March 31, 1987

                               Health Advisory
                           Office of Drinking Water
                     U.S. Environmental Protection Agency

     The Health Advisory (HA) Program, sponsored by the Office of Drinking
Water (ODW), provides information on the health effects, analytical methodology
and treatment technology that would be useful in dealing with the contamination
of drinking water.  Most of the Health Advisories prepared by the Office of
Drinking Water are for chemical substances.  This Health Advisory is different
in that it addresses contamination of drinking water by a microbial pathogen
and examines pathogen control rather than recommending a maximum allowable
exposure level.  Thus,  for a variety of reasons, the format and contents of
this Health Advisory necessarily vary somewhat from the usual Health Advisory

     Health Advisories serve as informal technical guidance to assist Federal,
State and local officials responsible for protecting public health when
emergency spills or contamination situations occur.  They are not to be
construed as legally enforceable Federal standards.  The HAs are subject to
change as new information becomes available.

         This Health Advisory (HA) is based upon information presented in the
Office of Drinking Water's Criteria Document (CD) for Legionella.  Individuals
desiring further information should consult the CD.  The CD is available for
review at each EPA Regional Office of Drinking Water counterpart (e.g., Water
Supply Branch or Drinking Water Branch), or for a fee from the National
Technical Information Service,  U.S.  Department of Commerce, 5285 Port Royal
Rd., Springfield,  VA 22161, PB # 86-117843/AS.  The toll-free number is (800)
336-4700; in the Washington, D. C.  area:  (703) 487-4650.

         Legionellae are bacteria that have been identified as the cause of
legionellosis.  Based upon an attack rate of about 1.2 cases of legionellosis
per 10,000 persons per year (Foy et al., 1979), it has been estimated that
more than 25,000 cases of this disease occur annually within the United
States, and are caused primarily by one of the 23 currently recognized species
of the genus Legionella.  Most people who have developed Legionnaires Disease,
the pneumonia form of legionellosis, were immunosuppressed or appeared to be
more susceptible because of an underlying illness, heavy smoking, alcoholism,
or age (more than 50 years old).  In contrast, while some apparently healthy
individuals have developed Legionnaires Disease, outbreaks involving healthy
people have been limited mostly to the milder non-pneumonia form of the
disease called Pontiac Fever.

     Legionellae are widespread in lakes and rivers (Fliermans et al., 1979,
1981).  There is some indication that these organisms may be either very
sparse or absent in groundwater (Fliermans et al., 1982; Spino et al., 1984).
Spino et al. (1984) was unable to isolate legionellae after aeration of
groundwater through a redwood-slat aerator.  The possibility that humans may

Legionella                                                       March 31,  1987

    be exposed transiently to legionellae because of their high rate of contact
    with water is highly probable, given the high frequency of seropositivity to
    legionellae in healthy populations (Wentworth et al.,  1984) and the widespread
    occurrence of legionellae in water environments.

         In a number of outbreaks of legionellosis that have occurred in the
    United States, aerosols of water documented to contain the specific type of
    legionellae that was recovered from the patient have been identified as the
    vehicle for transmission (Cordes et al., 1981; Stout et al., 1982; Garbe
    et al., 1985).  It has been hypothesized that legionellae enter buildings
    in very low numbers via the treated drinking water.  These bacteria may
    proliferate in warm water when factors not yet fully determined allow them.
    Even when this occurs, as has been shown in numerous buildings, disease
    usually does not result.  Cases and outbreaks of legionellosis occur only
    when aerosols containing legionellae possessing specific virulence factors
    (not as-yet determined) are inhaled (possibly ingested) by susceptible
    individuals.  Foodborne outbreaks or secondary spread have not been reported.

         This Health Advisory discusses the control of legionellae in drinking
    water.  This includes finished water at the treatment facility, the distri-
    bution system, and plumbing systems.  Plumbing systems include hot water
    tanks, taps, showerheads, mixing valves, the faucet aerators,  all of which
    have been associated with the proliferation of legionellae.  This guidance
    does not discuss legionellae control for whirlpools, respirators, or heat-
    rejection equipment such as cooling towers and air conditioners.  These have
    all been associated with cases of Legionnaires Disease.

