Legionella
E-news -- 2
May 2000
Legionella
E-news, 2
May 2000
HC
Information
Resources
Inc.
Matthew R.
Freije,
Editor
**IN
THIS ISSUE**
1. Major
outbreak in
Melbourne
2. Food
humidifier
blamed for
South Wales
hotel
outbreak
3. Home
water
heaters
1.
MAJOR
OUTBREAK IN
MELBOURNE
Health
authorities
have
reported 46
cases of
Legionnaires'
disease
among
individuals
who visited
the new
Melbourne
(Australia)
Aquarium
between 11
and 21
April. A
47th case
involves a
26-year-old
man who had
walked near
the
building.
The count is
expected to
rise as
additional
laboratory
tests are
completed.
Nine
patients are
in critical
condition.
Two women,
ages 79 and
83, have
died. The
source of
contamination
has not been
confirmed,
but cooling
towers at
the aquarium
have been
disinfected
as a
precaution.
Health
authorities
suspect that
dust from a
nearby
construction
site could
have
contaminated
the towers.
Clive Broadbent
has been
hired to
conduct an
inspection.
Source: news
media
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2.
HUMIDIFIER
BLAMED FOR
SOUTH WALES
HOTEL
OUTBREAK
You may
remember
from the
last issue
of
Legionella
E-news that
a food
display
humidifier
was the
focus of the
investigation
of this
outbreak.
Evidence
suggests
that the
humidifier
was indeed
the source
of
contamination,
because the
strain of
Legionella
pneumophila
serogroup 1
found in the
two patients
who died
from
Legionnaires'
disease was
indistinguishable
from
isolates
found in the
food display
humidifier.
The
humidifier
was used to
produce mist
over food in
a
refrigerated
display
unit.
Source:
Eurosurveillance
Weekly;
reported by
Susan Hahné
and Roland
Salmon, CDSC
Wales, and
Arun
Mukerjee and
Bharat
Pankhania,
Bro Taf
Health
Authority.
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3.
HOME WATER
HEATERS
The
following
was
excerpted
and adapted
from our
upcoming
publication,
Home
plumbing
systems: How
to reduce
your risk of
Legionnaires'
disease:
Studies
indicate
that homes
with gas
water
heaters are
less likely
to have
legionellae
than are
homes with
electric
water
heaters. Of
the 211
homes
surveyed in
the Quebec
City area,
legionellae
were found
in none of
the 33
houses with
gas water
heaters but
were found
in 69 (33%)
of the 178
houses with
electric
water
heaters.(77)
Lee's
Pittsburgh
study also
showed a
significant
association
between
electric
water
heaters and
Legionella.(73)
In Stout's
study, which
found the
lowest
percentage
of
legionellae-positive
homes
overall
(6.4%), 207
of the 218
homes
examined had
gas water
heaters.(76)
Gas heaters
benefit from
the location
of their
heat source
below the
water tank.
Thus, the
bottom of
the tank,
where
sediment
accumulates,
is
sufficiently
hot to
prevent
legionellae
growth. In
contrast,
most
electric
units have
heating
elements on
the side of
the tank, so
the sediment
at the
bottom is
cool enough
to allow
legionellae
growth.(77)
In addition,
electric
water
heaters tend
to have
lower
temperatures
than do gas
heaters. In
the Quebec
City houses
studied by
Alary and
Joly, the
temperature
at the
faucets was
above 60°C
(140°F) in
most of the
houses with
gas or oil
heaters but
was between
50°C
(122°F) and
59°C
(138°F) in
most of the
houses with
electric
heaters.(77)
77.
Alary M. and
J.R. Joly.
"Risk
factors for
contamination
of domestic
hot water
systems for
Legionella."
Applied and
Environmental
Microbiology
57
(1991);2360-2367.
73.
Lee, T.C.,
J.E. Stout,
V.L. Yu.
"Factors
Predisposing
to
Legionella pneumophila
Colonization
in
Residential
Water
Systems."
Archives of
Environmental
Health 43
(1988);59-62.
76.
Stout, J.E.,
V. L. Yu,
Y.C. Lee, S.
Vaccarello,
W. Diven,
and T.C.
Lee.
"Legionella
pneumophila
in
residential
water
supplies:
environmental
surveillance
with
clinical
assessment
for
Legionnaires'
disease."
Epidemiol.
Infect. 109
(1992);
49-57.
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Copyright
2000, HC
Information
Resources
Inc.
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