Environmental Engineering Reference
In-Depth Information
occurs sporadically, affecting single individuals. Approximately 25% of
reported cases occur in hospital patients, with about 75% of cases being
community-acquired.
The causal agents of Legionnaires' disease are species of bacteria com-
monly found in freshwater environments (circa 20 to 25% of samples are
positive). There are approximately 17 species of the genus
Legionella
that
cause human disease, with
being responsible for approxi-
mately 80% of the 1000 or so cases reported annually in the U.S.
Members of the
L. pneumophila
genus are Gram-negative, aerobic, rod-shaped
bacteria that live as facultative intracellular parasites in other aquatic micro-
scopic organisms. Because of its relative tolerance to chlorine,
Legionella
L. pneumophila
is commonly found in potable water systems.
species grow well at elevated temperatures (circa 35°C). As a
consequence, abundant populations are common in the waters of cooling
towers and evaporative condensers, hot water heaters, whirlpools, spas, and
hot tubs.
Legionnaires' disease appears to be an opportunistic infection since host
risk factors play an important role in development of the disease. Risk
factors include tobacco smoking, alcohol consumption, middle age, male
gender, preexisting lung disease, diabetes, AIDS, immunosuppressive ther-
apy, and travel.
The primary route of infection is inhalation exposure to aerosols pro-
duced by
Legionella
Legionella
-contaminated water. Though there is a potential for expo-
sure to
in residential and motel/hotel room showers, such expo-
sures have yet to be documented and reported. They have been documented
in hospitals, where control of
Legionella
Legionella
is a major infection control concern.
Pontiac fever is a nonpneumonic, self-limiting (2- to
3-day duration), influenza-type illness apparently caused by exposure to
certain strains of
d.
Pontiac fever.
. The attack rate is approximately 95% com-
pared to 5% for Legionnaires' disease. Pontiac fever, unlike Legionnaires'
disease, is not fatal.
The disease was first identified a decade after a major outbreak occurred
among health department employees in Pontiac, MI. Analysis of preserved
blood samples indicated that both Pontiac fever and Legionnaires' disease
shared the same etiological agent. Symptoms consist of fever, chills, head-
ache, and myalgia. After initial illness, affected individuals do not become
symptomatic again. In the first documented case, the source of exposure was
believed to be an evaporative condenser whose aerosol became entrained in
the building's air handling system. Other outbreaks have been reported in
an office building, an automobile assembly plant, and among maintenance
workers inside a steam turbine condenser. Based on the relatively few reports
in the scientific literature, Pontiac fever is either rare or rarely diagnosed.
Pontiac fever appears to be associated with large numbers of dead bac-
terial cells or cells with reduced virulence that cannot produce sustained
growth in the lungs.
L. pneumophila