    Presence of Legionellae in the Distribution System and Plumbing Systems

         Legionellae are found in raw water, in treated waters, and in plumbing
    systems (Fliermans et al.,  1981; Hsu et al., 1984; Witherell et al., 1984),
    but the occurrence and fate of these organisms in the distribution system
    between these points are unknown.  The organism may survive the treatment
    and disinfection process and pass intact through the distribution system.
    In addition, opportunities  exist for their introduction into the system by
    means of broken or corroded piping, repair of existing mains,  installation of
    new mains,  back siphonage and cross connections,  any of which  may result in
    contamination of the water supply.  In older distribution systems, especially
    those dependent on gravity  flow, deterioration of piping may be so severe
    that the treated water comes in intimate contact with soil and is subject
    to infiltration by surface  water.  Thus, legionellae may be introduced into
    potable water by these routes.

         Legionellae surviving initial water treatment may colonize pipe joints
    and corroded areas or adhere to the surface or sediment of storage tanks,
    especially  those constructed of wood.  Here, they may  find a habitat suitable
    for survival and growth (Engelbrecht, 1983).  Cul-de-sacs, intermittently
    used storage tanks and other sites in which waterflow is absent or restricted
    also may be appropriate habitats for legionellae.

         New distribution systems or their components that were not appropriately
    cleaned and disinfected before being put into use may  introduce legionellae
    into the system.  Although  this has not been documented, it may not be

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    coincidence that some of the serious outbreaks of Legionnaires Disease have
    occurred in newly-opened institutions or buildings (Haley et al., 1979; Marks
    et al., 1979; Helms et al., 1983).  Construction activities may have included
    intervention into the water supply mains with introduction of contaminated
    water or,  possibly, disturbance of sediment and sloughing of scale bearing
    high concentrations of legionellae by means of hydraulic shock or other

         There are numerous reports of legionellae occurring in plumbing systems,
    especially in hot water systems.  Most of these investigations have been
    carried out in hospitals,  and many were prompted by outbreaks of nosocomial
    (hospital-acquired) Legionnaires Disease.  The primary reservoirs in hospitals
    are apparently hot water tanks in which water is maintained at temperatures
    below 55C.  Legionellae also have been found in showerheads, rubber fittings,
    aerator screens, faucet spouts, and other plumbing fixtures.  This group of
    organisms has also been found in residential plumbing systems such as apartment
    buildings  and homes (Wadowsky, 1982; Arnow and Weil,  1984), but disease has
    not been associated with these findings.

    Control at the Water Treatment Facility

         Only a few studies have been published on the effectiveness of various
    types of treatment for eradicating or reducing legionellae numbers at the
    water treatment utility.  In one study, Tison and Seidler (1983) examined raw
    water and three kinds of distribution water supplies:  (1) those treated by
    chlorine (free residual 0.2-0.6 mg/L); (2) those treated by sand filtration
    and chlorination (free residual 0.0-0.4 mg/L); and (3) those treated by
    flocculation, mixed media filtration, and chlorination (free residual
    0.572.0 mg/L).  Legionella were enumerated by direct fluorescent antibody
    (DFA) tests and all distribution waters contained about one order of magnitude
    fewer Legionella-like cells than did the raw waters,  i.e., 103-104 per liter.
    While the  evidence suggests that legionellae are common in treated water, the
    significance of. these results is questionable because the authors were unable
    to isolate any legionellae by animal inoculation or culture procedures, and
    there are  uncertainties about the specificity of the DFA technique used for
    legionellae detection.

