|Microb Ecol 1996 Jul;32(2):203-228
Ecology of Legionella: From Data
to Knowledge with a Little Wisdom.
Savannah River Technology Center,
Savannah River Company, Aiken, SC 29808, USA
The respiratory diseases produced
by the Legionella genus of bacteria are collectively called Legionellosis.
Presently more than 34 species of Legionella have been identified, 20 of
which have been isolated from both environmental and clinical sources.
The diseases produced by Legionella include the pneumonic form, Legionnaires'
disease, and the flu-like form, Pontiac fever. Because the vast majority
of Legionellosis is caused by the L. pneumophila species, this bacterium
is the thrust of the discussion.Legionella is a global bacterium.
The relationship of the bacterium to its environment has told us many things
about infectious diseases. Not until Legionellosis and the discovery of
its etiologic agent, Legionella, has such a successful modern-day marriage
been consummated between the agent and its environment.
Nearly two decades have passed since the term Legionellosis found its way
into the vocabulary of the scientific journals, the popular press, and
courtroom proceedings. Too often the scientific development, engineering
implementation, and societal acceptance are disconnected.
The focus scientific research sometimes does not reflect engineering or
societal needs and thus contributes little to the solution of immediate
and important problems. At other times, scientific knowledge that could
contribute to solutions is overlooked because of poor communication between
the problem holders, the scientific community, regulatory agencies, the
problem makers, and the public. The scope of this paper provides insights
on the ecological niche of Legionella, describes the organism's ecological
relationships in the natural world, and
The epidemiology of Legionella
Doebbeling BN; Wenzel RP
Department of Medicine, University
of Iowa Hospitals and Clinics, Iowa City.
Semin Respir Infect, 2: 4, 1987
The study of outbreaks of Legionella
pneumophila has been essential in understanding the organism, the disease,
and its pathogenesis. Early epidemics defined the clinical spectrum: Pontiac
fever is an acute, self-limited, febrile illness with an attack rate of
95% to 100% and an incubation period of 36 hours. In contrast, legionnaires'
disease is a life-threatening bronchopneumonia with an attack rate of 2%
to 7% and an incubation period of two to ten days.
Three times as many males as females are affected with legionnaires' disease,
and age, cigarette smoking, and chronic medical disease (particularly immunosuppression)
appear to be separate risk factors. Furthermore, L pneumophila is responsible
for approximately 1% to 3% of community-acquired pneumonias, 13% of those
acquired in the hospital and as many as 26% of atypical pneumonias. Diverse
environmental reservoirs have been identified, including cooling systems,
potable or domestic water systems, respiratory therapy devices, industrial
coolants, and whirlpool spas. Hot water temperature, stagnant water, sediment,
and the presence of other microorganisms are important factors in the amplification
of the Legionellaceae.
Although airborne transmission has been widely suggested, aspiration may
be an important mode in certain patients. Regional and national surveillance
may identify common sources and allow the introduction of early control
measures. The latter have included primarily pulse and continuous hyperchlorination
and super-heating hot water systems to 50 to 60 degrees C. Experimental
data suggest that ozone and UV light may be useful in the future. Additionally,
cooling towers and evaporative condensers have been decontaminated and
maintained with a variety of biocides. The
prevention of outbreaks requires thoughtful planning, redesign, and good