-
Confirm the diagnosis
-
Identify potential sources of infection
-
Report the case to the appropriate
MOH who in turn reports to HPSC
-
Search for links with other cases
-
Investigate possible sources of
infection.
Confirm the diagnosis For the purposes of surveillance
and public health action, the clinical diagnosis of
Legionnaires disease should be supported by confirmed
or probable microbiological evidence of recent Legionella
infection (see Chapter 1, Section 1.7). When the clinical
and microbiological evidence is consistent with a
diagnosis of Legionnaires disease both the attending
physician and director of the microbiology laboratory
should notify details immediately to the relevant
department of public health (MOH). The department
of public health should then liaise with the environmental
health department and other relevant agencies to ensure
timely, appropriate and thorough investigation. Identify
potential sources of infection
For each confirmed or probable case of Legionnaires
disease, the patients movements during the incubation
period should be recorded. It is essential to detail
the patients movement accurately to facilitate identification
of possible sources of infection. Although the incubation
period in Legionnaires disease is between two to ten
days, given that the exact onset of an illness is
not always certain, enquiries should be made for the
two weeks before the onset of illness.
Patient risk factors for Legionnaires disease e.g.
immunosupression treatment, diseases associated with
impaired immune response should be specifically enquired
about and recorded.
Details of the patients movement in
the two week period prior to the onset of illness including
full address of places of residence/over night stays,
places of work, places of leisure and travel details
should be obtained. Exposure to any recognised potential
environmental sources of Legionella should also be specifically
asked about and recorded including:
-
Water systems incorporating a cooling
tower
-
Water systems incorporating an evaporative
condenser
-
Hot and cold water systems
-
Spa pools
-
Natural thermal springs and their
distribution systems
-
Respiratory and other therapy equipment
-
Humidifiers
-
Dental chair unit waterlines
-
Fountains/sprinklers
-
Water cooled machine tools
-
Vehicle washes
-
Potting compost/soil in warmer climates
Other plants and systems containing water which is
likely to exceed 200C and which may release a spray
or aerosol (i.e. a spray of droplets and/or droplet
nuclei) during operation or when being maintained.
A diary (Checklist 5) of every place the patient
has visited for the two weeks prior to onset of illness
should be filled out by the patient (or surrogate
if too ill). The list of potential environmental sources
and locations in Checklist 6 can be used to maximise
the likelihood of identifying possible risk sources
Report the case
On receipt of the notification the MOH should report
the case to HPSC using the specific Legionnaires
disease surveillance form (Appendix J) or CIDR where
relevant. Even where details are incomplete, cases
should be reported. The completed details should be
provided as they become available. Where travel-associated,
HPSC will inform EWGLINET as appropriate.
Where a place of work is a potential source of infection
for a case, this should be brought to the attention
of the HSA as a matter of priority by the department
of public health/MOH in the relevant area
Search for link with other cases
The MOH and HPSC will check for links with other
cases based on infectious disease notifications to
the area, HPSC, local hospitals, neighbouring HSE
areas or EWGLINET for linked cases in other countries.
Investigate possible sources of infection
The key to the investigation of Legionnaires disease
is in the detailed enquiry of the cases exposure to
potential environmental sources of Legionella in the
two weeks prior to the onset of symptoms.
8.2.1 Community-acquired case - single case
Legionella are widespread in the environment. Aerosols
containing the organism can be dispersed into the
atmosphere and travel distances of up to 500 metres
from their source.145 If the patient has a history
of exposure to a recognised potential source of Legionella
infection outside of hospital or a domestic premises,
examination of the maintenance records of these systems
including water systems should be requested by the
department of public health in consultation with the
environmental health officer, consultant microbiologist
and where relevant, other agencies such as the HSA.
With the diagnosis of a confirmed/probable case sampling
of potential environmental sources to which the patient
was exposed should be carried out based on a risk
assessment. Pending results of the sampling, and subsequently
when sample results are available, steps may need
to be taken to prevent risk to others and to identify
other cases - possibly undiagnosed.
For all locations where water is the potential source,
the water system risk assessment should be reviewed,
maintenance records checked and a search made for
other cases. Any deficiencies identified by the risk
assessment should be remedied as soon as possible.
Interim measures may need to be put in place until
these remedial measures are fully in place. If precautionary
disinfection of parts of the water systems is considered
necessary this should only be undertaken after taking
relevant samples. The latter should be done as a matter
of urgency.
In addition, if the patients place of work is a potential
source of infection, the co-operation of management
or the relevant occupational health department, if
appropriate, should be sought to identify recent levels
of sick leave or respiratory symptoms among the workforce
to identify other potential cases.
