Distribution systems as reservoirs of Naegleria fowleri and other amoebae

Naegleria fowleri is the etiological agent of primary amoebic meningoencephalitis (PAM), a rapidly fatal disease. Although PAM generally occurs after recreational exposure to contaminated water, two fatal cases of PAM were linked to a drinking water supply in Arizona. This study tested the ability of distribution system biofilms to be reservoirs for N. fowleri and other amoebae. When introduced to laboratory pipe loops, N. fowleri attached to biofilms and survived for five months. In two full-scale distribution systems, amoebic activity was detected in 67% of biofilm samples tested, irrespective of chlorination. Amoebic activity occurred mostly in locations associated with stagnant water and high bacterial counts. Legionella were also found in 65% of biofilm samples. Although N. fowleri were never detected in field samples, the observed risk factors-high bacterial counts, amoebic activity, and the presence of Legionella in biofilms-suggest that N. fowleri could thrive in both systems if introduced.