The Investigation of Amebic Meningoencephalitis from Whitewater Park

The environmental investigation that followed the death of an 18-year-old girl in 2016 from primary amebic meningoencephalitis (PAM) contracted in a whitewater recreation park was detailed in a recent report by an epidemiologist from the Centers for Disease Control and Prevention (CDC).

Jennifer Cope, MD, MPH, a medical epidemiologist in the Waterborne Disease Prevention Branch of the CDC commented to MD Magazine on their discovery of the novel type of water transmission for Naegleria fowleri (N. fowleri).

"We embarked on this investigation when, during the course of asking our standard water exposure questions for when a PAM case is identified, we determined that the most likely water exposure occurred in an artificial whitewater river, which had never been reported before," Cope said.

The organism implicated in the death, N. fowleri, is an ameba that thrives in warm freshwater, causing PAM when it enters the nose and gains access to the brain via the cribriform plate.

The resulting infection progresses rapidly, causing death in 97% of cases reported in the U.S. (143 since 1962) in a median of 5 days. The presentation of PAM is often mistaken for more common types of meningitis, and the diagnosis is often made post-mortem.

Cope, with colleagues at the involved State public health departments, reported that this patient had been treated empirically for bacterial and viral etiologies of meningitis, with ceftriaxone, vancomycin, ampicillin, doxycycline, and acyclovir.

Her course continued to deteriorate, with efforts to reduce diffuse cerebral edema and increasing intracranial pressure including administration of mannitol, hypertonic saline, dexamethasone, hyperventilation, pentobarbital. Vasopressors were also administered to increase mean arterial pressure and generate cerebral perfusion pressure.

The cerebrospinal fluid gram stain had not revealed any organism, and the CDC was contacted two days after the patient was admitted, with the possibility that PAM was causing the rapid deterioration despite conventional treatments.

On their recommendation, based on treatment protocols which had been used in PAM survivors, the patient then received amphotericin B, fluconazole, azithromycin and rifampin. The antiparasitic agent miltefosine (Impavido) was started 8 hours later when it arrived from the CDC, but only 1 dose was administered before the patient succumbed.

Cerebrospinal fluid samples arriving at CDC two days after the death were subjected to real-time polymerase chain reaction (PCR) tests and revealed N. fowleri. The family related that the patient had fallen out of a raft at the US National Whitewater Center (USNWC) in North Carolina the week prior to hospitalization.

Cope and her team found that the USNWC is filled from onsite wells and county municipal water. No river water is introduced into the system and drainage around the side is graded to minimize runoff into the whitewater channels.

The USNWC actively filters the volume of the park over each 24 hour period and passes water through a low-pressure ultraviolet (UV) treatment unit to an upper storage pond before release into the channels. Chlorination is added in the upper pond when testing indicates increasing fecal coliform counts or algai growth is visible. Sediment and algai are vacuumed from the upper pond when the pumps are off.

Cope and colleagues report finding that the chlorine concentrations were not monitored, and that there was residual water in the channels. On the date of inspection, when the pumps were turned off, there was a layer of algae and biofilm in the upper pond and channel surfaces, which is conducive to amebae growth.

They characterized the average water temperature of 30 degrees Celsius as ideal for a thermophilic organism like N. fowleri. They also found that the 200-micron size filter being used was inadequate for removal of microorganisms, and that the turbidity of the water could reduce penetration of UV and chlorination.

Water samples obtained from the whitewater park, at small and large volume water sites, from the filter backwash, and from surface swabs, all tested positive for N.fowleri. The cycle threshold (Ct) value for samples from the top pond sample was comparable to those seen for culture, and did not require concentration to detect amebae.

The remediation plan proposed by the CDC included modifying the filtration system and adding ozonation and an automated chlorine injection system to maintain 0.5 ppm of free chlorine. The CDC also worked with the local Board of Health on regulations applicable to the whitewater park environment, and recommended that park users take such personal actions to reduce the risk of PAM as keeping the head above water, and using nose clips.

"Our study demonstrates the difficulties that will be faced by public health officials as more recreational water venues that do not meet the traditional definition of a swimming pool or water park are built and opened," Cope said.

The manuscript, "Primary Amebic Meningoencephalitis Associated with Rafting on an Artificial Whitewater River: Case Report and Environmental Investigation," was published online in Clinical Infectious Diseases last month.