If the patient lives in a nursing home/residential
home/institutional setting, the water systems should
be assessed as above. As part of the search to identify
other cases, checks should be made about unexplained
respiratory symptoms among other residents, current
and past. The time period to review should be informed
by the likely duration of any identified potential
source of infection including water system deficiency.
Water under pressure as found in spa pools, fountains,
sprinklers, etc. is a recognised source of Legionnaires
disease. Large outbreaks have been associated with
pools on display as well as in use.146 If a patient
reports exposure to such sources, as part of the control
measures the maintenance requirements and records
for that source should be reviewed to ensure they
comply with published guidelines e.g. those for spa
pools
Internationally, potting compost is a recognised
source of L. longbeachae and has been associated with
cases of Legionnaires disease, particularly in Australia.
Domestic premises A proportion of sporadic cases
of Legionnaires disease may be residentially acquired.147
This is more likely to occur if a patient uses for
example a shower after it has been out of use for
some time e.g. a week or more. Testing for Legionella
in domestic water systems can be crucial, as can molecular
typing, when more than one environmental source is
identified.
8.2.2 Travel-associated cases
A case is defined as travel-associated if the patient
spent one or more nights away from home, in the ten
days prior to the onset of symptoms, in accommodation
used for commercial or leisure purposes e.g. hotels,
holiday apartments, ships, campsites, etc. Where such
stays were abroad, HPSC should forward the details
to EWGLINET to facilitate the identification of clusters
and risk locations.
Where the travel or leisure premises is in Ireland,
arrangements should be made to sample potential environmental
sources. At a minimum, arrangements should be made
to assess the premises, inspect maintenance records,
sample as indicated and initiate/recommend protective
measures. The relevant department of public health
should ensure that the accommodation site receives
the checklist from the EWGLI guidelines on travel-associated
Legionnaires disease that outlines good practice
for minimising the risk of Legionella infection (Appendix
H).
Legionnaires disease can occur up to ten days after
the patient returns to their own home. Exposure could
be linked to this domestic source rather than the
leisure/commercial accommodation. A travel history
is not sufficient to imply causation. Isolation of
Legionella from the patients home of the same type
as that isolated from the patient suggests infection
at home rather than travel related.
8.2.3 Nosocomial infection
Investigation is essential for every case of nosocomial
Legionnaires disease. This is particularly urgent,
given the vulnerability of other patients, where it
cannot be excluded as having been acquired in hospital
(see definitions Chapter 1, Section 1.7).
When a confirmed or probable case of nosocomial Legionnaires
disease is identified an investigation team should
convene with the relevant consultant microbiologist
as chair, or if relevant a CPHM. The team should consist
of infection control personnel from the hospital,
at least one senior physician, senior hospital engineer,
senior hospital management representative, a CPHM,
PEHO and others as appropriate e.g. occupational health
staff.
The team should identify and address investigation,
control and prevention measures.
The risk assessment for control of Legionella in
water systems, including water supplies for general
use and display, water therapies and respiratory therapy
equipment, and maintenance records should be reviewed.
Samples should be taken.
Potential environmental sources are listed in Chapter
1, Section 1.3. Of particular relevance in the hospital
setting are the hot and cold water distribution system,
wet spray cooling water systems, showers or spray
washing equipment, drainage systems and taps, spa
pools, whirl pool baths or therapy pools, respiratory
therapy equipment, clinical humidifiers, humidifiers
in ventilation systems, cooling coils in air conditioning
systems, fountains, ornamental water features and
sprinklers.
Any deficiencies identified by the risk assessment
should be remedied as soon as possible. Interim measures
may need to be put in place to protect patients until
these remedial measures are in place. If precautionary
disinfection of parts of the water systems is considered
justified, this must only be undertaken after any
sampling. This latter should be done as a matter of
urgency.
Simultaneous to the risk assessment an active case
search should be conducted for other nosocomial cases
including unexplained pneumonia and respiratory illness
among patients or hospital staff. The GPs of in-patients
discharged from the suspect units/wards/institution
should be contacted to enquire about patients attendance
with pneumonia and respiratory illness since hospital
discharge. Similarly, for those transferred to other
institutions. Occupational health staff should review
records of staff absence due to respiratory illness.
The investigation team will determine the time period
for inclusion.
As with travel-associated and community-acquired
case, where the patient did not spend all of the incubation
period in the hospital other possible sources of infection
must also be investigated. As mentioned earlier in
the chapter where more than one environmental source
is identified it is important to the investigation
that all sources are identified and tested so as to
inform control, remedial and preventive actions.
8.2.4 Summary
The investigation of single cases of Legionnaires
disease should always be carried out in a systematic
and methodical way (Figure 9). Single cases may be
the first reported case in an outbreak or may be truly
sporadic. Examination of the potential environmental
sources of infection for these single cases can highlight
problems that might otherwise remain undetected and
possibly contribute to the occurrences of further
cases.
8.3 Investigating an outbreak of Legionnaires disease
An outbreak can be defined as two or more cases of
Legionnaires disease associated with the same geographical
location or probable source during the preceding six
months. An outline of the outbreak investigation procedure
is shown in Figure 10.
A multidisciplinary outbreak management team (OMT)
should be convened by the relevant director of public
health. The team should include representatives from
the following groups:
-
Microbiologist
-
Physician
-
PEHO
-
CPHM
-
Representative of senior management
where appropriate
-
Infection control nurse where appropriate
-
HPSC where appropriate
-
Internal health and safety personnel
where appropriate
-
Engineer where appropriate
-
Press officer where appropriate
-
Occupational health where appropriate
-
And other personnel considered appropriate.
As for any outbreak advance arrangements should be
in place for:
-
Contact numbers of all OMT personnel
(and designates)
-
Logistical backup - clerical/administrative,
communications, headquarters etc.
-
Sampling equipment
-
Meteorological data acquisition
-
On-call provision for staff
-
Appropriate laboratory facilities
should be available
-
Liaison with other authorities -
local authorities, HSA, etc.
-
Liaison with GPs, hospital clinicians,
adjacent HSE areas if appropriate
8.3.1 Epidemiological investigation
The CPHM should ensure that the appropriate epidemiological
investigations are carried out which will include interviewing
cases (or their proxies), case finding (active and passive)
and appropriate epidemiological studies.
When a potential source(s) is identified in particular
settings, the check for additional cases by the CPHM
will include interviews with relevant management and
staff about recent illness history and staff absenteeism.
When the potential source is in a geographical location
rather than setting, the CPHM will use a multiple of
sources e.g. GPs, A&E etc in the search for additional
cases.
8.3.2 Microbiological investigation
Clinical samples for microbiological confirmation of
infection in suspected cases should be obtained, likewise
for environmental samples. Sampling should be carried
out by a competent person and microbiological analysis,
should preferably be carried out by a laboratory that
is accredited for the detection of Legionella species
from clinical and environmental samples and capable
of recognition of Legionella species and serogroups.
A microbiologist experienced in the microbiology of,
detection of, and ecology of Legionella species should
interpret the clinical and environmental laboratory
findings.
8.3.3 Environmental investigation
The PEHO or accredited commercial company should ensure
that the appropriate environmental investigations are
carried out including identification of potential sites,
early visiting of any identified implicated site and
sampling as appropriate.
8.3.4 Public relations
Arrangements should be made by the press officer to
keep members of the press informed as appropriate. The
OMT should agree press releases.
8.3.5 Overview of the activities of the OMT
The OMT has responsibility for overseeing the investigation
of potential sources of infection, including site surveys
and environmental sampling, emergency control measures,
recommending long term control measures and ensuring
a system for post-outbreak routine monitoring.
8.3.6 Investigation of sources
The initial aim in any outbreak investigation must
be to identify quickly the potential sources, to sample
them and then render them safe either by precautionary
disinfection and cleaning or by disabling the equipment
until it has been shown to be safe.
All relevant information should be passed to the OMT
as soon as possible and continuous contact should be
maintained between investigating personnel and the OMT
during the outbreak.
All potential sites of infection should be identified.
Pending identification of potential sources, environmental
health officers should carry out a door-to-door survey
of non-domestic property (likely to have "high-risk"
plant) in the suspect areas to ensure against the possibility
of "high-risk" plant being in operation without
the knowledge of the OMT. A survey of local cooling
towers should be carried out. High-risk plants should
be visited, inspected visually and water samples obtained.
Owners or occupiers having responsibility for the plant
should be requested to provide relevant documentation
and take appropriate steps to ensure that their plant
is not likely to be a source of legionnaires' disease.
An early visit to any implicated site(s) is essential.
The investigation should include the engineering, microbiological
and environmental aspects of implicated sources.
8.3.7 Site survey
This should consist of an analysis of the operational,
structural and facility elements. Survey of the design
and maintenance of any water system must be detailed
enough to enable valid decisions to be made about the
risk to health and control measures to be taken. It
should identify sources of Legionella on the premises,
points of entry of Legionella and any necessary precautionary
measures. The site is first examined to establish all
systems using water i.e.
