeba arrived at the patients' homes and how it was able to colonize the household hot water systems.

They noted that the geographic pattern of this climate-sensitive, thermophilic amoeba seems to be shifting up from the southern U.S., with more cases reported in warm freshwater locations after localized heat waves.

"It is unclear whether the increased temperature and heat waves projected in climate change models will lead to further expansion of the [amoeba's] geographic range," they said.

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