Updated March 7, 2025
NCCID Disease Debriefs provide Canadian public health practitioners and clinicians with up-to-date reviews of essential information on prominent infectious diseases for Canadian public health practice. While not a formal literature review, information is gathered from key sources including the Public Health Agency of Canada (PHAC), the USA Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and peer-reviewed literature.
This disease debrief was prepared and updated by NCCID. Questions, comments, and suggestions regarding this disease brief are most welcome and can be sent to nccid@manitoba.ca
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Questions Addressed in this debrief:
- What are important characteristics of Naegleria fowleri?
- What is happening with current outbreaks of Naegleria fowleri?
- What is the current risk for Canadians from Naegleria fowleri?
- What measures should be taken for a suspected Naegleria fowleri case or contact?
What are important characteristics of Naegleria fowleri?
Cause
Naegleria fowleri is a type of single-celled organism called a free-living amoeba. It lives in soil and warm freshwater and is distributed worldwide, including in the United States, Australia, New Zealand, Europe, Latin America, Asia, and Africa. Naegleria fowleri is generally harmless to humans but can cause a deadly infection called primary amoebic meningoencephalitis (PAM) if it reaches the brain. Due to this illness, it is colloquially called the “brain-eating amoeba.” PAM can happen when water containing Naegleria fowleri enters the nose forcefully. Once in the sinus passages, the amoeba travels to the brain, where it causes damage and swelling, leading to death in 97% of cases.
PAM is very rare, with less than 10 people diagnosed per year in the United States (U.S.). Cases of PAM from Naegleria fowleri infection have also been reported in Australia, New Zealand, Europe, Latin America, Asia, and Africa. No one has ever been documented to have contracted PAM in Canada.
Naegleria fowleri can live in tropical and subtropical climates all year; it is mainly found in temperate regions during the warmer summer months. The amoeba lives in soil and warm freshwater, surviving best at temperatures between 25-40 degrees Celsius. It can survive in near freezing temperatures and for short periods above 50 to 60 degrees Celsius. The life cycle of the amoeba has three forms: cysts, trophozoites, and flagellates. It can switch between these forms to adapt to different environmental conditions, with cysts able to survive more extreme temperatures and adverse conditions.
Naegleria fowleri is commonly found in natural freshwater, including lakes, ponds, streams, rivers, and hot springs. It can also be found in water reservoirs, tap water, water heaters, warm waters emitted from factories or power plants, and inadequately chlorinated recreational facilities such as pools, splash pads, and surf parks. It is not found in saltwater or properly chlorinated pools and recreation facilities.
Most PAM cases have occurred in people soon after they have gone swimming, diving, or engaged in other recreational activities in freshwater, such as in lakes, ponds, or rivers. In the U.S., most cases have occurred during the summer, when warmer water temperatures create ideal conditions for Naegleria fowleri. Less frequently, people have contracted Naegleria fowleri infections from using improperly disinfected swimming facilities, such as splash pads, surf parks, and pools. There have also been some cases of people acquiring PAM from tap water contaminated with Naegleria fowleri while bathing and from using non-sterilized tap water to rinse their sinuses.
Although the risk of PAM is very low, it is of public health importance due to its high mortality rate. Additionally, public health measures such as public education, proper maintenance of recreational facilities, and controlling pathogens in public water systems can help to reduce the risk of contracting PAM.
Health Canada: Guidelines for Canadian Recreational Water Quality Guideline Technical Document – Microbiological Pathogens and Biological Hazards
CDC: About Naegleria fowleri Infections
CDC: What Causes Naegleria fowleri Infection
NIH: Naegleria
Current Opinion in Infectious Diseases: Amebic encephalitis and meningoencephalitis: An update on epidemiology, diagnostic methods, and treatment
Signs and Symptoms
According to the U.S. Centers for Disease Control and Prevention (CDC), people with PAM typically first experience symptoms between 1 and 12 days after exposure, with a usual onset of 5 days. Initial symptoms may include headache, fever, nausea, and vomiting. The disease progresses quickly after initial symptoms begin. As the disease worsens, symptoms may include stiff neck, confusion, hallucinations, inattention, and seizures, normally followed by coma and death. People with PAM usually die within 5 days of symptoms first appearing, but death can occur between 1 and 18 days after symptoms start.
