How to prevent the spread of Legionella

What is Legionella?

Legionnaires’ disease or Legionellosis is a severe infection caused by Legionella species, primarily L. pneumophila.

The disease typically presents as pneumonia and symptoms may include a high fever, chills, cough, muscle aches, headaches, and diarrhoea.

The major source for legionella is water distribution systems of large buildings, including hotels and hospitals and the cooling towers of various industries. Recent evidence suggests that "Aspiration" (choking such that secretions in the mouth get past the choking reflexes and enter the lung) is the most common way that bacteria enter into the lungs to cause pneumonia.

Legionella is widespread in nature and found in low quantities in most surface water. It reproduces most in stagnant warm water (± 40°C). This makes it relatively easy for homes and businesses to inadvertently cause fatal infections and outbreaks in workers and the wider public.

Heat-and-flush

Raising the hot water tank temperature to 60-700C; thermal eradication provides only temporary results. There are various drawback to the heat and flush method:

very labour intensive
presents scalding risks
associated high energy costs
corrosion problems
difficult to achieve complete effectiveness and at best provides only short term (weeks to months) effectiveness.

Chlorination

Chlorination (also know at shock chlorination or super-chlorination) is performed by mixing a large amount of sodium hypochlorite, which can be in the form of a powder or a liquid such as chlorine bleach, into the water.

Shock chlorination at 20 to 500 ppm provides only temporary results and is corrosive to pipes and produces potentially carcinogenic DBP’s. Continuous chlorination at 1-2 ppm is not effective. Chlorine is significantly less effective in hot water systems which are the main foci of Legionella proliferation.

This method provides an effective point of source disinfection only, but no residual disinfection. This proves non-effective for systems already contaminated.

There are drawbacks associated with chlorination:
High energy costs
requires very clean water with low turbidity and suspended solids

Turbidity: Similar to smoke in the air, the 'mass' of smoke is made up of tiny particles that are invisible to the naked eye. Turbidity in water is caused by individual, invisible particles that cause a cloudy appearance

UV Radiation and Ozonation

This method must be generated onsite. Commercially available treatment plant costs for small scale systems (such as hospitals and hotels) are high.

This method, while effective involves possible health risks and has been disallowed in some countries.

ESOL use in cooling towers

In a paper published in the Journal of Hospital Infection (Prince, 2002); a comprehensive sampling protocol was employed to evaluate the efficacy of ESOL (electro-chemically activated water), against legionellae and heterotrophic bacteria in two industrial cooling tower systems.

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Both of the towers in the study remained free from evidence of Legionella spp. contamination throughout a five-month evaluation period despite the previously demonstrated presence of legionellae.

Legionella was present in one of the test towers, and in two other towers on the same site, at levels well in excess of UK Health and Safety Commission (HSC) Approved Code of Practice and Guidance (ACOP) upper action limits.