What is Naegleria?

Naegleria is a free-living ameba (a single-celled living organism). It is so small that it can only be seen with a microscope. It is commonly found in warm fresh water (such as lakes, rivers, and hot springs) and soil. Only one species of Naegleria infects people: Naegleria fowleri.

How does Naegleria fowleri infect people?

Naegleria fowleri infects people when water containing the ameba enters the body through the nose. This typically happens when people go swimming, diving, or when they put their heads under fresh water, like in lakes and rivers. The ameba then travels up the nose to the brain, where it destroys the brain tissue and causes a devastating infection called primary amebic meningoencephalitis (PAM). PAM is almost always fatal.

Naegleria fowleri infections may also happen when people use contaminated tap water to cleanse their noses during religious practices or rinse their sinuses (sending water up the nose).

In very rare instances, people have gotten Naegleria fowleri infections from recreational water that didn’t have enough chlorine in it, such as pools, splash pads, or surf parks.

There is no evidence that Naegleria fowleri can spread through water vapor or aerosol droplets (such as shower mist or vapor from a humidifier).

People cannot be infected with Naegleria fowleri by drinking contaminated water.

Where is Naegleria fowleri found?

Naegleria fowleri lives in warm fresh water and soil around the world. The amebae may be present in any freshwater body in the United States, regardless of the state, especially during the warmer months of July, August, and September.

Naegleria fowleri is a heat-loving (thermophilic) organism, meaning it thrives in heat and likes warm water. It grows best at high temperatures up to 115°F (46°C) and can survive for short periods at even higher temperatures. Scientists have tested water temperatures from lakes and rivers linked to some PAM cases, and the temperatures have typically been higher than 80°F. However, it is possible that the amebae may live in water with a temperature below 80°F.

The ameba can be found in:

• Warm fresh water, such as lakes and rivers
• Geothermal (naturally hot) water, such as hot springs
• Warm water discharge from industrial or power plants
• Untreated geothermal (naturally hot) drinking water sources
• Swimming pools, splash pads, surf parks, or other recreational venues that are poorly maintained or don’t have enough chlorine in them
• Tap water
• Water heaters
• Soil, including sediment at the bottom of lakes, ponds, and rivers

Naegleria fowleri is not found in salt water, like the ocean.

In what water temperature does Naegleria fowleri cause infection?

Naegleria fowleri is a heat-loving (thermophilic) organism, meaning it thrives in heat and likes warm water. It grows best at high temperatures up to 115°F (46°C) and can survive for short periods at even higher temperatures. Scientists have tested water temperatures from lakes and rivers linked to some PAM cases, and these temperatures have typically been higher than 80°F. However, it is possible that the amebae may live in water with a temperature below 80°F. It is less likely to be found in the water as temperatures decline. But the ameba can be found in lake or river sediment at temperatures well below where one would find the ameba in the water.

What is the source of food for Naegleria fowleri?

Naegleria fowleri eats other small organisms like bacteria found in the sediment in lakes and rivers.

Can I get a Naegleria fowleri infection from a properly disinfected swimming pool?

No. You cannot get a Naegleria fowleri infection from a properly cleaned, maintained, and disinfected swimming pool.

In very rare instances, Naegleria fowleri has been found in swimming pools, splash pads, surf parks, or other recreational venues that are poorly maintained or don’t have enough chlorine in them.

How common are Naegleria fowleri infections in the United States?

Naegleria fowleri infections are rare.* In the United States, between zero and five cases were diagnosed annually from 2012 to 2021. During this period, a total of 31 infections were reported in the United States. Of those cases, 28 people were infected by exposure to recreational water, two people were infected after rinsing their sinuses using contaminated tap water, and one person was infected by contaminated tap water used on a backyard slip-n-slide.

Most Naegleria fowleri infections happen in young males, especially those 14 years old and younger. The reasons for this aren’t clear. It’s possible that young boys are more likely than others to participate in activities such as diving into the water and playing in the sediment at the bottom of lakes and rivers.

*Rare Disease
There is no universal definition of a “rare disease,” but the U.S. Rare Disease Act of 2002 defined a rare disease as a disease that affects fewer than 200,000 people in the United States. This definition has been adopted by the National Institutes of Health, Genetic and Rare Diseases Information Centers.

When do Naegleria fowleri infections most commonly happen?