- Systems which contain water at temperatures likely
to support the growth of Legionella
- Areas where growth of Legionella may be expected
to be greatest
- Cross contamination between free-flowing and stagnant
water
- Locations at which the potentially contaminated
water can be aerosolised
- Locations where the aerosol might be released into
the environment.
It should be noted that temperatures and disinfection
particularly influence the ecology of the water supply.
The possibility of alternative sources of Legionella
should also be kept in mind.
The route of the water should be followed from its
entry into the site to the point where it is used or
discharged. If a plan of the system does not exist or
is out-of-date one should be prepared showing the locations
of:
- The incoming water supply (mains or private source)
- All tanks/cisterns, expansion/pressure vessels,
booster vessels and pumps
- Any water softeners, filters or other treatments
- Any calorifiers/water heaters
The type and nature of materials and fittings (e.g.
taps, showers, water closet cisterns, pressure release
valves, and pipework) and the kinds of metals, plastics,
jointing compounds etc. present
- Cooling towers or heating circuits
- Air conditioning systems or humidifiers within the
building which are supplied with, and store, water
and which may produce aerosols
- Any other equipment that contains water and could
be a potential risk such as spa pools, humidified
display cabinets, machine tools, fountains etc.
The adequacy of management control systems and site
documentation including written procedures should be
assessed. Inspection and maintenance protocols, and
plant shut-down and start-up procedures should be examined.
Any examination of logbooks of the factory/hotel/hospital
water maintenance programme or other maintenance/operation
records should include:
- Dates and times of equipment changes
- Dates and times of changes in water sources
- Dates and times of significant changes in routine
(intensification in cooling tower use should have
been matched by increased disinfection)
- Sudden water pressure drops
- Disinfection and dosing history (any water treatment
company contacted and questioned).
- Interviews of management and staff actually involved
in maintenance, etc. and taking of statements on:
- Role and function
- Rosters
- Recent illness history
- Staff absenteeism
- Training
8.4 Emergency control measures
In addition to the normal operating procedures for
Legionella control, there should be a written emergency
action plan which identifies responsibilities, contact
details, materials to be available, and control measures
to be undertaken. This may include identification of
persons possibly having been exposed or having visited
the risk areas and communication with and notification
of relevant parties.
The emergency control measures should be implemented
as soon as possible after the outbreak has been recognised.
It should include the collection of appropriate samples
from pre-selected sampling points before any other actions
affecting the water distribution system are undertaken.
The next priority is the exclusion of persons from areas
of risk (identified by prior risk assessment) and the
closure of high-risk items (showers, cooling towers,
humidifiers or other as appropriate to the case). Non-essential
equipment such as spa pools, fountains and other ornamental
features should be shut down until remedial measures
are implemented.
Any risk assessment prepared earlier should be reviewed
or if none exists, should be undertaken at this stage.
This should identify any further emergency control measures
to be implemented. The exact choice of measures will
depend on the risk assessment and any available epidemiological
evidence. The measures will usually involve disinfection
of potential sources by high levels of chlorine, chlorine
dioxide or other effective oxidising biocides with biofilm-penetrating
and anti-protozoan properties, flushing out the distribution
system, cleaning of tanks, water heaters, water softeners,
etc. and raising the circulating hot water temperature,
if this is below 60C.
8.4.1 Thermal disinfection
Hot water systems
Thermal shock treatment for relatively short periods
of time has been used effectively as an emergency disinfection
procedure for hot water systems that can be implemented
quickly without the requirement for particular equipment.
Thermal disinfection is carried out by raising the temperature
of the water in the calorifier (hot water storage heater)
sufficiently (70-80C) so that water at each outlet does
not fall below 65C (this should be measured) and circulating
this water throughout the system. Each outlet should
be flushed sequentially for a minimum of five minutes
at 65C or above. The optimal flush time is unknown and
may depend on the characteristics of individual water
systems and longer flush times may be necessary. Thus
the process may be repeated on successive occasions.
Appropriate safety procedures should be employed to
avoid scalding and generation of aerosols.
It is important to emphasize that for effective thermal
disinfection:
The water system must be well insulated
The entire system must be exposed to a temperature
of 65C for at least five minutes
Dead legs or unflushed spurs will cause recontamination
and will necessitate repeat of the thermal treatment
at intervals
The procedure requires sufficient heat capacity in
the system and requires considerable energy and manpower
resources and is not usually practical for large buildings
but may be suitable for smaller systems
Thermal disinfection will not disinfect downstream
of thermostatic mixer valves and so is of limited value
where such valves are installed. Where thermostatic
mixer valves are installed to reduce scalding risks,
they must be subjected to a programme of planned maintenance
and monitoring.
