Hot Springs Can Harbor Fatal Parasite

By Carolyn Crist

September 23, 2019

(Reuters Health) - People who swim in hot spring water should do their best to avoid getting water up their nose because it could transmit a deadly parasite, a U.S. case report suggests.

Doctors describe a rare but fatal brain infection caused by a parasitic ameba found in warm freshwater lakes, ponds and hot springs, in the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report, September 13.

"A person cannot get infected by drinking contaminated water (with this ameba), and it is not contagious or spread from person to person," said lead author Dr. Duc Vugia, chief of the California Department of Public Health's Infectious Diseases Branch in Richmond.

The parasite Naegleria fowleri is a single-celled organism found in soil and warm freshwater. It can cause primary amebic meningoencephalitis, or PAM, which is often lethal. In the last 50 years, just 145 U.S. infections have been reported to CDC.

"Infections have also been reported when people irrigate their sinuses using contaminated tap or faucet water," Vugia told Reuters Health by email. "The best ways to reduce the risk of infection include limiting the amount of water going up the nose and using safe water for sinus rinsing."

Vugia and colleagues reported on an October 2018 case of a previously healthy child who was admitted to an intensive care unit at a southern California hospital with headache, vomiting, fever and an altered mental state.

The boy was treated for bacterial and viral meningitis, but then his condition worsened, and he lost consciousness and had respiratory failure. The medical team put him on ventilation, and scans showed swelling in the brain.

Fluid from a spinal tap contained Naegleria amebas, and doctors began treating the boy with miltefosine, an antimicrobial drug used to treat parasitic diseases such as leishmaniasis. However, his condition declined and he died in the hospital on the third day.

An infectious diseases clinician at the hospital contacted the CDC, which notified state and local public health officials.

Family members said that 12 days before the symptoms started, the boy swam in a natural freshwater pool in Inyo County, which is in the Eastern Sierra region of California. Known locally as Hot Ditch, the warm spring stream has several small shallow pools where residents and visitors like to swim. Although the freshwater pools are untreated, swimmers have visited the area for decades without any previous reports of contamination.

The Inyo County Health and Human Services department issued a press release to inform the public about the potential for infection and posted warning signs at each of the Hot Ditch natural pools to alert visitors about the risk.

"Although contracting Naegleria fowleri infection is rare after swimming in hot spring water, the potential risk for this disease should be considered," Vugia said. "People should either refrain from hot spring water-related activities or take actions to prevent spring water from going up the nose."

In 2014, an 11-year-old Florida boy developed fatal PAM after exposure to hot springs in Costa Rica, where N. fowleri was identified, the authors note.

"We've been tracking infections of Naegleria fowleri since 1962, but there is a lot we're still learning about this ameba," said Dr. Jennifer Cope of the CDC in Atlanta, who wasn't involved in the case report.

"It's important that we continue to study Naegleria fowleri to better understand why certain people become infected with the ameba and how infections can be prevented," she told Reuters Health by email.

Typically, the infection occurs when water enters the nose, and the ameba migrates from the nose to the brain along the olfactory nerve. It destroys brain tissue and causes brain swelling, quickly advancing from symptoms to death within five days.

"Hold your nose shut, use nose clips or keep your head above water when taking part in water-related activities in bodies of warm freshwater," Cope said.


MMWR 2019.