Legionella Glossary

 

Aerosol - A suspension in a gaseous medium of solid particles, liquid particles or solid and liquid particles having negligible falling velocity.

AFLP Amplified Fragment Length Polymorphisms- A highly sensitive method for detecting polymorphisms in DNA. Following restriction enzyme digestion of DNA, a subset of DNA fragments is selected for PCR amplification and visualisation.

Air-conditioning - A form of air treatment whereby temperature humidity and air cleanliness are all controlled within limits determined by the requirements of the air-conditioned enclosure.

Algae - A small, usually aquatic, plant which requires light to grow, often found on exposed areas of cooling towers.

Amoebae - Protozoa able to alter shape as a result of movements of cell processes. Protozoa generally live in fresh water, soil or as parasites in humans and animals. Some amoebae can ingest Legionella allowing them to replicate in a protected environment.

Antibodies - Substances in the blood which destroy or neutralise various toxins or components of bacteria known generally as antigens. The antibodies are formed as a result of the introduction into the body of the antigen to which they are antagonistic as in all infectious diseases.

Anti-Corrosive Chemicals - Also known as corrosion inhibitors. Chemicals which protect metals by: (a) passivating the metal by the promotion of a thin metal oxide film (anodic inhibitors); or (b) physically forming a thin barrier film by controlled deposition (cathodic inhibitors).

Anti-Stratification Pump - Another name for Shunt Pump (see below)

Artificial Water Systems - Any water system that has been constructed and does not occur naturally such as a hot water system.

Audits - See also Legionella audits. The inspection and verification of an existing Legionella risk management system. This would normally involve the review of existing Legionella risk assessment reports and other documentation to ensure all critical risks are addressed and action plans are operational.

Bacteria - (singular bacterium) a microscopic, unicellular (or more rarely multicellular) organism.

Biocides - A substance which kills micro-organisms.

Biodispersants - A chemical product that can be added to recirculating water within a cooling system to penetrate and break down biofilms.

Biofilm - A community of bacteria and other micro-organisms, embedded in a protective layer with entrained debris, attached to a surface.

Blow-Down/Bleed-Off - Water discharged from the system to control the concentration of salts or other impurities in the circulating water; usually expressed as a percentage of recirculating water flow.

Calorifier- An apparatus used for the transfer of heat to water in a vessel by indirect means, the source of heat being contained within a pipe or coil immersed in the water.

CFU or Colony Forming Units - A unit of measurement used in microbiology that indicates the number of microorganisms present in a water sample. It is normally measured by the number of colony forming units (CFU) present in one millilitre of water.

Chlorine - An element used in disinfection.

Cold Water Service (CWS)- Installation of plant, pipes and fitting in which cold water is stored, distributed and subsequently discharged.

Concentration Factor - Compares the level of dissolved solids in the cooling water with that dissolved in the make-up water (also known as cycle of concentration). Usually determined by comparison of either the chloride or magnesium hardness concentration.

Cooling Tower - An apparatus through which warm water is discharged against an air stream; in doing so part of the water is evaporated to saturate the air and this cools the water. The cooler water is usually pumped to a heat exchanger to be reheated and recycled through the tower.

Corrosion Inhibitors - Chemicals which protect metals by: (a) passivating the metal by the promotion of a thin metal oxide film (anodic inhibitors); or (b) physically forming a thin barrier film by controlled deposition (cathodic inhibitors). See anti-corrosion chemicals above Coliform

 

Dead End/Blind End- A length of pipe closed at one end through which no water passes.

Deadlegs - Pipes leading to a fitting through which water only passes when there is draw-off from the fitting.

Decontamination - The process of removing or neutralising pathogenic bacteria in a water or other system.

Dipslides - A dipslide is a means of testing the microbial content of liquids. It consists of a plastic carrier bearing a sterile culture medium which can be dipped in the liquid to be sampled.It is then incubated to allow microbial growth.The resulting microbial colonies are estimated by reference to a chart.

Disinfection - A process which destroys or irreversibly inactivates micro-organisms and reduces their number to a non-hazardous level.

Distribution Circuit- Pipework which distributes water from hot or cold water plant to one or more fittings/appliances.

Domestic Water Services - Hot and cold water intended for personal hygiene, culinary, drinking water or other domestic purposes.

Drift - Circulating water lost from the tower as liquid droplets entrained in the exhaust air stream; usually expressed as a percentage of circulating water flow but for more precise work it is parts of water per million by weight of air for a given liquid to gas ratio.

