A New Hazard
to Recreational Swimmers
By Kelly A.
fowleri is perhaps one of the most daunting waterborne pathogens
known in the United States. Although infections are still rare--with a
1 in 100 million chance of contracting the disease--the fatality rate
is nearly 100 percent, with few treatment options available. The parasitic
protozoa is actually a free-living amoeba, commonly present in soils and
surface waters worldwide with cases reported in diverse locations such
as Europe, Australia, New Zealand, Thailand, Africa, India, Korea, Japan,
Peru, Venezuela, Panama and the United States. Warm waters above 80o F
is where the pathogen multiplies, in conditions specific to the increase
of bacterial food sources.
The amoeba infects
by entering the nasal passages of swimmers, traveling up the cells of
the nervous system to the brain, where it effectively destroys brain tissue,
causing severe illness and usually death within about a week.
was first recognized as a human pathogen in 1965, and since then more
than 179 cases have been recorded, with 81 reported in this country alone.
Infections usually occur in healthy, young people. Because death is so
rapid and almost certain, confirmation of the disease is usually established
post-mortum, after an examination of brain tissue or cerebrospinal fluid.
The pathogen has
been isolated from warm, fresh or brackish water including swimming pools,
ponds, lakes, streams, hot springs, thermally polluted waters, dust, soil
and sewage. N. fowleri can enter nasal passages when water is forced
into the nose via diving or jumping but may also become motile into nasal
cavities if the swimmer is submerged underwater. Cases have also occurred
in persons with no recent contact with water, suggesting an airborne route
where dust particles may have been a carrier of the stable cyst form of
Evidence of Naegleria
presence has mounted over the years. The organism has been isolated from
hot water systems of hospitals, where 22 percent of the samples collected
from six hospitals were positive. In addition, thermal discharges from
power plant facilities greatly contribute to the growth of Naegleria
commonly present in the environment. During periods of thermal additions,
concentrations of N. fowleri increase by as much as two orders
of magnitude.1 Concentrations may not return to previous levels for 30-to-60
days following the cessation of warm water discharges.
A year-round survey
of aquatic environments in Tulsa, Okla., showed that N. fowleri
could be isolated from 18 percent of the 2,016 processed water and swab
samples collected. A study of 30 hot spring spas in Kanagawa, Japan, revealed
that Naegleria could be isolated from 46.7 percent of the samples taken.2
Although the species were not the pathogenic N. fowleri, the presence
of other free-living protozoa suggest the ability for the persistence
of harmful species as well. Finally, in Egypt, Naegleria species
were detected in 12 out of 16 swimming pool samples (75 percent), and
six out of 10 surface water and canal samples (60 percent). Animals may
also become infected with the organism, but little is known about the
role of animal transmission to humans either directly or indirectly.
Since 1971, the
Centers for Disease Control (CDC) and U.S. Environmental Protection Agency
(USEPA) have maintained a collaborative surveillance system for collecting
and periodically reporting data relating to occurrences and causes of
waterborne disease outbreak.3 During the period from 1995-96, 37 outbreaks
from 17 states were attributed to recreational water exposure, affecting
approximately 9,129 persons. Of these, 22 were outbreaks of gastroenteritis
(59 percent); nine were of dermatitis (24.3 percent); and six were of
Primary Amoebic Meningitis (PAM), caused by N. fowleri (16.2 percent),
all six of which were fatal.
N. fowleri usually result in PAM, a deadly disease of the brain with
symptoms usually occurring between 3-to-7 days after infection and including:
-- Swelling and
fluid buildup in the brain,
-- Nose bleeds,
-- Swollen lymph
-- Rapid, shallow
-- Light sensitivity,
-- Severe headache
-- Loss of appetite,
smell and taste, vomiting,
-- Sore throat,
stiff neck and back, cramping, weakness,
-- Confusion, seizures,
If detected early
enough, treatment with antibiotics and anti-fungal medications may prevent
the spread of the disease; however, many of the symptoms listed are the
result of damage that has already occurred in the brain. At least four
persons have been successfully treated following infection.