CDC: Symptoms of Naegleria fowleri Infection
NIH: Naegleria
Severity and Complications
PAM occurs when water containing Naegleria fowleri goes far up the nose into the nasal passages. The amoeba then passes through the mucosal layer, following the olfactory nerve into the brain. Naegleria fowleri causes disease by damaging brain tissue and causing inflammation, normally leading to coma and death. PAM is typically fatal even with treatment, with a case fatality rate of over 97%. Most people who have died from PAM had otherwise been in good health.
PHAC: Pathogen Safety Data Sheets: Infectious Substances – Naegleria fowleri
Health Canada: Guidance On Waterborne Pathogens in Drinking Water
CDC: About Naegleria fowleri Infections
NIH: Naegleria
Epidemiology
Naegleria fowleri infections are very uncommon. Researchers from the CDC estimate there have been 381 reported cases of PAM worldwide as of 2018. The highest numbers of reported cases were in the U.S. (41%), Pakistan (11%), Mexico (9%), India (7%), and Australia (7%). Among reported cases, 182 were laboratory-confirmed, with only seven confirmed survivors. Most laboratory-confirmed cases of Naegleria fowleri infection have occurred in the United States. From 1962-2023, there have been 164 cases of PAM in the U.S., including four survivors. However, the incidence of PAM is very low, at less than 10 documented cases per year in the U.S.
Cases in the United States have mainly occurred during the summer and were usually linked to recreational activities in warm freshwater, most commonly lakes, ponds, and reservoirs, with exposures from rivers and streams being less common. PAM also primarily occurs in children and young adults, who tend to be male. Boys may have more behavioural risk factors for contracting PAM, such as diving or playing in sediment in the water. The exact reason for more young boys being affected by PAM is unknown.
Most cases of PAM in the U.S. have occurred in the South, primarily in Texas, Florida, and southern California. However, in recent years, people have also acquired PAM in more northern states such as Kansas, Iowa, Nebraska, Maryland, Minnesota, Indiana, and northern California. This change in geographic exposure locations may be related to climate change, since warmer temperatures can cause warmer freshwater conditions that support Naegleria fowleri’s growth.
CDC: About Naegleria fowleri Infections
CDC: What Causes Naegleria fowleri Infection
Clinical Infectious Diseases: Epidemiology and Clinical Characteristics of Primary Amebic Meningoencephalitis Caused by Naegleria fowleri: A Global Review
Current Opinion in Infectious Diseases: Amebic encephalitis and meningoencephalitis: An update on epidemiology, diagnostic methods, and treatment
Emerging Infectious Diseases: Geographic Range of Recreational Water–Associated Primary Amebic Meningoencephalitis, United States, 1978–2018
Laboratory Diagnosis
PAM is difficult to diagnose because it is very uncommon and presents with symptoms similar to those of bacterial meningitis. Due to its quick progression and high mortality rate, the disease is frequently diagnosed after the patient has died. According to the U.S. National Institutes of Health (NIH), health practitioners should suspect PAM if a patient has meningoencephalitis or meningitis and had recent contact with freshwater.
PAM is diagnosed with special laboratory tests. These are only available in some labs, such as the CDC’s Free-Living and Intestinal Amebas (FLIA) Lab in the U.S. The tests include polymerase chain reaction to identify the amoeba in tissue or cerebrospinal fluid (CSF); tests to look for antibodies to Naegleria fowleri, such as immunohistochemical testing and indirect immunofluorescent staining; and visual identification of the amoeba in CSF samples using a microscope.
CDC: Clinical and Laboratory Diagnosis for Naegleria fowleri Infection
NIH: Naegleria
Transmission
Naegleria fowleri infections are transmitted to humans when contaminated water forcefully goes up the nose, which can happen from swimming or diving in warm lakes, rivers, or ponds. People have also been infected with Naegleria fowleriat recreational swimming facilities that were not adequately maintained or disinfected. Using water containing Naegleriafowleri to rinse the sinuses, including using neti pots, can also transmit the amoebas.
