Naegleria fowleri in bathing water: serious but rare infections
Free-living pathogenic amoebae of the species Naegleria fowleri (N. fowleri) are responsible for primary amoebic meningo-encephalitis. A small number of cases of the disease, a severe infection with a 95% fatality rate, have been reported worldwide. In 2008, a 9-year-old boy died following an attack of acute meningitis after bathing and diving in a pool supplied by a hot water spring in Guadeloupe in which N. fowleri was found. Microbiological tests on a sample of cerebrospinal fluid from the child detected the presence of N. fowleri. In this context, ANSES was asked by the Ministry of Health to assess the health risks of the presence of N. fowleri amoebae in bathing water. The Agency published today the opinion and expert assessment report concerning this request, indicating that the health risk of the presence of N. fowleri amoebae in bathing water is low since cases of infection are rare, and issued recommendations in order to limit possible risks of exposure.
Free-living pathogenic amoebae of the species Naegleria fowleri are responsible for primary amoebic meningo-encephalitis (PAM), a rare disease with a fatality rate of 95%. In fact, of the 310 cases of the disease that have been reported worldwide In the last 50 years, only 11 victims survived.
Naegleria fowleriamoebae live in fresh water in temperatures above 25°C. These conditions prevail, for example, in bathing sites located downstream from water discharge points for the cooling circuits of thermal power plants. These sites are subject to reinforced health and safety monitoring, including tests for free-living amoebae in the water. In compliance with the recommendations of the French High Council for Public Hygiene (CSHPF), bathing and swimming activities are forbidden when the number of N. fowleri amoebae per litre of water exceeds 100.
To date, the only case of PAM declared in France occurred in 2008. A 9-year-old boy died following an attack of acute meningitis after bathing and diving in a pool supplied by a hot water spring in Guadeloupe in which N. fowleri was found. Tests detected N. fowleri in the cerebrospinal fluid of the victim and confirmed the PAM diagnosis.
In this context, ANSES was asked by the Ministry of Health to assess the health risks of the presence of free-living N. fowleri amoebae in bathing water. A review of the literature was therefore conducted in order to:
- determine the factors likely to promote the development of N. fowleri in water, and in bathing water in particular;
- analyse the methods of sampling and identification of N. fowleri;
- propose measures for controlling the health risk for humans of the different types of bathing and swimming activities.
A rare risk of infection
N. fowleri has been detected in fresh water mainly in the summer and autumn in various regions of the world and in all types of bathing and swimming water, including:
- improved open-water bathing sites;
- pools, whirlpool baths;
- natural bathing sites supplied with geothermal water.
No cases of PAM have to date been reported as a result of bathing or swimming in France in artificial bathing sites.
Due to the very low number of reported cases of MAP caused by N. fowleri in France and worldwide (310 case in the last 50 years, and just one in France) and to the highly specific conditions of exposure (warm water, flooding of the nasal cavity through diving, for example), ANSES considers that infection with this bacteria is a rare event.
Therefore, the risk to public health is low compared to that of other infectious diseases related to bathing and swimming activities.Recommendations
Due to the complexity of detecting N. fowleri in aquatic environments, ANSES emphasises the need to optimise detection methods and highlights the importance of harmonising methods for the sampling, identification and quantification of the amoeba.
The Agency recommends limiting bather exposure depending on the type of bathing and swimming activity. The experts wish to emphasise the recommendations of the CDC which indicate that, for all bathing and swimming activities, the only effective method for preventing a N. fowleri infection is to avoid exposure, which means avoiding activities in warm or heated water, especially when the air temperature is high and the water level low.
ANSES also emphasises that compliance with the conditions for implementing disinfection treatments currently authorised in France for water supplying public pools is satisfactory for preventing the risk of water contamination by this species of free-living amoeba.
In its opinion dated 17 July 2009 on assessment of the health risks of artificial bathing sites, the Agency recommends the minimum technical requirements which must be complied with when operating an artificial bathing site. Compliance with these recommendations appears to be sufficient for managing the N. fowleri health risk.
In its expert appraisal report the Agency also closely examined unregulated natural bathing sites supplied with warm geothermal water.
In addition, ANSES also has proposed measures for improving knowledge of this species of free-living amoeba and of the contamination levels in water throughout France, in order to pursue health risk assessment in this area.
 Centers for disease control and prevention (USA)