Drift Eliminator - More correctly referred to as drift reducers or minimisers - equipment containing a complex system of baffles designed to remove water droplets from cooling tower air passing through it.

Evaporative Condenser - A heat exchanger in which refrigerant is condensed by a combination of air movement and water sprays over its surface.

Evaporative cooling - A process by which a small portion of a circulating body of water is caused to evaporate thereby taking the required latent heat of vaporisation from the remainder of the water and cooling it.

Fill/Packing - That portion of a cooling tower which constitutes its primary heat transfer surface; sometimes called 'packing' or 'pack'.

Flushing - The process of draining and cleaning a cooling system, including all associated pipework.

Fouling - Organic growth or other deposits on heat transfer surfaces causing loss in efficiency.

Half-Life - Ratio of system volume to purge rate.

Hot Water Services (HWS) - Installation of plant, pipes and fittings in which water is heated, distributed and subsequently discharged (not including cold water feed tank or cistern).

Legionaires' Disease - A misspelling, more correctly spelt Legionnaires' disease which is a form of pneumonia caused by Legionella bacteria.

Legionella - Type of aerobic bacterium which is found predominantly in warm water environments. (singular of legionellae).

Legionella Audits - The inspection and verification of an existing Legionella risk management system. This would normally involve the review of existing Legionella risk assessment reports and other documentation to ensure all critical risks are addressed and action plans are operational

Legionella Bacteria - (singular bacterium) a microscopic, unicellular (or more rarely multicellular) organism. The germ which causes Legionnaires' disease is a bacterium called Legionella pneumophila.

Legionella Bacterium - (plural bacteria) a microscopic, unicellular (or more rarely multicellular) organism. The germ which causes Legionnaires' disease is a bacterium called Legionella pneumophila.

Legionella Bacterium - (plural bacteria) a microscopic, unicellular (or more rarely multicellular) organism. The germ which causes Legionnaires' disease is a bacterium called Legionella pneumophila.

Legionella Disease - A name sometimes used to describe Legionnaires' disease. Legionnaires' disease is a form of pneumonia caused by Legionella bacteria. Legionella is a type of aerobic bacterium which is found predominantly in warm water environments (singular of legionellae).

Legionellae - The genus legionella belongs to the family legionellaceae which has over 40 species. These are ubiquitous in the environment and found in a wide spectrum of natural and artificial collections of water.

Legionella Longbeachae - One of the causative organisms of Legionnaires' disease. Has also been associated with soil, potting compost, mulches, compost heaps and composted animal manures.Particularly common in Australia although cases have been reported in other countries including the USA and Japan.

Legionella Pneumonia - Legionnaires' disease is a type of pneumonia. It was named after an outbreak of severe pneumonia which affected a meeting of the American Legion in 1976. The germ which causes Legionnaires' disease is a bacterium called Legionella pneumophila.

Legionella Pneumophila - One of the causative organisms of Legionnaires' disease.

Legionella Pneumophilia - A misspelling, more correctly spelt Legionella pneumophila which is one of the causative organisms of Legionnaires' disease.

Legionella Micdadei - The second most commonly isolated member of the Legionella family. The bacterium can cause flu like symptoms and pneumonia, including Pittsburgh pneumonia.

Legionella Sampling - Any monitoring programme should include routine sampling and testing for the presence of bacteria, both general (aerobic) bacterial species and Legionella bacteria. Detection of Legionella bacteria requires specialist laboratory techniques, although routine monitoring for aerobic bacteria can be used as an indication of whether microbiological control is being achieved.

Legionella Species - Currently there are at least 46 species and 70 serogroups of Legionella

Legionellosis - Any illness caused by exposure to legionella.

Legionnaires' Disease - A form of pneumonia caused by Legionella bacteria.

Lochgoilhead fever - An illness similar to legionnaires' disease caused by a species of legionella called Legionella micdadei. Was so called after an outbreak in Lochgoilhead, Scotland The incubation can be up to 9 days. A high percentage of those exposed to this agent tend to be affected. There have been no recorded deaths associated with Lochgoilhead fevers.

Make-Up Water - Water which is added to a cooling water system to compensate for wastage (e.g. via system leaks), evaporative loss and bleed.

Micro-Organism - An organism of microscopic size including bacteria, fungi and viruses.

Multi-Locus Sequence Typing - A method of molecular typing, relying on DNA sequence analysis of nucleotide polymorphisms in several genes. This technique has shown a high degree of intra-species discriminatory power for bacterial and fungal pathogens.