Infections usually happen when temperatures are hot, which results in higher water temperatures and lower water levels.

While infections with Naegleria fowleri are rare, they happen mainly during the summer months of July, August, and September.

Can infection be spread from one person to another?

No. Naegleria fowleri infection cannot be spread from one person to another.

What are the symptoms of Naegleria fowleri infection?

Naegleria fowleri causes PAM, a brain infection that destroys brain tissue. In its early stages, symptoms of PAM may be similar to symptoms of bacterial meningitis.

The first symptoms of PAM usually start about 5 days after infection, but they can start within 1 to 12 days. Symptoms may include headache, fever, nausea, or vomiting. Later symptoms can include stiff neck, confusion, lack of attention to people and surroundings, seizures, hallucinations, and coma. After symptoms start, the disease progresses rapidly and usually causes death within about 5 days (but death can happen within 1 to 18 days).

What is the cause of death from Naegleria fowleri infection?

The infection destroys brain tissue, causing brain swelling and death.

What is the death rate for an infected person who begins to show signs and symptoms?

The death rate is over 97%. Only four people have survived out of 154 known infected individuals in the United States from 1962 to 2021.

Is there effective treatment for infection with Naegleria fowleri?

Because PAM is so rare, and because the infection progresses so quickly, effective treatments have been challenging to identify. There is some evidence that certain drugs may be effective, but we are still learning about the best drugs to treat these infections. Currently, PAM is treated with a combination of drugs, often including amphotericin B, azithromycin, fluconazole, rifampin, miltefosine, and dexamethasone. These drugs are used because they are thought to be effective against Naegleria fowleri and have been used to treat patients who survived. Miltefosine is the newest of these drugs. It has been shown to kill Naegleria fowleri in the laboratory and has been used to treat three survivors.

What should I do if I have been swimming or playing in fresh water and think I have symptoms of PAM?

Infection with PAM is rare. The early symptoms of PAM are similar to those caused by other more common illnesses, such as bacterial meningitis. People should seek medical care immediately whenever they develop a sudden onset of fever, headache, vomiting, or stiff neck, particularly if they have been in warm fresh water recently.

How common is Naegleria fowleri in the environment?

Naegleria fowleri occurs naturally in freshwater bodies, such as lakes, rivers, and hot springs, and in soil. The amebae are more likely to live in sediment at the bottom of lakes, ponds, and rivers, so people should avoid digging in, or stirring up the sediment in shallow, warm fresh water. Though the risk is low, people should always assume there is a risk for infection whenever entering warm fresh water.

In the United States, most infections have been linked to swimming in southern states, like Florida and Texas. However, the geographical areas where Naegleria fowleri infections happen in the United States are changing. Evidence suggests that the range of Naegleria fowleri is expanding northward, which is possibly a result of climate change and warmer temperatures.

In very rare instances, Naegleria fowleri has been found in swimming pools, splash pads, surf parks, or other recreational venues that are poorly maintained or don’t have enough chlorine in them.

Will Naegleria fowleri infections become more common because of climate change?

It is possible that Naegleria fowleri infections will become more common because of climate change. This heat-loving ameba thrives in warm fresh water such as lakes, rivers, and hot springs. Most infections in the United States have happened in southern states, but cases have been reported in more northern states in recent years. Climate change may be a contributing factor. As air temperatures rise, water temperatures in lakes and ponds also rise and water levels may be lower. These conditions provide a more favorable environment for the ameba to grow. Heat waves, when air and water temperatures may be higher than usual, may also allow the amebae to thrive.

Since 2010, cases have been confirmed in more northern states such as Nebraska, Iowa, Minnesota, Indiana, Maryland, and northern California, which suggests a northward expansion of cases.

Naegleria fowleri may be present in any freshwater body in the United States, regardless of the state, especially during the warmer months of July, August, and September.

Is there a routine and rapid test for Naegleria fowleri in the water?

No. It can take weeks to perform an environmental investigation and identify the ameba in water. Previous water testing has shown that Naegleria fowleri is commonly found in freshwater bodies. Though the risk is low, recreational water users should always assume there is a risk for infection whenever entering warm fresh water.

How does the risk of Naegleria fowleri infection compare with other water-related risks?

