Amoeba: Naegleria fowleri Brain Infection Rare but Fatal

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

The death of six people in summer 2007 as a result of infection with the Naegleria fowleri amoeba raised widespread awareness of this rare infection. Naegleria fowleri is an amoeba found worldwide in warm bodies of water, but human infection is extremely rare. Until the six cases in summer 2007, the U.S. Centers for Disease Control and Prevention (CDC) reported only 23 cases of the condition between 1995 and 2004.

All of those who died in 2007 were believed to have contracted the infection from swimming in freshwater lakes, rivers, or springs during the hot summer months. Health Department officials in the affected areas pointed out that hot air temperatures raised water temperatures to levels (above 80 degrees Fahrenheit) in which the amoeba thrives. The victims in summer 2007 were all young males between the ages of 10 and 22. Those who swim in warm freshwater sources, particularly those who participate in water sports and play in a manner in which entry of water into the nose is likely, are at risk for the infection.

The Naegleria fowleri amoeba enters the nose and then migrates to the brain to cause a disease known as primary amebic meningoencephalitis (PAM). Symptoms, typically those of a flu-like illness, begin within two weeks of exposure. The symptoms worsen quickly until coma and brain death ensue. Certain drugs have been shown to be effective against Naegleria fowleri in the laboratory, but it is not known if these same medications will be effective in treating the condition in humans. Most reported infections of humans have been fatal.

Spread of Naegleria infection from person to person does not occur. It is also not possible to contract Naegleria from a swimming pool if the water has been properly chlorinated and the pool is kept clean and maintained.

It is not possible to know exactly which bodies of water may contain the amoeba at a given point in time, since testing requires several days until the results are available. However, the CDC states that "it is likely that a low risk of Naegleria infection will always be associated with swimming in warm freshwater lakes, rivers, and hot springs."

According to the CDC, preventive measures that may reduce the risk of infection include the following:

  • Avoid swimming or jumping into bodies of warm freshwater, hot springs, and thermally polluted water such as water around power plants. Water sports and play that increase the chances of water entering the nose increase the risk.


  • Avoid swimming or jumping into freshwater during periods of high temperature and low water volume.


  • Hold the nose shut or use nose clips when jumping or diving into bodies of warm freshwater to reduce the likelihood of water entering the nose.


  • Avoid digging in or stirring up the sediment while swimming in shallow, warm freshwater areas.


  • Do not swim in areas posted as "no swimming" or in areas warning about an increased risk of Naegleria infection.

Last Editorial Review: 10/18/2007