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A Legionnaire’s disease case or outbreak is usually seen by risk assessors
as a result of a chain of situations: 1. Contamination: the
Legionella
bacteria
enters a given water system; 2. Amplification: specific conditions of water
quality and system operation promote
Legionella
growth within the system;
3. Dissemination: particular system features create conditions for
Legionella
dissemination to the environment (such as cooling towers, showers,
fountains, sprinklers); 4. Infection: individual or community contact
with water droplets contaminated by
Legionella
causing legionellosis.
Technically, based on all the characteristics of
Legionella
, assumed
in any assessment that any system contamination is inevitable. There
is no reasonable or efficient method capable enough of preventing
Legionella
to contaminate a system and any source of water is likely
to be contaminated. As a risk assessor, I have witnessed water systems
contaminated with
Legionella
from all different sources: artesian wells,
surface water, rainwater, industrial reuse, public water providers. Thus,
the risks to be brought up for consideration and characterized in the
systems should start from an overview of system conditions, the water
source and water quality in the system to identify the risks of
Legionella
amplifying, spreading outside the system and having contact with people.
When all reasonable risks are identified, mapped and characterized, it
is necessary to develop a comprehensive management plan for mitigation
of these risks. This plan must be prepared by a competent risk assessor
and implemented by the person in charge for the water system assessed.
The last stage is a form of an audit of the process in place: a validation
process is performed to ascertain whether the risk is effectively managed,
and a verification is made to assess if the plan is properly implemented.
