ASHRAE Journal - April 2020 - 65

COLUMN HVAC APPLICATIONS

Legionella pneumophila was
present in 33% of sediments in
large storage tanks. Legionella DNA
was found in 67% of samples. No
Giardia DNA was detected.

C
D

In a study by the CDC, 32% of cooling
towers were contaminated with
Legionella pneumophila.3

It is likely that regrowth
of Legionella occurs in the
distribution system.1

33%
0%
Legionella Giardia
pneumophila

32%
Legionella
pneumophila

29% of cold-water tap samples were
contaminated with Legionella pneumophila;
results of an EPA study published in 2014.2

Significance
29%
Legionella
pneumophila

tested positive for Legionella pneumophila and 20% were
positive for serogroup 1 (Figure 1c).

Cooling Tower Study3

The drinking water storage tanks study found Legionella DNA
present in 67% of the samples, but no Giardia DNA was found.
* The lack of Giardia indicates successful disinfection at the
treatment plant.
* The high presence of Legionella indicates that methods used
to control Giardia completely fail to control Legionella.
The cold-water-tap study and the cooling water study each
yielded almost identical percentages of Legionella pneumophila
and Legionella pneumophila serogroup 1 contaminated samples as the storage tank study.
* The remarkable similarity of the results provides evidence
that the regrowth occurring in the distribution system is a
fundamental step in the chain of transmission, allowing infiltration into buildings where people are exposed.

The last key study took place in 2016, when the CDC
examined samples
TABLE 1 Summary data of studies.
taken from 196 cool% SAMPLES qPCR POSITIVE
% LOCATIONS qPCR POSITIVE
ing towers located in
Subject Reservoir Locations
Total Legionella spp.
Legionella Legionella pneumophila
Legionella pneumophila
most of the climate
Sampled Samples
pneumophila
serogroup 1
serogroup 1
zones of the United
Municipal Drinking Water
18
87
67%
33%
28%
Not Provided
States as defined by
Storage Tank Sediments
(58/87)
(29/87)
(24/87)
the National Oceanic
Cold Water Taps
68
269
Not Provided
29%
20%
47%
(77/269)
(53/269)
(32/68)
and Atmospheric
Cooling Towers
196
196
84%
32%
20%
20%
Administration
(164/196)
(63/196)
(39/196)
(39/196)
(NOAA). Using real
time qPCR testing, Legionella bacteria was detected in coolthe water treatment plant or in the distribution system,
ing towers located in each of the eight regions tested.
they will be present in the drinking water distribution
Legionella-positive samples were cultured and further
tested for specific DNA. Of 196 samples tested, 32% were supply with the potential to contaminate all water outlet
sources after entering the building water supply. (Table 1).
positive for Legionella pneumophila and 20% were positive
The results of this study should be very concerning to
for Legionella pneumophila serogroup 1. The test results
homeowners, commercial building owners, and facility
are almost identical to the tap water study, which is
managers of hospitals and hotels. The conclusion drawn
not surprising since cooling towers use tap water as
from this study is that the supply of fresh potable water
their fresh, potable makeup water source (Figure 1d).
entering their buildings is not consistently free of
Results and Significance
pathogens. This is not surprising considering the weak
The similarities between results from the three studies
antimicrobial efforts used at the water treatment plant
indicate that when Legionella bacteria are not addressed at and in the drinking water distribution system.
APRI L 2020

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ASHRAE JOURNAL

65


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ASHRAE Journal - April 2020

Table of Contents for the Digital Edition of ASHRAE Journal - April 2020

Contents
ASHRAE Journal - April 2020 - Intro
ASHRAE Journal - April 2020 - Cover1
ASHRAE Journal - April 2020 - Cover2
ASHRAE Journal - April 2020 - 1
ASHRAE Journal - April 2020 - Contents
ASHRAE Journal - April 2020 - 3
ASHRAE Journal - April 2020 - 4
ASHRAE Journal - April 2020 - 5
ASHRAE Journal - April 2020 - 6
ASHRAE Journal - April 2020 - 7
ASHRAE Journal - April 2020 - 8
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ASHRAE Journal - April 2020 - 10
ASHRAE Journal - April 2020 - 11
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ASHRAE Journal - April 2020 - 14
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ASHRAE Journal - April 2020 - Cover3
ASHRAE Journal - April 2020 - Cover4
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