BACKGROUND: Primary amebic meningoencephalitis (PAM) is a fulminant central nervous system infection caused by the thermophilic free-living ameba, Naegleria fowleri, which thrives in warm freshwater. The Free-Living and Intestinal Ameba Laboratory (FLIA) at CDC is one of the few places in the United States that can confirm a diagnosis of PAM. Although 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 informal surveillance has documented substantial changes in the epidemiology of PAM in the United States over the past five years.
METHODS: We analyzed data from CDC’s free-living ameba surveillance system for laboratory-confirmed PAM cases from 1962–2015, and describe, in detail, cases from 2010–2015 to examine the recent epidemiology of PAM in the United States.
RESULTS: There have been 138 cases of PAM reported in the United States from 1962 through 2015. During 2010–2015, 24 cases of PAM were reported to CDC and confirmed by the FLIA Laboratory (4 in 2010, 5 each in 2011 and 2012, 4 in 2013, 1 in 2014, and 5 in 2015). Cases were reported from 13 states and territories (AZ, AR, CA, FL, IN, KS, LA, MN, OK, SC, TX, VA, and USVI). Sixty-three percent of cases were female and the median age was 11 years (range: 4–56 years). Nineteen (79%) cases had exposure to recreational freshwater from a lake, reservoir, river, stream, or ditch during their incubation period. Five (21%) cases were exposed to piped water via nasal irrigation using a neti pot (2 cases), nasal irrigation for ritual ablution (1), play on a backyard waterslide (1), and swimming in a poorly maintained pool using warm water piped overland (1).
CONCLUSIONS: 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.