|
|
 |
|
|
|
Frequently Asked Questions from Professionals in
Engineering or Questions about drinking
water sources
Questions about non-potable water sources (cooling towers, whirlpools,
fountains).
What is the upper limit of Legionella for water distribution
systems? In contrast to the situation for cooling towers, there is solid scientific data
available for interpretation of culture results from hospital water
distribution systems. Risk assessment should not be based on the
concentration of Legionella recovered
from a given water outlet; quantitation (CFU/ml) does not correlate with incidence
of disease (CDC, Infection Control and Hospital Epidemiology 1999, Kohler,
Journal of Hospital Infection 1999, Pittsburgh Special Pathogens Laboratory [Best]
Lancet 1983). On the other hand, risk
for Legionella infections increase as
the extent of colonization with L.
pneumophila increases (i.e., a high percentage of water outlets yield Legionella). In two studies, Legionnaires’ disease did not
occur unless the percentage of water outlets reached 30% or greater (Best
Lancet 83, Stout, in press). Complete elimination of Legionella from a hospital water system
is not necessary to eliminate cases of Legionnaires’ disease in the hospital (Pittsburgh
Special Pathogens Lab [Stout], Infection Control and Hospital Epidemiology,
1998).
Can Legionella survive in chlorinated water?
Legionella has been isolated from chlorine treated
water. The levels of Legionella that elude the water treatment
process are essentially undetectable. When this water travels through the
system and loses much of the chlorine residual, either from retention time or
warm temperatures in water distribution systems, Legionella can then be
cultured. The colonization rate for large buildings is 20-70%, depending
on the geographic region. Residential water systems can also harbor Legionella. It is very interesting to learn from The Lancet Infectious Disease,
June 2003 article that virtually all outbreaks have been linked to potable
water, and that showering is not a mode of transmission (except perhaps for
high risk patients?). Showering
is allowed even for high-risk patients. Highly-immunosuppressed patients and
COPD (emphysema) patients should drink bottled water or boiled water that has
been cooled, but this is optional. If the percent of distal water sites is <
30%, we do not prohibit showering or drinking water for most patients even if Legionella is present in the water. See our reply to a question about
showering
in the FAQ from physicians. We have emergency shower/eyewash
combination units in our plant. The units are not used that much. I have heard
that the Legionella thrive in cooler water. Is this true and what measures can
we take to combat the problem? The emergency shower/eyewash units are fed
from the general potable water supply but are deadlegs as far as general system
flow patterns.
It is possible that Legionella might
be in these units, but the risk is negligible, and no infections have even been
reported to occur from use of these units.
No guidelines have ever been issued for such units and are probably
unnecessary. Emergency showers on water and waste water
sites - used for possible chemical splashes etc. Some of these showers have a
heated tank. Should these fall under the testing regime for Legionella?
The major mode of transmission of Legionella is aspiration (so drinking the
water is necessary), although intense aerosolization might transmit the
organism. In the emergency showers that you describe, the risk would be so low
as to not warrant any preventive measure. Should a water distribution system harboring Legionella anisa be
disinfected? The majority (>90%) of cases of
Legionnaires' disease reported in the
I´m a medical student at Karolinska Institute in Sweden currently
involved in a project about prevention of legionnaires disease, and I have
found your website to be a valuable resource.
I´m writing about the use of free radicals in the elimination of
legionella in water systems. Is this
something you are planning on evaluating?
The technique is very interesting and has been proven very efficient on
the elimination of Legionella species - among others - in water systems.
We are assuming you are speaking of the free
radicals of oxygen obtained by disinfecting with ozone or hydrogen
peroxide. We have not investigated hydrogen
peroxide in our laboratory. The Yamagiwa et al article presents a view of
hydrogen peroxide (Yamagiwa K, et al. (2001) Disinfection Kinetics of Legionlla
pneumophila by Hydrogen Peroxide.
