Amoebic meningitis (Naegleria fowleri) – warning for water utilities
Water supplies at risk of Naegleria fowleri must ensure adequate primary disinfection (C.t >30 mg/L.min) and maintain a chlorine residual of at least 0.5 mg/L at all times, in all parts of their network to avoid potentially fatal amoebic meningitis.
Any water supply that seasonally exceeds 30°C or continually exceeds 25°C can support the growth of Naegleria.
Regularly monitor water temperature and chlorine residual throughout the entire distribution system.
What is Naegleria fowleri?
Naegleria fowleri is an amoeba (microorganism), commonly found in warm freshwater and soil. It can cause a very rare but often fatal infection (amoebic meningitis or meningoencephalitis) if contaminated water goes up into the nose.
What water supplies could be at risk?
Any unchlorinated (or poorly chlorinated) water supply that seasonally exceeds 30°C or continually exceeds 25°C can support the growth of Naegleria. This includes reticulated raw water, reticulated drinking water, lakes, rivers, dams, bores, tanks, reservoirs, pipelines, natural hot waters/springs, and spa and swimming pools that are poorly maintained, under-chlorinated or unchlorinated. Low water usage, stagnation of water in pipes, biofilm and sediment build up, inadequate chlorination and warm air temperatures contribute to favourable conditions for growth of the organism. Naegleria cannot survive in water that is clean, cool and adequately chlorinated.
How is it contracted?
Contaminated water can enter the body through the nose, allowing the organism to then reach the brain. This may occur when people swim, dive or fall into warm water containing Naegleria, when children play under sprinklers or with hoses using this water, or when infected water is inhaled to cleanse the nasal passages. Children and young adults appear to be more susceptible to infections than adults. Infections usually occur when it is hot for prolonged periods of time, which result in higher water temperatures. You cannot get infected by swallowing water containing Naegleria.
Although Naegleria fowleri is commonly found in the environment, infection is rare. The organism was first identified in South Australia during the 1960s. A number of cases of infection occurred in towns there served by unchlorinated water delivered through long above-ground pipelines. Cases of amoebic meningitis have been recorded in South Australia, Western Australia, Queensland and New South Wales, and in many countries throughout the world. Recent cases in Australia have been associated with exposure to untreated private water supplies (bore water and a farm dam). Most Australian victims have been children.
How is the risk managed?
- Water utilities should regularly monitor water temperature and chlorine residual throughout the entire distribution system. NSW Health recommends that water temperature is recorded as a field measurement with all microbiology samples.
- As Naegleria fowleri occurs and grows naturally in warm waters, it should be assumed that any warm freshwater could contain Naegleria. A risk management approach should be applied at all times.
- For drinking water supplies, treatment such as chlorination can control Naegleria. Naegleria is not associated with faecal contamination and can occur in the absence of E. coli.
- Adequate primary disinfection must be applied to achieve a C.t of greater than 30 mg/L.min.
- A free chlorine (or chloramine) residual should be maintained at or above 0.5 mg/L throughout the entire distribution system. Naegleria are most likely to enter a water supply system at the source or at breaks in the sealed system such as open reservoirs and tanks. Under favourable conditions, such as warm unchlorinated water or fluctuating chlorine residual, Naegleria can proliferate in pipework and tanks and enter into a cyst state that is more resistant to disinfection. Cysts can survive in tank sediments and pipe biofilm.
- If adequate disinfection cannot be maintained throughout the distribution system, a monitoring program for thermophilic Naegleria species in raw and treated water should be developed in consultation with NSW Health.
- Households should also be warned of the potential risk, if adequate disinfection cannot be maintained throughout the distribution system (see NSW Health Fact Sheet - Amoebic meningitis (Naegleria fowleri) – warning for households).
- Proper design, management and cleaning of assets (e.g. pipes and storage tanks) is required to minimise sediment (which may harbour Naegleria cysts) and reduce water stagnation (which may lead to loss of disinfectant residual).
Testing for Naegleria fowleri
- Testing water for Naegleria fowleri is very specialised and expensive. Additionally, the absence of Naegleria fowleri does not necessarily indicate or guarantee that the water is free of the organism at all times. A risk management approach should be applied at all times.
- Periodic testing for Naegleria fowleri can be carried out in at risk systems, but regular monitoring is not warranted unless Naegleria fowleri is detected.
- Testing for thermophilic Naegleria can help monitor risk, especially where an adequate chlorine residual cannot be maintained throughout the distribution. Thermophilic Naegleria are a ‘proxy’ for Naegleria fowleri, allowing early remedial action. If thermophilic Naegleria are detected, corrective action should be initiated while identification of the Naegleria species is undertaken.
- Incident management protocols should be developed in consultation with NSW Health prior to testing for thermophilic Naegleria. The Australian Drinking Water Guidelines recommend utilities should aim for free chlorine and chloramine residuals of at least 1 mg/L throughout the distribution system when thermophilic Naegleria have been found.
- Actions to increase residual in the water supply system include increasing disinfection (e.g. chlorine dose), tank disinfectant dosing, mains flushing, and localised dosing. For more information see the Australian Drinking Water Guidelines (Example response protocol Box 10.4 page 164 and Fact Sheet page 322).
Recording water temperature
NSW Health requests that water utilities include temperature as a field test when microbiology samples are collected as part of the NSW Health Drinking Water Monitoring Program. This will help to identify drinking water supplies that may be at risk from Naegleria fowleri.
Following tap disinfection and flushing, take a sample and then measure the temperature of the water coming from the tap. Do not use the sterile microbiology container to measure temperature. Please record the temperature in the ‘Comments’ field on the Allocated Microbiology labels (white) (and on the Additional (blue) or Repeat (pink) labels when used for microbiology).
For more information
Contact your local Public Health Unit on 1300 066 055 and refer to: