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There has been much in the news lately about Naegleria fowleri, a water-borne amoeba that can cause fatal infections. What is it and what is the risk to whom? Stan Deresinski, MD, infectious disease physician at Stanford University, provides some answers in the October 2013 issue of Infectious Disease Alert:
In 2011, 2 men died of amebic meningoencephalitis in Louisiana. Each had, used neti pots to irrigate their sinuses with tap water, which was, as a result, suspected as the source of infection. However, the proof was not forthcoming, although vigorous sinus irrigation with tap water had previously been associated with the development of this infection.(1) In August 2012, a 4- year-old child in Louisiana’s St. Bernard Parish -- who had been playing on a Slip’n Slide whose water flow came from a household faucet -- died of the infection of the same infection.(2) This time, the CDC detected Naegleria fowleri, the cause of amebic meningoencephalitis, in multiple household water samples, including one collected from the outside faucet that had been used, a water heater, and a toilet tank. The organism was also detected in water samples from nearby hydrants and faucets directly connected to water lines.
Naegleria fowleri is found naturally in freshwater lakes, rivers, and hot springs in the U.S., particularly in southern-tier states. (3,4) It is a thermophilic amoeba with an optimal growth temperature of 115°F (46°C). It is global in distribution and 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. It is not found in salt water.
Infection occurs when the organism enters the nares and migrates along the olfactory nerve through the cribriform plate and into the central nervous system. N. fowleri causes a purulent meningitis heralded by the abrupt onset of severe headache followed by vomiting with progression to coma and, most often, death. The diagnosis is made by visualization of the organism in cerebrospinal fluid or tissue samples, PCR, or growth in tissue or axenic culture at elevated temperature
Recreational water users should assume that there is always a low-level of risk whenever they enter warm freshwater lakes, rivers, and hot springs (for example, when swimming, diving, or waterskiing), particularly in the southern U.S. (although infection has occurred as far north as Minnesota) and particularly in warm months. The infection is rare, with only 32 cases reported in the US from 2001-2010. Of these, 30 had been infected by exposure to contaminated recreational water and 2 by water from a geothermal drinking water supply.
Only 1 of the first 128 U.S. patients have survived the infection, although another survivor has been reported in Mexico.
For more on this story see the October 2013 issue of IDA
1. Shakoor S, Beg MA, Mahmood SF, et al. Primary amebic meningoencephalitis caused by Naegleria fowlerii, Karachi, Pakistan. Emerg Infect Dis 2011; 17:258-61.