The risk of Naegleria fowleri infection is very low. There were 31 reported infections in the United States in the 10 years from 2012 to 2021, despite millions of recreational water exposures each year. By comparison, in the 10 years from 2010 to 2019, there were an estimated 3,957 unintentional drowning deaths each year in the United States.

What swimming behaviors have been associated with Naegleria fowleri infection?

Behaviors associated with the infection include diving or jumping into the water, putting the head under water, or engaging in other activities that cause water to go up the nose. Since the amebae are more likely to live in the sediment at the bottom of lakes, ponds, or rivers, swimmers should also avoid digging or stirring up the sediment.

Most Naegleria fowleri infections happen in young males, especially those 14 years old and younger. The reasons for this aren’t clear. It’s possible that young boys are more likely to participate in activities such as diving into the water and playing in the sediment at the bottom of lakes and rivers.

How will the public know if a lake or other water body has Naegleria fowleri?

Naegleria fowleri is naturally occurring in fresh water. People should always assume that Naegleria fowleri is present in warm freshwater lakes, rivers, and hot springs across the United States. Posting signs based on finding Naegleria fowleri in the water is unlikely to be an effective way to prevent infections. This is because:

• Naegleria fowleri commonly occurs in water, but infections are rare.
• The relationship between finding Naegleria fowleri in the water and people getting infected is unclear.
• The location and number of amebae in the water can vary over time within the same lake or river.
• There are no rapid, standardized testing methods to detect and measure the amount of Naegleria fowleri in water.
• Posting signs might create misconceptions:
  • People might think that a body of water without signs is free from Naegleria fowleri.
  • People might think that if a sign is posted near one part of a water body, other parts without signs are free of Naegleria fowleri.

How can I prevent infection with Naegleria fowleri?

Naegleria fowleri infects people when water containing the ameba enters the body through the nose. Infection is rare and typically happens when people go swimming, diving, or put their heads under water in warm freshwater places, like lakes and rivers. Very rarely, infections have been reported when people cleanse their noses during religious practices or rinse their sinuses (nose) using contaminated tap water. Naegleria fowleri can grow in pipes, hot water heaters, and water systems, including treated public drinking water systems.

Personal actions to reduce the risk of Naegleria fowleri infection should focus on preventing water from going up the nose.

This information is not meant to be used for self-diagnosis or as a substitute for talking to a health care provider. If you have any questions about the amebae described above or think that you may be infected, talk to a health care provider immediately.

Naegleria fowleri is a heat-loving (thermophilic), free-living ameba (single-celled microbe), commonly found around the world in warm fresh water (like lakes, rivers, and hot springs) and soil. Naegleria fowleri is the only species of Naegleria known to infect people. Most of the time, Naegleria fowleri lives in freshwater habitats by feeding on bacteria. However, in rare instances, the ameba can infect humans by entering the nose during water-related activities. Once in the nose, the ameba travels to the brain and causes a severe brain infection called primary amebic meningoencephalitis (PAM), which is usually fatal.

History

The first report identifying PAM infections was published in 1965 in Australia. The report identified three fatal infections from 1965 and one from 1961. The ameba that caused the infections was identified as a new species, which was later named Naegleria fowleri after one of the authors of the original report, M. Fowler. A 1966 report was the first to identify infections in the United States, which occurred in 1962 in Florida. Later investigations using archived autopsy tissue samples identified PAM infections that had occurred in Virginia as early as 1937.

Life Cycle

Naegleria fowleri has three stages in its life cycle: cysts (1), trophozoites (2), and flagellated forms (3). The trophozoites replicate by promitosis (nuclear membrane remains intact) (4). Naegleria fowleri is found in fresh water, soil, thermal discharges of power plants, geothermal wells, and poorly chlorinated recreational and tap water. Trophozoites can turn into temporary non-feeding flagellated forms which usually revert back to the trophozoite stage. Trophozoites infect humans or animals by penetrating the nasal mucosa, usually during swimming or sinus irrigation (5), and migrating to the brain (6) via the olfactory nerves causing PAM. Naegleria fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue, while flagellated forms are occasionally found in CSF. Cysts are not seen in brain tissue.

Environmental Conditions Affecting Survival

Naegleria fowleri is normally found in the natural environment and is well adapted to surviving in various habitats, particularly warm-water environments. Although the trophozoite stage is relatively sensitive to environmental changes, the cysts are more environmentally hardy.