According to the
CDC, there is an average of 1-to-3 infections in the United States each
year. In 1995, the six fatal cases of PAM attributed to N. fowleri
were all acquired in the summer months (July and August) involving children
ranging in ages from 4-to-11 years. Infection was from a shallow lake,
pond, canal or river. Five of the six cases occurred in Texas and one
have low autopsy rates and thus some researchers believe that the incidence
of N. fowleri and other pathogenic amoeba may be underdiagnosed worldwide.
In one U.S. instance, an 11-year-old boy died of what was diagnosed as
bacterial meningitis. Following donations of several of his organs to
recipient patients, it was later discovered the actual cause of death
was PAM caused by N. fowleri.
N. fowleri is ubiquitous
worldwide and commonly present in surface waters and soils. Free living
amoebae are the main predators of bacterial populations in the environment
and play a major role in the ecological balance of many environmental
systems. Humans are frequently exposed to the amoebic organism but few
infections occur. In most cases it seems a specific set of criteria must
be present before infections ensue. Primarily, the organism must not only
be present but must grow to high numbers-as evidenced by outbreaks in
warm, polluted or stagnant water. In addition, the organism must be introduced
to the nasal passages.
should be aware of disease symptoms following swimming in warm waters.
Swimming in stagnant water is particularly risky, since concentrations
of the pathogen increase in this environment by feeding off resident bacteria.
Recommendations have been issued from tourism agencies instructing swimmers
to avoid submerging themselves completely underwater at hot spring recreational
sites, as N. fowleri should be assumed present.
The use of nose
plugs or holding the nose when jumping into potentially contaminated water
sources is also advised. Warnings from areas where infections have been
documented in the past should be considered. Swimming pools should have
a chlorine residual of at least 1-to-2 parts per million (ppm). After
swimming, remove water from nose by blowing through the nasal passages,
to reduce the chance of Naegleria infections.
As an industry,
there isn't much that can be done to completely eliminate exposures to
N. fowleri. Education of potential exposures and the recommendation of
precautionary measures are primary contributions the water treatment industry
can make to the public regarding this highly fatal pathogen. In addition,
it's imperative to educate others on the importance of exercising control,
where possible, by maintaining proper disinfectant residuals in public
and private pools and spas.
1. Tyndall, R.L.,
K.S. Ironside, P.L. Metler, E.L. Tan, T.C. Hazen, and C.B. Fliermans,
"Effect of thermal additions on the density and distribution of thermophilic
amoebae and pathogenic Naegleria fowleri in a newly created cooling
lake," Applied Environmental Microbiology, 1989. 55(3): p. 722-32.
2. Kuroki, T.,
K. Yagita, E. Yabuuchi, K. Agata, T. Ishima, Y. Katsube, and T. Endo,
"Isolation of Legionella and free-living amoebae at hot spring
spas in Kanagawa, Japan," Kansenshogaku Zasshi, 1998. 72(10): p.
3. Levy, D.A.,
M.S. Bens, G.F. Craun, R.L. Calderon, and B.L. Herwaldt, "Surveillance
for waterborne-disease outbreaks--United States, 1995-1996," Mortality
Weekly Report, CDC Surveillance Summary, 1998. 47(5): p. 1-34.
for control of Amoebic Meningoencephalitis
typical viral or bacterial meningitis or aseptic meningitis involves
only the meningeal cells (thin layers of tissue covering the brain
and spinal cord) and the ependymal cells (cells that make up the
lining membrane of the ventricles of the brain and the central
canal of the spinal cord) and recovery is almost always complete.
meningoencephalitis involves more extensive damage to the brain,
involving the brain parenchyma (living cells of the soft tissue,
i.e., the brain itself) and typically causes death or irreversible
brain damage. Other notes include:
disease of brain, entering via the nasal mucosa and olfactory
nerve and causing a syndrome with symptoms that include sore throat,
severe headache, neck stiffness and death within 10 days, but
usually on the fifth or sixth day.
amoebae are free-living in water, soil and vegetation.
three to seven days
is no person-to-person transmission. No isolation, concurrent
disinfection or quarantine is necessary.
B, miconazole and rifampicin. Recovery from infection is rare.
of contacts and source of infection should take place.
Educate public on the risk of swimming in lakes and ponds where
water is stagnant or where the infection has been acquired
Maintain a residual chlorine of 1-to-2 ppm in swimming pools
Chlorinate public water supplies that are naturally warm.
Department of Human Services, Public Health Division, Government
of Victoria, Australia.