Non-Oxidising Biocide - A non-oxidising biocide is one that functions by mechanisms other than oxidation, including interference with cell metabolism and structure.

Nutrients - A food source for micro-organisms.

Oxidizing Biocides - Agents capable of oxidizing organic matter, eg cell material, enzymes or proteins which are associated with microbiological populations resulting in death of the micro-organisms. The most commonly used oxidizing biocides are based on chlorine or bromine (halogens) which liberate hypochlorous or hypobromous acids on hydrolysis in water. The exception is chlorine dioxide, a gas which does not hydrolyse but which functions in the same way.

Parts Per Million (ppm) - a measure of dissolved substances given as the number of parts there are in a million parts of solvent. It is numerically equivalent to milligrams per litre mg/l with respect to water.

Pasteurisation - Heat treatment to destroy micro-organism usually at high temperature.

PCR - Polymerase chain reaction.

Phenotypic Variations - Differences in the expression of genes as determined by observable characteristics such as the presence or absence of a particular cell component.

Planktonic - Free floating micro-organisms in an aquatic system.

Plume - The visible discharge of air and moisture from a cooling tower or other scooling system. This can include condensation and aerosols and as such represents a potential Legionella risk.

Pond/Sump - Collection of cooling water at the base of a cooling tower.

Pontiac Fever - A disease caused by species of legionella, an upper respiratory illness less severe than Legionnaires' disease. There have been no recorded deaths associated with Pontiac.

PPE - Personal Protective Equipment. Used to protect personnel during hazardous operations.

Retention Time - Time a chemical is retained in the system.

Risk Assessment - Identifying and assessing the risk from legionellosis from work activities and water sources on premises and determining any necessary precautionary measures.

Scale - Crystalline deposits that form on system surfaces or pipework. Scale normally results from a build up of unwanted minerals, usually calcium carbonate. See also scale inhibitors.

Scale Inhibitors - Chemicals used to control scale. They function by holding up the precipitation process and/or distorting the crystal shape, thus preventing the build-up of a hard adherent scale.Sediment

Sentinel Taps- For a hot water services - the first and last taps on a recirculating system. For cold water systems (or non-recirculating hot water systems), the nearest and furthest taps from the storage tank. The choice of sentinel taps may also include other taps which are considered to represent a particular risk.

Sero-Group - A sub-group of the main species. Serogroups are groups of microorganisms only differing by their composition in terms of antigens.

Sessile - Aquatic micro-organisms adhering to a surface normally as part of a biofilm.

Shunt Pump - A circulation pump fitted to hot water service/plant to overcome the temperature stratification of the stored water. Water should be circulated from the hot zone to the cool zone which is normally from the top to the base of the calorifier.

Slime - A mucus-like exudate which covers a surface produced by some micro-organisms.

Sludge - A general term for soft mud-like deposits found on heat transfer surfaces or other important sections of a cooling system. Also found at the base of calorifiers and cold water storage tanks.

Spa Pools - A spa pool is a self-contained body of warm water designed for sitting in (not whole body immersion). It is intended for a small number of people to use at one time.The water is re-circulated and kept between 30 - 40 oC and is usually not drained between use and is continually filtered and cleaned. A hydro-jet circulation, with or without an air induction bubble system, is also used to agitate the water. Spa pools are known under a range of names - spa bath, hot spa, hot tub, portable spa, whirlpool spa, swim spa and often Jacuzzi. All systems usually work in the same way.

Spray Drift - Aerosol emissions from cooling towers due to fan forced or extracted air exiting the cooling system or tower. This can include condensation and aerosols and as such represents a potential Legionella risk.

Stagnation - The condition where water ceases to flow and is therefore liable to microbiological growth.

Strainers - A coarse filter usually positioned upstream of a sensitive component such as a pump control valve or heat exchanger to protect it from debris.

Surfactants - Soluble surface acting additives that help to reduce the surface tension between water and particulate matter.

Thermal Disinfection - Heat treatment to disinfect a system. See also Pasteurisation.

Thermostatic Mixing Valves - Mixing valve in which the temperature at the outlet valve is pre-selected and controlled automatically by the valve. These should be of the automatic type where the hot water automatically shuts off if the cold water fails.

Total Viable Counts (TVC) - The total number of culturable bacteria (per volume or area) in a given sample (does not include legionella).

Windage - Physical loss of water from a cooling tower caused by draught of air or wind - water is lost around the base of the cooling tower as a result of cross winds as opposed to drift.

 

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