Drying: Drying appears to make trophozoites nonviable instantaneously and cysts nonviable in less than 5 minutes.

Temperature: Naegleria fowleri is a heat-loving (thermophilic) ameba able to grow and survive at higher temperatures, such as those found in hot springs and in the human body, even under fever temperatures. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C). Although the amebae may not be able to grow well, Naegleria fowleri can still survive at higher temperatures for short periods of time. The trophozoites and cysts can survive from minutes to hours at 122–149°F (50–65°C), with the cysts being more resistant at these temperatures. Although trophozoites are killed rapidly by refrigeration, cysts can survive for weeks to months at cold temperatures above freezing, although they appear to be sensitive to freezing. As a result, colder temperatures are likely to cause Naegleria fowleri to encyst in lake and river sediment, where the cyst is offered more protection from freezing water temperatures.

Disinfection: Naegleria fowleri trophozoites and the more resistant cysts are sensitive to disinfectants like chlorine and monochloramine. Chlorine is the most common disinfectant used to treat drinking water and swimming pools. The chlorine sensitivity of Naegleria fowleri is moderate and in the same range as the cysts from Giardia intestinalis, another waterborne pathogen. The inactivation data for Naegleria are limited, but recent CT values (concentration of disinfectant [mg/l] X contact time [in minutes]) have been developed. Under laboratory conditions, chlorine at a concentration of 1 ppm (1 mg/L) added to 104.4°F (38°C) clear (non-turbid) well water at a pH of 8.01 will reduce the number of viable and more resistant Naegleria fowleri cysts by 99.99% (4 logs) in 56 minutes (CT of 56). Cloudy (turbid) water requires longer disinfection times or higher concentrations of disinfectant.

Salinity: Naegleria fowleri does not survive in sea water and has not been detected in sea water.

Environmental Testing

In general, CDC does not recommend testing rivers and lakes for the presence of Naegleria fowleri in areas where the ameba is known to naturally occur. There is no established relationship between detection or concentration of Naegleria fowleri and risk of infection. Environmental testing may be warranted for investigations in which Naegleria fowleri detection may be useful for establishing geographical distribution or occurrence in new environments, including disinfected water bodies or household water systems. Public health practitioners can contact CDC’s Emergency Operations Center at 770-488-7100 to discuss possible environmental testing with Naegleria fowleri experts if a case of PAM is confirmed.

Naegleria fowleri is a free-living ameba that causes primary amebic meningoencephalitis (PAM), a disease of the central nervous system. PAM is a rare disease* that is almost always fatal. In the United States**, there have been 154 PAM infections from 1962 through 2021 with only four survivors. These infections have primarily occurred in 15 southern-tier states, with almost half of all infections occurring in Texas and Florida. PAM also disproportionately affects males and children. The reason for this distribution pattern is unclear but may reflect the types of water activities (such as diving or watersports) that might be more common among young boys.

Where Naegleria fowleri is Found

Naegleria fowleri is a heat-loving (thermophilic) ameba found around the world. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C) and can survive for short periods at higher temperatures. Naegleria fowleri is naturally found in warm freshwater environments such as lakes and rivers, naturally hot (geothermal) water such as hot springs, warm water discharge from industrial or power plants, geothermal well water, poorly maintained or minimally chlorinated swimming pools, water heaters, and soil, where it lives by feeding on bacteria and other microbes in the environment. Sampling of lakes in the southern tier of the U.S. indicates that Naegleria fowleri is commonly present in many southern tier lakes in the U.S. during the summer but infections have also recently occurred in northern states. Naegleria is not found in salt water, like the ocean.

Where PAM Infections Have Occurred

PAM infections have been reported from around the world. Infections have primarily occurred in southern-tier states in the U.S., but infections were documented in Minnesota in 2010 and 2012 and other northern states since that time. Almost half of all reported infections have occurred in Florida and Texas. In the United States and the rest of the world, PAM is primarily spread via swimming in warm freshwater lakes and rivers (about 3 out of 4 U.S. infections from 1962-2021). Other recreational water types like hot springs and canals have also been linked to PAM infections.