         Most  water treatment plants in the United States use chlorine disinfection.
    Although extrapolation of laboratory studies to treatment plant situations is
    somewhat tenuous,  Kuchta et al. (1983) reported that both L_. pneumophila and
    L_. micdadei (laboratory-adapted environmental and clinical strains) were much
    more resistant to chlorine than was Escherichia coli.  At 21C, pH 7.6, and
    0.1 mg/L of free chlorine residual, a 99 percent kill was achieved in less
    than one minute for IS. coli compared to 40 minutes for L_. pneumophila.  Under
    the same conditions,  0.5 mg/L of free chlorine resulted in a 99.9 percent
    legionellae kill in about 5 minutes.  The contact time for a 99 percent kill
    of L_. pneumophila at 4C was twice as long as it was  at 21 C.  The authors
    concluded  that legionellae can survive low levels of chlorine for rather long
    periods of time.  In a subsequent study,  Kuchta et al. (1984) compared agar-
    passaged (laboratory-adapted) and tap water-grown strains of L_. pneumophila
    with respect to chlorine resistance,  and showed that the latter were consid-
    erably more resistant.  At 0.25 mg/L free residual chlorine, 21C, and pH
    7.6-8.0, a 99 percent kill of agar-passaged L_. pneumophila was usually

Legionella                                                       March 31,  1987

    achieved within 10 minutes, compared to 60 to 90 minutes for tap water-
    maintained strains.  These data suggest that normal chlorination practices
    at treatment facilities may not control legionellae.

         In contrast to these data, Hsu et al. (1984) reported that survivals of
    L_. pneumophila and J2. coli in various concentrations of chlorine were similar.
    In an in vitro study, laboratory-adapted strains of L_. pneumophila Flint 1
    serogroup 1 and J3. coli B were inoculated into several dilutions of sodium
    hypochlorite in sterile tap water,  and incubated at 24C.  At 0.2 mg/L residual
    chlorine, about an order of magnitude reduction occurred in two hours for both
    organisms.  Neither organism could be recovered after two hours at concentrations
    equal to or exceeding 2.0 mg/L.  The pH values were not reported.  The reason
    for the discrepancy between this study and the Kuchta et al. (1983, 1984)
    studies may be due to strain or pH differences.

    Control of Legionellae in Plumbing Systems

         Chlorine and Heat

         Studies on controlling legionellae in plumbing systems have examined
    primarily the effectiveness of heat and chlorine.  The results of several of
    these are described below.

         In an attempt to eradicate L^.  pneumophila from showers in a transplantation
    unit experiencing cases of Legionnaires Disease, Tobin et al. (1980) emptied
    the hot and cold water tanks and filled them with water containing 50 mg/L
    free chlorine.  After three hours,  this process was repeated.  Shower fittings
    were removed and held at 65C for 18 hours before replacement.  Legionellae
    were not isolated from the shower samples after six months, but were found
    again at nine months.

         Massanari et al. (1984) controlled a nosocomial outbreak of L. pneumophila
    infection by shock chlorination (15 mg/L) of both hot and cold water supplies
    for 12 hours.  The system then was flushed and the hot water temperature
    raised from 41C to 64C for 41 days.  These measures significantly reduced
    the frequency of positive cultures,  but 3/35 of the outlets were still positive.
    Thereafter, a continuous-flow proportional chlorination unit was installed
    that provided free chlorine levels  of 8 and 7.3 mg/L in hot and cold water,
    respectively.  During the first 16 months of its use, virtually no samples
    (N=355) contained 1^. pneumophila and no new cases of legionellosis were
    identified.  The few positive samples were obtained from rooms which had been
    vacant for at least 32 days.  In this hospital, water is distributed in
    copper pipes.

         Baird et al. (1984) hyperchlorinated their hospital water supply at a
    constant level of 4 mg/L of free chlorine.  The rate of nosocomial Legionnaires
    Disease decreased by almost two-thirds and the total numbers of legionellae
    decreased, but the organisms persisted.

         Witherell et al. (1984) attempted to eradicate L_. pneumophila in hospital
    plumbing by adding chlorine to the cold water make-up that supplied the hot
    water heating system, in proportion to the water demands on the system.  This
    was to avoid corrosion damage resulting from constant feed chlorination units

Legionella                                                   March 31, 1987

during periods of low demand.  A free chlorine residual of 3.0 mg/L was
maintained in the hot water system for 10 days and then reduced to 1.5 mg/L.
The organism was not detected by direct culture methods subsequent to disin-
fection.  The corrosivity of the hot water increased slightly (Langelier
index = -0.3).