Once in the sinus passages, Naegleria fowleri moves up the olfactory nerve and through the cribriform plate into the brain, where it causes primary amebic meningoencephalitis (PAM). The quantity of Naegleria fowleri needed to cause an infection is unknown.
People cannot contract PAM from:
- Ingesting water containing Naegleria fowleri
- Swimming in pools that are properly chlorinated
- Close contact with people or animals infected with Naegleria fowleri
Health Canada: Guidance On Waterborne Pathogens in Drinking Water
CDC: About Naegleria fowleri Infections
CDC: What Causes Naegleria fowleri Infection
NIH: Naegleria
Prevention and Control
Prevention Measures
The CDC recommends that people take precautions to reduce the risk of Naegleria fowleri infections any time they go into warm freshwater, including lakes, ponds, hot springs, rivers, and streams. Specifically, people are advised to:
- Avoid swimming and other activities in freshwater during the hotter summer months when water temperatures are warmer
- Hold their nose closed or wear a nose clip when jumping or diving into water
- Keep their head out of the water in hot springs and geothermal pools
- Avoid disturbing the soil or sediment at the bottom of freshwater bodies
To prevent Naegleria fowleri infection when rinsing their sinuses, people should always:
- Use water bought from the store that says “distilled” or “sterile” on the packaging or
- Use tap water that has been boiled for at least one minute (3 minutes at altitudes above 6,500 feet), then allowed to cool
A few cases of PAM have been linked to public tap water in the U.S., Australia, and Pakistan.
The CDC recommends taking steps to prevent water from entering the nose when public water systems have been contaminated with Naegleria fowleri. They advise people to:
- Prevent water from going up their nose when taking a bath, showering, and washing their face.
- Keep their head above water and prevent water from going up the nose when using small plastic or inflatable pools. Thoroughly clean small pools and allow them to dry after use.
- Run taps for 5 minutes before using, especially right after water utilities have increased disinfectant levels.
- Supervise children if they play with sprinklers or hoses to stop them from spraying water up their noses. Avoid using slip and slides and water activities that can spray water up the nose.
- Keep swimming pools adequately chlorinated.
- Only use sterile, distilled, or boiled water to rinse or cleanse their sinuses.
Control Measures
Recommended control measures depend on the source of exposure. If Naegleria fowleri has been found in public water systems, utilities may briefly increase disinfectant levels. This helps kill the amoeba and dislodge layers of film in pipes where they can grow.
Pools, splash pads, surf parks, and other recreational facilities should be well maintained with adequate chlorine levels to prevent Naegleria fowleri infections. People cannot get PAM from properly maintained recreational facilities.
The CDC does not recommend taking measures to address Naegleria fowleri levels in natural freshwater bodies, such as testing the water or placing warning signs. There are no standard testing procedures for identifying and estimating quantities of Naegleria fowleri in freshwater bodies. Additionally, it does not recommend placing warning signs for Naegleria fowleri since this may give the false impression that lakes and recreational water bodies without signs do not contain the amoeba.
CDC: How to Prevent Naegleria fowleri Infection
CDC: About How to Safely Rinse Sinuses
CDC: How to Prevent Naegleria fowleri Infection When Swimming
CDC: Naegleria fowleri and Public Water Systems
Vaccination
There is no vaccine to protect against Naegleria fowleri infection.
PHAC: Pathogen Safety Data Sheets: Infectious Substances – Naegleria fowleri
Health Canada: Guidance On Waterborne Pathogens in Drinking Water
Treatment
While Naegleria fowleri infection is usually fatal, patients can sometimes survive if diagnosed and treated quickly. The CDC recommends treating PAM using combinations of antimicrobial medications. Treatment usually includes administering conventional amphotericin B in combination with other medications such as miltefosine, azoles medications (for example, fluconazole or voriconazole), azithromycin, rifampin, and dexamethasone. A new investigational drug called Nitroxoline may also be beneficial for treating PAM and is available through the CDC.
In addition to medication, controlled hypothermia has been used on two patients who survived and regained normal neurological functioning after recovering.