Six infections in the U.S. have been associated with using water from drinking water systems to swim or use a slip-n-slide, immerse the head in a bathtub,  mix solutions for nasal irrigation using a neti pot, or perform ritual nasal rinsing or ablution. PAM infections also occurred in the 1970s and 1980s in Australia that were linked to showering, swimming, or having other nasal exposure to contaminated drinking water. The infections were linked to piping drinking water overland, sometimes for hundreds of kilometers, that resulted in the water being heated and having low to zero disinfectant levels that resulted in the water and pipes becoming colonized by Naegleria fowleri. Several water systems in the states of Western Australia and South Australia continue to monitor regularly for Naegleria fowleri colonization in drinking water distribution systems. Infections due to contaminated water being used for religious practices have also been reported.

Number of PAM Infections

PAM is a rare* disease. From 1962-2021, 154 infections in the U.S. have been reported to CDC. Other infections have been diagnosed in stored autopsy samples dating back to 1937. The annual number of U.S. infections ranges from 0 to 8, with higher numbers appearing to occur in heat wave years when air and water temperatures are higher. It does not appear that the number of infections has increased since CDC established its Free-living Ameba (FLA) Laboratory and PAM registry in 1978.

How PAM is Spread or Transmitted

You cannot get infected from drinking water contaminated with Naegleria. You can only be infected when contaminated water goes up into your nose.

People become infected when water containing Naegleria fowleri enters the nose, usually while swimming. People do not get infected by drinking contaminated water. The ameba migrates to the brain along the olfactory nerve, through a bony plate in the skull called the cribriform plate, where it reaches the brain and begins to destroy the brain tissue. Naegleria fowleri has not been shown to spread via water vapor or aerosol droplets (such as shower mist or vapor generated from a humidifier). The ameba has never been shown to have spread from one person to another.

Transplantation of organs from donors infected by Naegleria fowleri has been recorded, although none of the organ recipients became infected. However, the occurrence of Naegleria fowleri outside the brain has been observed; Naegleria fowleri has been documented in tissue sections of lung, kidney, heart, spleen, and thyroid from two deceased PAM cases. As a result, although the risk of transmission of Naegleria fowleri by donor organs is still unknown, it is likely possible. Therefore, the risks of transplantation with an organ possibly harboring Naegleria fowleri should be carefully weighed for each individual organ recipient against the potentially greater risk of delaying transplantation while waiting for another suitable organ. This warrants continued study of the benefits and risks of transplanting organs or tissues from people infected by Naegleria fowleri.

*Rare Disease
There is no universal definition of a “rare disease” but the U.S. Rare Disease Act of 2002 defined a rare disease as affecting less than 200,000 people in the U.S. and this definition has been adopted by the National Institutes of Health, Genetic and Rare Diseases Information Centers.

**Including U.S. states, territories, and commonwealths.

You cannot get infected from drinking water contaminated with Naegleria. You can only be infected when contaminated water goes up into your nose.

Primary amebic meningoencephalitis (PAM) is a disease of the central nervous system. PAM is caused by Naegleria fowleri, a free-living ameba. It is a rare disease* that is almost always fatal ; only four people in the U.S. out of 154 have survived infection from 1962 to 2021. Signs and symptoms of Naegleria fowleri infection are clinically similar to bacterial meningitis, which lowers the chances of initially diagnosing PAM. Humans become infected when water containing Naegleria fowleri enters the nose and the ameba migrates to the brain along the olfactory nerve. People do not become infected from drinking contaminated water. Symptoms start 1-9 days (median 5 days) after swimming or other nasal exposure to Naegleria-containing water. People die 1-18 days (median 5 days) after symptoms begin. PAM is difficult to detect because the disease progresses rapidly so that diagnosis is usually made after death. Signs and symptoms of the infection include:

Stage 1

• Severe frontal headache
• Fever
• Nausea
• Vomiting

Stage 2

• Stiff neck
• Seizures
• Altered mental status
• Hallucinations
• Coma

The disease is generally fatal; among well-documented cases, there are only five known survivors in North America: one from the United States in 1978, one from Mexico in 2003, two from the United States in 2013, and one from the United States in 2016. The first U.S. survivor’s condition gradually improved during a one-month hospitalization. The only reported side effect to treatment was a reduction in leg sensation for two months after discharge, which gradually improved. There was also no detection of Naegleria fowleri 3 days post-treatment. It has been suggested that the first survivor’s strain of Naegleria fowleri may have been less virulent, which contributed to the patient’s recovery. In laboratory experiments, a California survivor’s strain did not cause damage to cells as quickly as other strains, suggesting that it is less virulent than strains recovered from other fatal cases.