     Fisher-Hoch et al. (1981) used hypochlorite to obtain a level of
1-2 mg/L of free chlorine at all cold water outlets in Kingston Hospital
where legionellae were present in both cold and hot water.  The free chlorine
levels in the hot water could not be maintained above 0.2 mg/L and legionellae
were recoverable at this level.  The water temperature was 45C, which was
warm enough to volatilize the chlorine and cool enough to allow growth of
legionellae.  Eradication was accomplished successfully by maintaining the
hot water temperature at 55-60C, in addition to disinfection of cold water.
Subsequently, these investigators reported that when a disconnected hot water
tank containing stagnant water was turned on again, _L. pneumophila was found
in the water and a case of nosocomial Legionnaires Disease occurred (Fisher-Hoch
et al., 1982).  A second disconnected tank which had been drained incompletely
contained a thick brown liquid deposit at the bottom.  This deposit contained
5.4 x 108 L* pneumophila/L.  Filling the second tank with water containing
50 mg/L of chlorine for 24 hours followed by descaling did not successfully
eliminate the legionellae.  Maintaining a constant water temperature of 70C
throughout the tank for 1 hour, however,  eliminated the organism.  Ciesielski
et al. (1984) also noted that legionellae can proliferate in stagnant water
inside hot water tanks.

     Dennis et al. (1982) examined water samples from the plumbing of 52
hotels, none of which was associated with cases of legionellosis.  Ten
isolates of L^. pneumophila were obtained from water samples from eight hotels.
Seven of these were from hot water taps or hot-cold mixer showers with water
temperatures ranging from 40 to 54C at the time of sampling.  Evidence that
these temperatures are not sufficient for Legionella control was also provided
by Meenhorst et al. (1983).  In their study, guinea pigs exposed to aerosolized
legionellae from contaminated hot tapwater (48C) contracted pneumonia.  The
strain of L_. pneumophila used was isolated from a series of patients in the

     Beam et al. (1984) attempted to control legionellosis outbreaks in two
state development centers for the severely handicapped.  In one center, hot
water tanks that were positive for legionellae were heated to 71C for 72
hours, followed by flushing for 15 minutes.  Because of legionellae regrowth,
a monthly heating schedule was established.  Subsequently, the chlorine level
was raised from 0.5 mg/L to 2 mg/L.  This approach was successful in eradi-
cating legionellae from water sources, but this chlorine level caused leaching
from the iron pipes and consequent discoloration of the water, and was thus
discontinued.  Cement liners were installed in the hot water tanks and the
first samples were positive for legionellae.  The water temperature was not
reported.  Soon after, an outbreak of legionellosis occurred.

     Plouffe et al. (1983) examined the relationship between the presence of
L^. pneumophila in potable water, nosocomial Legionnaires Disease, and hot
water temperatures in six buildings.  _L.  pneumophila was found in the hot
water of all four buildings in which hot water was maintained at 43-49C

Legionella                                  ,                 March 31, 1987

(110-120F), and nosocomial Legionnaires Disease was found in three of these
buildings.  No organism and no disease was found in the two buildings where
hot water was maintained at 57-60C (135-140F).  When the plumbing system
of one of the buildings experiencing both L_. pneumophila and Legionnaires
Disease was flushed with 71C water and the hot water then maintained at
57-60C, no L_. pneumophila and no new cases of Legionnaires Disease occurred
for at least six months.  The authors concluded that colonization and nosocomial
Legionnaires Disease can be prevented by maintaining the hot water at 57-60C.

     In another attempt to eradicate L. pneumophila and nosocomial Legionnaires
Disease, Yu et al. (1982) raised the temperature in the hot water storage
tanks from 45 to 60C for 72 hours and flushed 50 showers and 360 faucets
for 20 minutes with the 60C water to eliminate the organism from the sediment.
A substantial reduction in counts occurred.  After three months, colony counts
increased rapidly from four colonies/mL to over 300 colonies/mL and nosocomial
Legionnaires Disease again appeared.  The authors concluded that a periodic
schedule of short-term temperature elevation of the hot water system may
control nosocomial Legionnaires Disease.

