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Changing Epidemiology of Primary Amebic Meningoencephalitis in the United States: What Have We Learned in the Last Five Years?

Posted By Jennifer Cope, Friday, September 30, 2016
Updated: Friday, September 30, 2016

Naegleria fowleri (commonly referred to as the "brain-eating ameba"), is a free-living microscopic ameba. It can cause a rare and devastating infection of the brain called primary amebic meningoencephalitis (PAM) with a mortality rate >97%. The ameba is commonly found in warm freshwater (e.g. lakes, rivers, and hot springs). Naegleria fowleri infects people when water containing the ameba enters the body through the nose. Once the ameba enters the nose, it travels to the brain where it causes PAM. Infection typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. In some instances, Naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or heated and contaminated tap water) enters the nose.

The Free-Living and Intestinal Ameba Laboratory (FLIA) at the Centers for Disease Control and Prevention (CDC) is one of the few places in the United States that can confirm a diagnosis of PAM. Although PAM is not a nationally notifiable condition, CDC collects data on a standardized case report form for all cases confirmed at CDC. Historically, case reports tended to come from southern-tier states in persons exposed to recreational freshwater; in recent years, new geographic areas and modes of transmission have been documented. CDC’s surveillance has documented substantial changes in the epidemiology of PAM in the United States over the past five years (Figure 1).

The summer of 2016 has continued the trend of identifying new types and geographic areas of water exposures associated with PAM cases. For the first time, a patient was diagnosed with PAM after falling out of a whitewater raft on a closed-loop, recirculated artificial whitewater river in North Carolina. An environmental investigation of the whitewater facility identified Naegleria fowleri in all of the samples collected from the artificial whitewater river. Additionally, the first case of PAM associated with water exposure in the state of Maryland was reported in August. This summer also saw the 4th U.S. survivor of PAM. The Florida teenager’s survival was achieved through prompt diagnosis, early anti-amebic treatment, and close monitoring of intracranial pressure.

The epidemiology of PAM in the United States is evolving. Beginning in 2010, the first PAM case was reported from Minnesota, 600 miles farther north than a case had ever previously been reported. While CDC continues to see cases with recreational freshwater exposures, we have now documented cases associated with the use of piped water, bringing to light the threat posed by Naegleria colonizing building plumbing and water distribution systems. Standardized surveillance and reporting of amebic encephalitis, including PAM, is crucial to understanding the changing epidemiology. When state and local health departments are notified of a possible PAM case, they are encouraged to contact CDC 24/7 (via the Emergency Operations Center at 770-488-7100), where a CDC subject matter expert can provide treatment recommendations for clinicians, specimen submission instructions for testing of specimens at CDC, and guidance for conducting an epidemiologic investigation of water exposures.


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