The Mexico survivor’s condition did not begin to improve until 40 hours after hospital admission. On day 22 of admission, there was no abnormality shown in the brain scan and the patient was discharged the next day. The patient was followed up for the next 12 months without any recurrence of disease.

After 35 years without a Naegleria survivor in the United States, during the summer of 2013, two children with Naegleria fowleri infection survived. The first, a 12-year-old girl, was diagnosed with PAM approximately 30 hours after becoming ill and was started on the recommended treatment within 36 hours. She also received the investigational drug miltefosine, and her brain swelling was aggressively managed with treatments that included therapeutic hypothermia (cooling the body below normal body temperature). This patient made a full neurologic recovery and returned to school. Her recovery has been attributed to early diagnosis and treatment and novel therapeutics including miltefosine and hypothermia.

The second, an 8-year-old child, is also considered a PAM survivor, although he has suffered what is likely permanent brain damage. He was also treated with miltefosine but was diagnosed and treated several days after his symptoms began. Therapeutic hypothermia was not used in this case.

In the summer of 2016, a 16-year-old boy was reported as the fourth U.S. PAM survivor. This patient was diagnosed within hours of presentation to the hospital and was treated with the same protocol used for the 12-year-old 2013 survivor. This patient also made a full neurologic recovery and returned to school.

Overall, the outlook for people who get this disease is poor, although early diagnosis and new treatments might increase the chances for survival.

Primary amebic meningoencephalitis (PAM) is a serious brain infection caused by Naegleria fowleri. The disease is diagnosed using laboratory tests, but these tests are available in only a few laboratories in the United States. Because the infection is so rare and hard to detect at first, diagnosis sometimes happens after the patient’s death.

PAM can be diagnosed in the laboratory by detecting Naegleria fowleri organisms, nucleic acid, or antigens in a patient’s cerebrospinal fluid (CSF) or brain tissue.

Primary Amebic Meningoencephalitis (PAM) is treated with a combination of drugs, often including amphotericin B, azithromycin, fluconazole, rifampin, miltefosine, and dexamethasone. These drugs are used because they are thought to have activity against Naegleria fowleri and have been used to treat patients who survived. Miltefosine is the newest of these drugs and has shown ameba-killing activity against free-living amebae, including Naegleria fowleri, in the laboratory. Miltefosine has also been used to successfully treat patients infected with Balamuthia and disseminated Acanthamoeba infection.

Although most cases of primary amebic meningoencephalitis (PAM) caused by Naegleria fowleri infection in the United States have been fatal (150/154 in the U.S.), there have been five documented survivors in North America: one in the U.S. in 1978, one in Mexico in 2003, two additional survivors from the U.S. in 2013 , and one from the U.S. in 2016. It has been suggested that the original U.S. survivor’s strain of Naegleria fowleri was less virulent, which contributed to the patient’s recovery. In laboratory experiments, the original U.S. survivor’s strain did not cause damage to cells as rapidly as other strains, suggesting that it is less virulent than strains recovered from other fatal infections.

After 35 years without a Naegleria survivor in the United States, during the summer of 2013, two children with Naegleria fowleri infection survived. The first, a 12-year-old girl, was diagnosed with PAM approximately 30 hours after becoming ill and was started on the recommended treatment of amphotericin B, fluconazole, rifampin, azithromycin, and dexamethasone within 36 hours. She also received the investigational drug miltefosine and her brain swelling was aggressively managed with treatments that included cooling the body below normal body temperature (therapeutic hypothermia). This patient made a full neurologic recovery and returned to school. Her recovery has been attributed to early diagnosis and treatment and novel therapeutics including miltefosine and hypothermia.

A second child, an 8-year-old male, is also considered a PAM survivor, although he has suffered what is likely to be permanent brain damage. He was also treated with amphotericin B, fluconazole, rifampin, azithromycin, miltefosine, and dexamethasone but was diagnosed and treated several days after his symptoms began. Cooling of the body below normal body temperature was not used.

In the summer of 2016, a 16-year-old boy was reported as the 4th U.S. PAM survivor. This patient was diagnosed within hours of presentation to the hospital and was treated with the same protocol used for the 12-year-old 2013 survivor. This patient also made a full neurologic recovery and returned to school.

