Environmental Investigation and Response to Second Naegleria Fowleri Case Associated with a Community Water Park in Arkansas – July 2013

BACKGROUND:   Primary Amebic Meningoencephalitis (PAM) is a rare but highly fatal disease caused by Naegleria fowleri, a free-living ameba found in soil and in warm natural waters.  In July 2013, a young girl was diagnosed with PAM.  She reported swimming at a local water park, which was also associated with another Naegleria case in 2010.  During the incubation period for PAM, she also swam at another public beach and a hotel pool.  The Arkansas Department of Health (ADH) investigated to determine the source of her Naegleria infection, and to ascertain whether others were at elevated risk of Naegleria.

METHODS:   Each site underwent environmental sampling.  Water temperatures and chlorine levels were measured.  Sampling sites were mapped and average depths of each location were recorded.  Water and sediment samples were submitted to the Centers for Disease Control for identification of ameba by polymerase chain reaction (PCR) and culture methodologies.

RESULTS:   Naegleria was not found in samples from the swim beach or the hotel pool by PCR or culture.  All four sediment samples from the park were positive for Naegleria by both culture and direct PCR.  The water column sample from the park was negative by culture but positive for Naegleria by PCR.   Both water and sediment samples collected from the park in 2010 were also positive for Naegleria by PCR.  Free chlorine levels at the park averaged 0.49 mg/l on the day of sampling – well below the target level of 1 mg/l, with a water temperature of 29^o C. (85^o F).  The swimming area within the park measured ~100 by ~150 meters with a maximum depth of ~1.5 meters.  It had a sandy bottom and its water came from both a natural spring and runoff.  Several slides and water features on site facilitated attendees colliding with the water forcefully.

CONCLUSIONS:   Although Naegleria readily may be found in all warm natural waters, and negative tests performed at one time point do not prove that Naegleria were absent, ADH determined that the most likely source of Naegleria was the water park.  ADH further concluded that high water temperatures due to shallow water depth, the sediment bottom which is infeasible to adequately chlorinate, and water features fostering forceful water impact and entry into the nares created an environment highly conducive to Naegleria transmission.  As a result, ADH requested that the water park cease operations until a solid bottom is installed and adequate chlorination is achieved.