     Stout et al. (1986) tested 75 legionellae isolates for their ability to
withstand high temperatures.  Tubes containing buffered yeast extract broth,
sterile water, or hot water tank water plus sediment were inoculated and
placed in 60C, 70C or 80C water baths.  At 60C, four minutes were required
for a one log reduction of L. pneumophila in the water plus sediment tube.
Approximately 25 minutes were required at this temperature to sterilize a
suspension of _L. pneumophila which contains 108 colonies/mL.  The authors
recommend that when flushing distal outlets, that a flush temperature exceeding
60C should be maintained for at least 30 minutes.

         Muraca et al. (1987) compared the relative efficacies of heat
(60C), ozone (1-2 mg/L), UV (30,000 uW-scm2 at 254 nm) and hyperchlorination
(4-6 mg/L) to eradicate 1^. pneumophila in a model plumbing system.  Non-turbid
water at 25C and 43C and turbid water at 25C were tested.  When samples
were taken of the circulated water, a 5-log kill of a 107 bacteria/mL concen-
tration was achieved with all treatments within six hours.  However, it is
noteworthy that heat completely eradicated the Legionella in less than three
hours, whereas UV light had produced its 5-log decrease in 20 minutes and
no further inactivation was seen during the six-hour observation period.
Chlorine and ozone required five hours to effect a similar 5-log decrease and
chlorine achieved complete eradication only in the non-turbid samples during
the six hours, while ozone killed the organisms in both turbid and non-turbid
water in four to five hours.

     Ozone Treatment

     Edelstein et al. (1982) used ozone in an attempt to eradicate legionellae
from the potable water supply of an unused wing of a hospital that was known
to be contaminated with bacteria.  The results were inconclusive because the
organisms were eliminated from both the experimental wing and the control
wing that was untreated.  The latter was thought to be due to excess mechanical
flushing and an unexpected rise in the chlorine content of the main water supply.
The in vitro susceptibility of L_. pneumophila to ozone was on the order of
0.36 mg ozbne/L, but was not consistent.  The ozone mean residual concentration
used in the hospital water system was 0.79 mg/L.

Legionella                                                   March 31, 1987


     Ultraviolet Radiation Treatment

     Antopol and Ellner (1979) reported that 90 percent of L_. pneumophila
cells in distilled water were killed by 920 microwatt-sec/cm2 of UV radiation.
This could be compared with exposures ranging from 2,100 to 5,000 microwatt-
sec/cm2 for killing of E. coli, Salmonella, Serratia and Pseudomonas.  If
the latter values were obtained under the same conditions as those used for
Ij. pneumophila, it would indicate that legionellae may be more than twice as
susceptible to UV radiation than are the other organisms.

     Gilpin (1984) reported laboratory and field experiments using UV radiation
to inactivate Legionella spp. in standing and recirculating water systems.
Times of exposure to one microwatt/cm2 of UV radiation to produce 90 percent
killing of six species of Legionella ranged from 17 to 44 minutes.  A commer-
cial UV apparatus killed 99 percent of the organism in less than 30 seconds
in a three-liter recirculating water system.

     In addition, Knudson (1985) reported that when agar plates seeded with
^. pneumophila were exposed to 240 microwatt/cm2 for 25 seconds or less, a
reduction of six to seven orders of magnitude was observed.  However, when
UV-irradiated legionellae were exposed to indirect sunlight for 60 minutes,
the recovery rates were two orders of magnitude greater than those not exposed
to sunlight, due to photoreactivation.

     Ethylene Oxide Treatment

     Cordes et al. (1981) sterilized Legionella-contaminated showerheads with
ethylene oxide but they were soon recontaminated.

