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Legionella bacteria occur naturally in lakes, rivers,
creeks and soil. People usually contract Legionnaires’ disease, a
potentially fatal form of pneumonia, by breathing in very fine
droplets of water called aerosols that have Legionella bacteria
present within them.
Outbreaks of Legionnaires’ disease have been associated with
the following sources:
- Cooling Towers
- Warm water systems
- Spas
- Potting mix
Legionella species have been isolated from water with a
temperature as high as 63oC and
the contamination is associated with other bacteria and protozoa.
Biofilms present on the internal surfaces of pipes can provide a means
of survival for Legionella bacteria and can interfere with efforts to
eradicate bacteria from water systems.
Correlation analyses suggest that a substantial proportion of
community acquired legionella infections may be residentially acquired
and associated with bacteria in hot water distribution systems.
Recently a study to assess the potential public health impact of
Legionella colonisation at a domestic level was undertaken in Italy.
146 samples were taken from domestic hot water systems in a range of
private homes in six Italian towns representing Northern, Central and
Southern Italy. Legionella species were detected in 33 (22.6%) of
samples.
Some factors associated with Legionella contamination were:
- a centralised water heater
- tank distance >10m from water point
- water plant age >10 years old
- zinc levels of <20µg/L and copper levels >50µg/L appeared to be
protective against Legionella colonisation.
Risk for legionellosis was retrospectively evaluated. The reported
frequency of pneumonia symptoms was double among persons living in
the legionella-positive homes compared to those living in the
legionella-free buildings. (8 cases in 95 residents vs. 15 from 333).
This difference however, is not statistically significant.
The researchers recommend simple and general measures to limit
Legionella colonisation at the domestic level:
- Use independent domestic water heaters
- Maintain high cleaning standards
- Periodically replace components of system which could favour
presence or dissemination of bacteria
- Maintain a water copper content >50µg/ml
The complete report on the study can be found at www.cdc.gov/eid
Emerging Infectious Diseases Vol. 10, No. 3, March 2004.
Cetec is experienced in correct water sampling techniques and can
sample the water from your hot or warm water system and conduct
analysis on the water chemistry and Legionella and bacterial content.
For more information about this article contact Cetec
here. |