CDC: Clinical Care of Naegleria fowleri Infection
NIH: Naegleria
Current Opinion in Infectious Diseases: Amebic encephalitis and meningoencephalitis: An update on epidemiology, diagnostic methods, and treatment
What is happening with current outbreaks of Naegleria fowleri infection?
Naegleria fowleri infections occur infrequently and do not cause outbreaks. The incidence of Naegleria fowleri infections in the U.S. has been consistent from 1978-2018, at less than 10 cases per year.
Recent cases include three children in the southern U.S. who died of PAM after being exposed at inadequately chlorinated splash pads. Two cases occurred in Texas, in September 2020 and September 2021, and one in Arkansas in September 2023.
In 2022, there were at least three fatal cases of PAM in Nebraska, Iowa, and Arizona, resulting from suspected exposures swimming at a river and two lakes respectively. In another possible case, a teenage boy in Florida diagnosed with PAM survived after treatment with antimicrobials and induced hypothermia. However, that case was not confirmed by the laboratory tests.
In 2023, there were at least two additional cases of PAM, which were both fatal. In February 2023 in Florida, a man contracted PAM and died after rinsing his sinuses with tap water, representing the first U.S. case linked to tap water. Another person died of PAM in Georgia after a likely exposure at either a lake or pond.
CDC: What Causes Naegleria fowleri Infection
CDC: Operating and Managing Public Pools, Hot Tubs and Splash Pads
CNN: A brain-eating amoeba claims the life of a 6-year-old boy in Texas
AP News: Boy dies from brain-eating amoeba found at Texas splash pad
CNN: An Arkansas toddler dies of rare brain-eating amoeba infection likely contracted at splash pad
Nebraska Department of Health and Human Services: DHHS Reports First Suspected Death from Naegleria fowleri Infection
ABC News: Missouri swimmer dies of rare brain-eating amoeba
CNN: Boy dies from rare brain-eating amoeba that may have been contracted at Lake Mead
NBC 6 South Florida: Florida teenager survives brain-eating amoeba with 97% fatality rate
Newsweek: Man dies from brain-eating amoeba found in tap water
Georgia Department of Public Health: Georgia resident dies from rare brain infection-Naegleria Fowleri
Emerging Infectious Diseases: Geographic Range of Recreational Water–Associated Primary Amebic Meningoencephalitis, United States, 1978–2018
Current Opinion in Infectious Diseases: Amebic encephalitis and meningoencephalitis: An update on epidemiology, diagnostic methods, and treatment
What is the current risk for Canadians from Naegleria fowleri?
There has never been a recorded case of PAM acquired in Canada. According to Health Canada, there is little risk of contracting PAM in Canada. However, they note that increasing temperatures due to climate change could extend the geographic range of Naegleria fowleri into Canadian freshwaters.
Health Canada has also determined that Naegleria fowleri is not an immediate risk for Canadian drinking water systems. Despite this, they advise Canadian residents to always use distilled or boiled water when rinsing or cleansing the sinuses to prevent infection with Naegleria fowleri and other pathogens.
Health Canada: Guidelines for Canadian Recreational Water Quality Guideline Technical Document – Microbiological Pathogens and Biological Hazards
Health Canada: Guidance On Waterborne Pathogens in Drinking Water
What measures should be taken for a suspected PAM case or contact?
PAM caused by Naegleria fowleri is not a nationally notifiable disease in Canada. Naegleria fowleri infection cannot spread from person to person, so there is no risk to close contacts of people diagnosed with PAM.
Anyone who develops symptoms such as headache, fever, vomiting, and stiff neck should urgently seek medical attention and let health providers know if they have had any recent freshwater exposures.
For health professionals who suspect a patient has PAM, the CDC recommends contacting their Emergency Operations Center, which can assist with diagnosis, testing, and treatment. The Centre can be reached directly by U.S. clinicians or clinicians outside the U.S. through their Ministry of Health.
PHAC: Case definitions: Nationally notifiable diseases
CDC: About Naegleria fowleri Infections
CDC: Clinical Care of Naegleria fowleri Infection
CDC: About CDC’s Naegleria fowleri Program
Clinical Infectious Diseases: Epidemiology and Clinical Characteristics of Primary Amebic Meningoencephalitis Caused by Naegleria fowleri: A Global Review