Journal of Chemical Engineering of
I work for a building management company which involves controlling
domestic hot water tanks, I would like to know what the official minimum
storage temperatures are and the length of time they have to be at that
temperature. I am under the impression that it is a minimum temperature of 60oc
for at least 1 hour in any 24 hours (therefore the temperature can be dropped
for the remaining 23 hours) can you tell me if this is correct. The temperature should remain stable at
about 140oF at the tank. It
would not be wise to only hold this temperature for only one hour and then
reduce it. Please obtain a copy of the American Society of
Heating, Air Conditioning and Refrigeration Engineers (ASHRAE) guide to
"Minimizing the Risk of Legionella in Building Water Systems". This document has a section regarding hot
water storage temperature. You can also download a copy from the Baltimore
Aircoil web site (www.baltimoreaircoil.com). The "official" minimum storage
temperatures and durations may vary from In
the In
the Your suggestion of maintaining a water temp greater than 60oC
in the tank for 1 hour may kill Legionella in the tank; however, regrowth of
Legionella is likely to occur in the hot water distribution system where
temperatures could drop to less than 50oC depending on use. Ideally for Legionella disinfection you would
want to maintain a high temperature throughout the distribution system (hence
flushing).
Whatever heating regime you try, monitoring
of distal sites and the how water tank is necessary to document
the effectiveness of disinfection specific to your system and temperature set points.
We have had a copper-silver ionization
system on our hot water system for more than a year now. No cases of hospital-acquired Legionnaires’
disease have occurred since installation, but the copper and silver ion levels
are sometimes less than the recommended range by the manufacturer (copper
0.2-0.8 ppm; silver at 0.02-0.08 ppm (20-80 ppb). Is this cause for alarm or justification to
perform additional disinfection like a superheat and flush? Our experience indicates that ion levels
slightly below the manufacturer’s recommended levels are still effective in
systems that have been operational for awhile.
For example, we have had copper levels in the range of 0.1-0.2 ppm and
silver at 0.01-0.02 ppm (10-20 ppb). Our
environmental cultures remain well below our threshold of 30% positivity (0-10%
most of the time). I would request
either cleaning of the electrodes or adjustments in amperage if the level of
copper is at or below 0.1 ppm copper or 0.01 (10 ppb) silver. We would
not recommend that a decision to perform a superheat and flush be based on ion
levels. This procedure is labor intensive
and should be performed in response to either detection of a hospital-acquired
case of Legionnaires’ disease or an increase in colonization of the system to
30% or above. Questions about non-potable
water sources What is the acceptable upper limit of Legionella in cooling towers? We are skeptical that cooling towers are
a major source for disseminating Legionella
and we predict that many community outbreaks linked to cooling towers will
ultimately be shown to be from drinking water.
This is based on the fact that all hospital outbreaks originally linked
to cooling towers years ago are now known to have emanated from the hospital drinking
water. For more details, download the
following articles from our Publication section (Muder, Arch Int Med 86, Yu Am
J Med 93, Sabria Lancet Infect Dis 2002). Nevertheless,
because of concern about litigation involving Legionnaires’ disease, we receive
numerous inquiries about cooling tower maintenance. Moreover, many water treatment specialists
use the service of our Special Pathogens Laboratory for cultures of Legionella in cooling towers. Neither the Centers for Disease Control
(CDC) and Prevention nor the Environmental Protection Agency specify a minimum
contaminant level for Legionella for cooling towers. Outbreak
investigations have documented both low (<100 Colony Forming Units /mL) and
high (>1000 CFU/mL) levels of Legionella in water samples from
cooling towers. There are no scientifically based guidelines for establishing
risk criteria for Legionella recovery from cooling towers.
Although guidelines have been suggested from a few groups, the data used to
establish the relationship of the action levels to disease risk is very
limited. Therefore these guidelines are overly strict (recommending
remediation at lower levels) and should be interpreted with caution. Links to
various websites with guidance documents that suggest levels and interpretation
are available on our website by clicking onto “Research” and then “Other
Information”. The ASHRAE guidelines 12-2000 is available as a free download
from the Baltimore Air Coil website www.baltimoreaircoil.com. Are chlorine and other oxidizing biocides the only recommended
treatment for cooling towers? Click onto “Research” on the Home Page to see a table of
biocides that we and others have found to be effective. This table was published as part of the
American Society of Hospital Engineers technical document on Legionella. There are
effective non-oxidizing biocides. The
ASHRAE guideline (available at www.baltimoreaircoil.com)
does not recommend a specific biocide, but does recommend that you consult with
a water treatment specialist. If Legionella is found in decorative fountains, is remediation
needed? We would discourage the installation of
decorative fountains in hospitals. For
buildings that do not have persons at risk for pneumonia, the water fountains
can be treated with disinfectants such as chlorine or bromide. Ultraviolet
light may also be effective. Matt Freije
(www.hcinfo.com) recommends draining and
cleaning decorative fountains at least twice a year – or more often if slime or
dirt is visible. Surfaces can be scrubbed with a disinfecting solution (1 part
chlorine to 20 parts water may be appropriate).