Following heat shock treatment, tanks and calorifiers
should be drained and should be subject to physical
cleaning and descaling if necessary. Following cleaning,
the water system should be disinfected with high levels
of free available chlorine (20-50 mg/litre) or other
oxidising biocide. It is important to note that the
bactericidal action of free available chlorine is pH
sensitive and decreases rapidly at pH values > 7.
Thus the pH of the water in the system being treated
should be monitored and may need adjustment. At the
end of the procedure, samples of water and sediment
should be collected at distal outlets of the water system
and examined for the presence and density of Legionella
bacteria. If the result is unsatisfactory, the procedure
must be repeated until documented decontamination is
achieved. Following decontamination, microbiological
checks must be repeated periodically.
8.4.2 Chemical disinfection
Cold water systems
Emergency control measures for cold water systems include
disinfection of tanks and pipe work with high levels
of free available chlorine (10-50mg/litre) or other
oxidising biocide. This may not be effective if significant
amounts of sludge, scale and sediment are present in
the system and these may have to be removed by effective
cleaning before effective disinfection can be achieved.
Chemical disinfection requires a good working knowledge
of both the chemicals performance characteristics and
that of biofilms. For example, chemical disinfection
may corrode or damage sensitive equipment attached to
the water system e.g. reverse osmosis units; it may
not be effective at high temperatures in the hot water
system or it may lack biofilm penetration capability.
All disinfection is more effective if performed in conjunction
with physical cleaning, usually prior to disinfection.
In this case, having disinfectant present during cleaning
is necessary to reduce the risk of exposure to disturbed
biofilm and legionellae. Areas requiring special attention
include the high water mark and ballcock assemblies
in storage tanks and water softeners or other similar
reservoirs.
Cooling towers
Hyperchlorination (>10 ppm) of cooling towers usually
requires three treatments plus mechanical cleaning.
Higher doses may cause oxidation problems. For distribution
systems, circulation of 5 ppm free chlorine for a minimum
of three hours is necessary to inactivate free legionellae
and the outer layers of biofilm in the system. This
will achieve a suitable temporary risk reduction in
the system.
The operating temperatures of most cooling towers fall
within the optimum range for the rapid proliferation
of legionellae, namely 20C to 45C. However, the risk
can be mitigated by ensuring that the water temperatures
of the water supplying these systems, including storage
tanks and pipe work, are maintained below 20C. Where
water is required to be held hot for Legionnella control,
all outlets should be clearly labelled very hot to avoid
accidents.
NOTE
It must be emphasised that these are only interim measures
to reduce risk and buy time during which long-term remedial
measures should be formulated and implemented. The selection
of the long-term remedial measures must be based on
a thorough risk assessment combined with any epidemiological
information available. Effective long-term control depends
on the rigorous adherence to the control measures. The
measures will probably be a combination of those described
elsewhere in this document. They are likely to require
engineering modifications to the existing water systems
as well as improvements in monitoring controls, management
and staff training.
8.5 Outbreak report
A detailed report on the investigation, its findings
and any recommendations should be completed and delivered
to relevant people/organisations.
8.6 Post-outbreak routine monitoring
When a source has been identified following an outbreak
there is a clear need for monitoring for Legionella
thereafter to confirm the long term effectiveness
of the control measures and for monitoring of temperatures,
colony counts (aerobic heterotrophs), water volumes,
and disinfection. Sampling frequency after an outbreak
should be site specific and based on the risk assessment
and remedial measures enacted. It may initially be
as high as weekly then can be gradually reduced to
monthly and then perhaps quarterly and so on. Experience
shows that buildings that have had a problem frequently
have a recurrence if there is a lapse in control measures.
Sampling for Legionella should back up other more
immediate measures of effectiveness such as the monitoring
of temperature or chlorine concentrations. There is
no guarantee that Legionella will be eradicated from
a water system. A temporary eradication or a reduction
in numbers may only be possible.
The selection of long-term remedial measures should
also be based on a thorough risk assessment combined
with any epidemiological information available. Such
measures may require engineering modifications to
the existing water systems as well as improvements
in monitoring controls, management and staff training.
Effective long-term control depends on the rigorous
adherence to such control measures. A proper programme
of planned maintenance and operational management
of all water systems must be instituted. This should
include routine checks to ensure work is done in accordance
with specifications and to a satisfactory standard.
Any programme should be reviewed routinely or when
significant changes to routines occur. Maintenance
and operational staff must be adequately trained to
understand and carry out their responsibilities.
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