Design of Hot Water Tanks

     Legionellae often have been reported in hot water tanks, particularly in
the bottom sediment.  The design of these tanks is important in the control
of these bacteria.  Most residential hot water tanks are heated from the
bottom near the cold water entrance pipe and are more likely to maintain a
bottom temperature high enough (>55C) to prevent growth of legionellae.
However, if thermostats in homes have been set low (<55C) as an energy
conservation measure,  growth of legionellae may result.  Thermostats for hot
water heaters in hospitals and other health care facilities are usually set
at lower temperatures in conformity with the recommendations of the Joint
Commission on Accreditation of Hospitals that the water temperature be "safe"
(JCAH,  1985).  This practice,  which is done to prevent scalding of patients
using the hot water, may promote the growth of legionellae.  Larger institu-
tional tanks also are heated more often by internal steam coils or by other
heaters located midway from top to bottom of the tank.  The water at the
bottom may not be heated sufficiently to kill legionellae.  Periodic partial
draining of these tanks from the bottom to eliminate sediment may control
legionellae proliferation.  This is especially important,  since environmental
microflora in the sediment are known to produce metabolites, possibly including
cysteine, which stimulate legionellae growth (Stout et al., 1985).  Removal
from other areas of the plumbing system where water stagnates may also prevent
or control legionellae growth (Stout et al., 1985).

Legionella                                                   March 31, 1987


Type of Water Fittings

     Information on the specific types of gaskets and fittings that support
the colonization of legionellae is not well documented.  One study of water
fittings as sources of L_. pneumophila in a hospital plumbing system was
carried out fay Colbourne et al. (1984a, 1984b).  In well-controlled experiments,
L^. pneumophila was isolated from rubber washers and gaskets, but not from
fiber or plastic fittings.  The ability of the bacteria to multiply when in
contact with the rubber fittings was demonstrated.  When the rubber fittings
were replaced with plastic fittings, L_. pneumophila could not be isolated up
to one year later.  The authors concluded that shower and tap fittings that
support growth of legionellae provide habitats protected from chlorine and
heat.  These foci may be seeded constantly or intermittently with legionellae
from hot water tanks or other amplifiers within the distribution system.

When to Control Legionellae in Plumbing Systems

     Legionellae are often found in the plumbing systems of hospitals which
have not experienced any cases of Legionnaires Disease.  One reason may be
that some strains are more virulent than others.  Currently, there is no
practical method for distinguishing the virulent strains from avirulent
strains.  For this reason, some experts feel that the mere presence of
legionellae in the absence of the disease is not sufficient grounds to under-
take control measures (Jakubowski et al., 1984).  They believe that health
care institutions should focus initially on surveillance for respiratory
illness, especially in high risk, patients, rather than to control legionellae,
in plumbing systems.  If nosocomial legionellosis is identified and environ-
mental strains match patient isolates, then control in plumbing systems is

     In contrast, Edelstein (1985) states that most authorities would probably
agree that disinfection of a contaminated site is indicated when:

     0  it is implicated as a source of an outbreak of Legionnaires Disease
        or Pontiac Fever;

     0  it is present in a hospital ward housing especially high-risk patients,
        such as an organ transplantation unit, regardless of epidemiological
        findings; in this case, selective decontamination of certain ward
        areas may be feasible; and when

     0  it is found in a building which has not been used for some time and
        in which the water has stagnated.

     Because of the virulence of some of these strains and the fact that at
least 25,000 cases/year or more occur in the U.S., a stronger preventive
approach could also be supported.

     In summary, there is no consensus on when measures should be undertaken
to control legionellae in the plumbing system of health care institutions.
Once virulence factors can be identified and virulent strains differentiated
from avirulent strains, routine monitoring of the plumbing system may become
more practical.

Legionella                                                   March 31, 1987

Until then, the Office of Drinking Water recommends that, on the basis of the
high incidence and mortality rate, health care institutions consider preventive
measures for the control of legionellae in their plumbing systems.  'These
measures could also control other opportunistic pathogens in the system which
might cause nosocomial infections.

     Legionellae are abundant in ambient water, and may survive water treat-
ment, especially since they are relatively resistant to chlorine.  Once in
the treated water, they then pass, probably at low levels, through the
distribution system.  It is also possible that legionellae enter the distri-
bution system through broken or corroded piping,  repair of existing mains,
installation of new mains, back siphonage, and cross connections.  When
legionellae enter hot water tanks, they settle to the bottom and, under
certain circumstances, will proliferate.  If they proliferate, plumbing
fixtures such as aerators, water fittings, and showerheads may be seeded,
resulting in colonization and growth at these sites.