Consult a water treatment service for advice. I am a journalist
working for Norwegian TV. In the city of
Public health authorities downplay the
significance of Legionella infections because most originate from drinking
water. It is easier to target a cooling tower and harder to discuss with the
general public the implications of Legionella in the drinking water. Note that the investigators said
"probably". All you have to do
is to ask the investigators
"Did you culture the homes of the patients and their workplaces for
legionella". If they refuse to answer, you will have learned something. See our recent
article Sabria Lancet Infectious Diseases, 2002 on our Home Page. There are a lot
of people who would like to believe that cooling towers are not sources for
Legionella infection. I'm sure ASHRAE would love to prove that and let the HVAC
design engineers off the hook. On the other hand if it's in the drinking water,
why did others in the Our views are accepted in the
scientific community. ASHRAE also is
aware of the data. However, the cooling tower link is so emphasized that it is
difficult for lay organizations and public health authorities to acknowledge that the scientific view has shifted. The Wadsworth VA Legionnaires’ disease
outbreak was initially linked to cooling towers by the CDC, but Legionella was
subsequently found to be in the drinking water due to the potable water (Shands
KN, JAMA 1985). Other Los Angles hospitals
specifically UCLA and Cedars-Sinai
hospitals also experienced unreported outbreaks linked to potable water. Cedars-Sinai and
The fact that it is in the drinking
water of homes and apartment buildings has been reported in the scientific
literature in many countries. Our studies were the first and the best-known
reports and can be downloaded from Publications in our website (see Coming of
the 3rd Plague on the Home Page). CDC also subsequently linked
drinking water to sporadic cases of Legionnaires’ disease (Straus W, Arch Int
Med 1996). Public health agencies are reluctant
to discuss this issue openly because of fear of panicking the population. Reports in You may want to read our perspective
in Stout, N Engl J Med We predict that most published reports
of cooling tower outbreaks will ultimately be shown to be erroneous. Virtually all the articles on hospital
outbreaks linked to cooling towers were published in the early 1980's.
Interestingly after we published the first report showing the real culprit was
drinking water in 1982 New England J Medicine and 1983 Lancet, subsequent
outbreaks have been linked to drinking water.
The most publicized cooling tower outbreaks involved cooling towers at
LA Wadsworth VA Medical Center, Rhode Island Hospital (Brown Univ), and Burlington
Hospital of U Vermont; the actual source is now known to be drinking water in
those hospitals. In the early days the
CDC never cultured the hospital water because they did not realize Legionella
could be there.
Allegheny County Guidelines
(which can be downloaded from the home page of www.legionella.org) recommended
culturing drinking water systems of hospitals, and disinfection, if necessary.
By 2001,19 In 1992, we reported that Legionella
could be contracted from the drinking water of homes and workplaces and warned
all public health agencies that before cooling towers were blamed, the homes
and the workplaces of the patients should be cultured to see if the real source
was the drinking water. CDC confirmed the
accuracy of our report to their surprise (Strauss, Arch Int Med 1996), but they
have not rescinded their cooling tower recommendations. And, cooling tower outbreaks in hospitals
have all but disappeared from the scientific literature. In a review of hospital
outbreaks since 1985, virtually all epidemiologic investigations now implicate
drinking water. What is the best procedure for preventing
Legionella becoming a
problem in Legionella must be in contact with the
active biocide (chlorine, bromine, etc.) for a sufficient amount of time and at
a concentration of the biocide that is active against Legionella. So, control of Legionella would occur in the
liquid phase. Maintain the biocide
concentration at the recommended level, monitor your biocide levels and keep
the system clean. This should keep your
system under We also believe some of the outbreaks
attributed to hot tubs were incorrect and the drinking water was the actual
source. If you have a question that has not been answered by the above answers,
click here to Ask
the Expert.
|
