2014-03-12 08:38:42
The pathogenic free-living amoebas of the species Naegleria fowleri are responsible for primary amoebic meningoencephalitis (MEAP), an uncommon but fatal disease in 95% of cases. Indeed, for 50 years, 310 cases have been recorded worldwide, and only 11 people have survived.
These amoebas live in fresh waters whose temperature exceeds 25°C. This is particularly the case of bathing sites located downstream of discharges from the cooling circuits of thermal power plants, which are subject to reinforced health checks, including research for free amoebae in the water. In accordance with the recommendations of the Higher Council of Public Hygiene of France (CSHPF), swimming is prohibited when the threshold of 100 N. fowleri per liter of water is exceeded.
To date, one case of MEAP has been reported in France in 2008. A 9-year-old boy died of lightning meningitis following swimming and diving in a pool fed by a hot spring in Guadeloupe, where the presence of N. fowleri has been detected. Analyzes have shown the presence of N. fowleri in the victim’s cerebrospinal fluid and confirmed the diagnosis of MEAP.
ANSES’s work
In this context, the Agency was asked by the Ministry for Health to assess the risks associated with the presence of a species of free-living amoebae N. fowleri in bathing waters. A review of the literature was therefore carried out with the aim of:
- determine the factors likely to promote the development of N. fowleri in waters and particularly in bathing waters;
- to analyze the sampling and identification methods of N. fowleri ;
- to propose measures to control the health risk for humans according to the types of bathing.
A rare risk of infection
N. fowlerihas been detected in freshwater mainly in summer and autumn in different regions of the globe and in all types of bathing:
- swimming in open water;
- swimming pools, hot tubs;
- natural bathing sites fed by waters of geothermal origin.
No case of MEAP has, to date, been identified following swimming in France in an artificial pool.
In view of the very low number of recorded cases of MEAP due to N. fowleri in France and around the world (310 cases for 50 years, including only one in France) and very specific methods of exposure (hot water, flooding of the nasal cavity during diving, for example), ANSES believes that infection with this bacterium remains a rare event.
Thus, the risk to public health is low compared to that of other bathing-related infectious diseases.
Recommendations
Given the complexity of finding N. fowleri in the aquatic environment, ANSES recalls the need to optimize detection methods and stresses the importance of harmonizing sampling, identification and quantification methods for this amoeba.
The Agency recommends limiting the exposure of bathers according to the type of bathing. Experts echo CDC recommendations[1] which indicate that, for all bathing activities, the only effective measure for preventing infection with N. fowleri is to avoid being exposed to it and therefore to refrain from bathing in hot or heated water, especially when the air temperature is high and the water level is low.
ANSES also recalls that compliance with the conditions for implementing the disinfection treatments currently authorized in France for the water supplying public swimming pools is sufficient to prevent the risk of water contamination by this species of free-living amoeba.
In its opinion of July 17, 2009 relating to the assessment of the health risks associated with artificial swimming pools, the Agency recommended minimum technical requirements to be complied with for the operation of an artificial swimming pool. Compliance with these recommendations appears sufficient for the management of the health risk associated with N. fowleri.
In addition, the Agency paid particular attention in its expert report to bathing sites supplied by hot water of geothermal origin in natural sites which are not subject to a regulatory framework.
Finally, ANSES is also proposing measures to improve knowledge, in particular of this species of free-living amoeba and of the level of contamination of water at the national level, which will make it possible to continue the assessment of health risks.
[1]Centers for disease control and prevention (USA)
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