Legionnaires Disease: An Overview - Saudi Aramco

Legionnaires Disease:
An Overview
Gareth W. Watts, Environmental Protection Department
Legionnaires’ disease is an uncommon but potentially fatal form of pneumonia,
principally caused by the bacterium Legionella pneumophila. There are 50
species of legionellae, which all have the potential to cause disease. Legionella
pneumophila accounts for about 90% of the cases. The collective term used
to cover the group is legionellosis. The majority of cases are isolated, but there
have been many reported outbreaks around the world, where a common
community source is implicated, for example, a cooling tower.
Person-to-person spread of the disease does
not occur, and not everyone exposed will
develop symptoms. To contract the disease
the bacteria must be inhaled deeply into
the lungs, via an aerosol (

cooling towers were poorly disinfected and
contaminated with Legionella pneumophila.
In 2002, there was an outbreak traced to a leisure
center cooling tower in the town of Barrow-in-
Furness in the north of England; this resulted in the
deaths of seven people and infected a further 180.
The Disease
70 °C Rapid kill to 100%
60 °C 90% killed in 2 minutes
50 °C 90% killed in 2 hours
45 °C
Bacteria
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Symptoms of Legionnaires’ disease include
anorexia, malaise and lethargy; fever is present in
almost all cases, and if untreated, worsens during
the first week and can be fatal. Complications can
include respiratory failure, shock and acute renal
and multi-organ failure. Appropriate early antibiotic
treatment usually results in full recovery. In severe
infections, there are often general secondary
symptoms, such as weakness, poor memory and
fatigue, these can last for several months.
During the period 2005-2006 across 35 European
countries, there were 11,900 reported cases
attributable to legionellosis resulting in 377 deaths.
The total number of cases is generally believed to
be underestimated due to misdiagnosis. Some 20%
of the cases of legionellosis detected in Europe are
thought to be related to travel.
How it is Spread
Water is the major reservoir for legionellae and it
is found worldwide in many different natural and
artificial aquatic environments, such as cooling
towers; water systems in hotels; water irrigation
systems; domestic properties; ships and factories;
the surface of respiratory therapy equipment;
ornamental fountains; misting devices, and spa
pools.
20 °C Bacteria remains
dorman but viable
Legionella bacteria also require a supply of nutrients
to multiply, and the presence of sediment, sludge,
scale and other material within a water system,
together with bio films, play an important role in
harboring and providing favorable conditions for
growth.
It is important to control the risk from exposure to
legionella bacteria by introducing measures which
do not allow growth in water systems, and reduce,
so far as is reasonably practicable, exposure to
inhalable water droplets.
Water Temperature’s Impact on
Legionnella Pneumophila
The bacteria can survive under a wide variety of
environmental conditions and have been found in
water at temperatures between 6 ºC and 60 ºC.
Research suggests that water temperatures in the
range of 20 ºC to 45 ºC favor growth. The organisms
do not appear to multiply below 20 ºC and will not
survive above 60 ºC. They may, however, remain
dormant in cool water and multiply only when
water temperatures reach a suitable level.
Fresh drinking water distribution systems are
likely to contain some microorganisms, including
legionellae. Factors that can promote growth
include temperature, water quality, design, material
used in construction and the presence of bio films.
Control measures range from protecting the water
source from contamination, effective treatment,
and design of systems to prevent stagnation and
control of temperatures.

“The disease was first
identified in 1976, following a
large outbreak of pneumonia
among people attending an
American Legion Convention
at the Belle Vue Stratford
Hotel, Philadelphia. The disease
affected 221 people, resulting in
34 deaths.
”
Showers are often mistakenly believed to be the
only source of aerosols linked to health care setting
legionellosis, however, water outlets, humidifiers,
respiratory devices and nebulizers that have been
filled or cleaned with tap water can also spread
Legionella and have been reported as a source of
infection in several cases.
Cooling towers and evaporative condensers
have been implicated in numerous outbreaks
of Legionnaires’ disease. The major risk appears
to be neglect or insufficient maintenance, or the
start up of stagnant systems without adequate
chemical treatment. Cooling towers need an
effective water treatment program to control
fouling and corrosion.
Ships, including cruise liners, coastal tankers and
passenger ferries also present risks as they are
closed environments, and hot and cold water
systems have been implicated in a number of
outbreaks. In 1998, an outbreak on a cruise ship
that sailed to the Mediterranean and the Norwegian
fjords found showerheads contaminated with
legionella bacteria. (Arthur, 1998). In June 2001,
two mechanics working on a cargo ship’s water
system in Spain died after contracting Legionnaires’
disease.
While there have been no recorded outbreaks of
Legionnaires’ disease associated with bathing in
swimming pools, they have been associated with
hot tubs, display spas and Jacuzzis. This is due to
warm water temperature, high bather density,
conditions for nutrient growth, and the potential
to inhale aerosols due to close contact with the
water surface. Design, installation, management,
and effective disinfection of these water systems
must be undertaken to control Legionella.
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EnviroNews
Other systems implicated in the spread of
legionellosis via aerosols include domestic plumbing
systems, misting devices associated with food
displays, natural thermal springs and thermal spas.

the open air outside the tower, unless appropriate
controls are in place. Even with appropriate design
and under normal operation, some water droplets
that are small enough to be inhaled can leave the
drift eliminator.
Protecting Ourselves
EnviroNews
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Issue No. 20 – Winter 2011/12
Cooling towers and evaporative condensers
move large quantities of air, and are excellent air
scrubbers or washers. However, dirt, dust, and
other particulate matter will enter the cooling
tower water in the evaporative cooling process, and
water droplets that have been generated within
the plant and carried in the airflow, termed “drift,”
will contain dissolved salts, suspended particles and
bacteria that were in the original water. Diverse bio
films, which can support the growth of legionellae,
may be present on all wet surfaces throughout the
system; for example, on heat exchangers, the fill,
the sump and pipes. These droplets can create an
infectious aerosol when the water evaporates in
References and Further Reading
The hazard from Legionellosis should not be
underestimated; it presents a serious threat to public
health, and has to be carefully controlled as part of
a risk-based approach, by a multi disciplinary team,
bringing together expertise from engineering,
public health, epidemiology and water treatment
specialists. Regular testing for Legionella bacteria
in water systems should form part of an overall
comprehensive risk assessment.
The Environmental Protection Department (EPD)
has been working with a number of Saudi Aramco
proponents to raise awareness of the risk to health
from this infection. A pilot study was recently
carried out by EPD at a number of Company assets,
both onshore and offshore, to determine the
extent of potential contamination with Legionella
bacteria. Results were negative, which indicated
that adequate controls are in place.
Arthur, J. (1998). EHO’s Steer cruise ship from unsafe waters. Environmental Health, 106 (10): 285-288.
Bhopal, R. (1995). Source of infection of sporadic Legionnaire’s disease; a review, Journal of Infection,
30:9-12.
EWGLINET (European Surveillance Scheme for Travel Associated Legionnaires Disease) (2003). European
guidelines for control and prevention of travel associated Legionnaire’s disease. EWGLI.
HSC (Health and Safety Commission, U.K.) (2000). Legionnaire’s disease. The control of legionella
bacteria in water systems. Approved code of practice and guidance. Norwich. HMSO.
WHO (2007) Guide to Ship Sanitation, 2nd Ed Geneva, WHO.
WHO (2007) Legionella and the prevention of legionellosis, Geneva, WHO.