     Inhalation of aerosolized potable water has been suggested from outbreak
investigations as a primary route of infection, although ingestion is also
a possibility.  The most susceptible individuals are those with underlying
diseases, especially those involving immunosuppression therapy.  In several
outbreaks, however, apparently healthy individuals have developed legionellosis.
Other risk factors include alcohol abuse, surgery and smoking.

     In order to reduce legionellae levels in drinking water, the presence of
organic matter and growth of algae and protozoa should be minimized in storage
reservoirs.  Moreover, newly-repaired or constructed components of the water
distribution system should be flushed thoroughly and disinfected before being
put into operation.  Even after flushing and disinfection, one cannot assume
legionellae have been controlled, since design factors in the distribution
system may impede the efficiency of these measures.

     In order to control legionellae growth in hot water plumbing, several
approaches may be considered.  Most of the published data have examined the
effectiveness of chlorine and/or heat.  The maintenance of free chlorine has
been found effective for controlling legionellae.  Shock chlorination also
is effective, but unless free chlorine is maintained within a system, the
organism may reappear.  Control probably can be achieved if free chlorine
levels in the hot water are maintained at 8 mg/L, but at this level corrosion
of pipes may occur.  In some cases, control may be achieved at 1.5-2 mg/L
free chlorine.  Undoubtedly, the level of chlorine found effective will
depend, in part, on the design criteria of the plumbing system.  A pertinent
facet in controlling legionellae is the difficulty of controlling batch
chlorination and of maintaining a chlorine residual in hot water.  This
problem can be minimized by using a continuous-flow proportional chlorinator
in the hot water system.

     Heat shock may eradicate legionellae in hot water tanks, if the temperature
at the bottom of the tank is maintained at 70C for one hour, but this is a
temporary measure which must be done routinely to be effective.  Maintenance

Legionella                                                   March 31, 1987

of hot water at 55C or higher apparently controls the organism, while lower
temperatures may not.  If legionellae are controlled by heat, care must be
taken to prevent scalding of persons using the water, especially in health
care institutions.

     Disinfection of a plumbing system by heat treatment or chlorine treatment
alone may not be as effective as a combination of the two.  For example,
growth of legionellae may theoretically be enhanced on the cold water side of
a hot-cold water mixing valve in a heat-treated plumbing system, a location
where chlorine may be effective.

     Effective disinfection of legionellae by ozone, ultraviolet radiation
or ethylene oxide has not been demonstrated by field tests.

     In addition to chemical and heat disinfection, other procedures may be
effective in controlling legionellae.  Hot water tanks should be designed
to give uniform temperatures throughout.  Hot or cold water tanks used
intermittently should be disconnected from the system, drained, flushed,
and disinfected before being reconnected.  Hot water tanks should be drained
regularly or at least bled to remove accumulated sludge that may serve as
a substrate for growth of legionellae and other microorganisms.  Taps and
showers in unused areas of health care facilities should at least be flushed
before patients are exposed to them.  Finally, faucet sieves and aerators,
and rubber washers and gaskets in the plumbing system should be used with
caution, especially in institutions housing physically compromised individuals
and where hot water is maintained at temperatures lower than 55C.

Legionella                                                   March 31,  1987


Antopol, S.C. and P.O. Ellner.  1979.  Susceptibility of Legionella pneumophila
     to ultraviolet radiation.  Appl. Environ. Microbiol.  38:347-348.

Arnow, P.M. and D. Weil.  1984.  Legionella pneumophila contamination of
     residential tap water.  In:  C. Thornsberry, A. Balows, J.C. Feeley and
     W. Jakubowski, eds. Legionella:  Proceedings of the 2nd international
     symposium, June 19-23, 1983; Atlanta, GA.  Washington, DC:  American
     Society for Microbiology; pp. 240-241.

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