Naegleria fowleri infects people when water containing the ameba enters the body through the nose. Infection is rare and typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. Very rarely, infections have been reported when people submerge their heads, cleanse their noses during religious practices, or irrigate their sinuses (nose) using contaminated tap or faucet water. Naegleria fowleri can grow in pipes, hot water heaters, and water systems, including treated public drinking water systems. You cannot get infected from drinking water contaminated with Naegleria. You can only be infected when contaminated water goes up into your nose.

Risk of Infection

Naegleria fowleri is found naturally in freshwater lakes, rivers, and hot springs in the United States, particularly in southern-tier states, but has recently caused infections as far north as Minnesota. No data exist to accurately estimate the true risk of PAM. Hundreds of millions of visits to swimming venues occur each year in the U.S. that result in 0-8 infections per year. It is unknown why certain persons become infected with the amebae while millions of others exposed to warm recreational fresh waters do not, including those who were swimming with people who became infected.

Attempts have been made to determine what concentration of Naegleria fowleri in the environment poses an unacceptable risk. However, no method currently exists that accurately and reproducibly measures the numbers of amebae in the water. This makes it unclear how a standard might be set to protect human health and how public health officials would measure and enforce such a standard. However, the risk of Naegleria fowleri infection is very low. There have been 31 reported infections in the U.S. in the ten years from 2012 to 2021, despite hundreds of millions of recreational water exposures each year. By comparison, in the ten years from 2010-2019, there were an estimated 3,957 unintentional drowning deaths each year in the US.

Naegleriafowleri, also known as the “brain-eating ameba,” occurs naturally in freshwater bodies, such as lakes, rivers, and hot springs. Infections with Naegleria fowleri are rare, and they occur mainly during the warmer months of July, August, and September.

If water containing the ameba goes up a person’s nose, the ameba can enter the brain and cause a rare and devastating infection called primary amebic meningoencephalitis (PAM), which is almost always fatal.

Naegleriafowleri thrives and multiplies in warm water

In the United States, infections have most often occurred after people went swimming or diving in warm fresh water, such as lakes and rivers. Sometimes infections have happened after people put their head under water in hot springs.

Infections usually occur when temperatures are hot, which results in higher water temperatures and lower water levels.

Because Naegleriafowleri is very common in the environment, public health officials can’t control levels of the amebae that naturally occur in fresh water. The location and number of amebae in the water can vary over time within the same lake or river.

In very rare instances, Naegleria fowleri has been found in inadequately chlorinated water, including in pools, splash pads, and a surf park. Naegleria fowleri is not found in salt water, such as the ocean.

Take precautions while enjoying water activities in fresh water

Most Naegleria fowleri infections occur in young boys, although the reasons for this aren’t clear.

It’s possible that young boys are more likely to participate in such activities as diving into the water and playing in the sediment at the bottom of lakes and rivers.

People should always assume there is a risk for infection whenever entering warm fresh water. The only sure way to prevent an infection is to avoid water-related activities in warm fresh water, especially during summer months.

If you choose to swim, you can reduce your risk of infection by trying to prevent water from going up your nose.

• Avoid jumping or diving into bodies of warm fresh water, especially during the summer.
• Hold your nose shut, use nose clips, or keep your head above water when in bodies of warm fresh water.
• Avoid putting your head under water in hot springs and other untreated geothermal waters.
• Avoid digging in, or stirring up, the sediment in shallow, warm fresh water. The amebae are more likely to live in sediment at the bottom of lakes, ponds, and rivers.

Seek medical attention if you or someone you know develops a headache, fever, or vomiting after swimming in fresh water. Initial symptoms of PAM start about 5 days after infection but could begin anytime from 1 to 12 days.

Most Naegleria fowleri infections are associated with swimming in warm freshwater lakes and rivers. However, very rarely, Naegleria fowleri has caused deaths associated with tap or faucet water going up the nose. Naegleria fowleri can grow in public and private water tanks and pipes, especially where little or no disinfectant (like chlorine or chloramine) is present. It can also grow in the pipes and water heaters of homes and buildings.

Naegleria fowleri infections have been reported when people put their heads underwater, rinse their sinuses through the nose, and cleanse their noses during religious practices using contaminated tap or faucet water.