Legionnaires’ disease is a serious lung infection that may sometimes be fatal. It is caused by the legionella bacterial species that normally reside in natural water bodies like lakes and rivers or are present in soil and mud.
These bacteria invade the water supply system and may multiply there to cause an outbreak of infections.
Prevention of Legionnaire’s disease involves regular cleaning and maintenance of water works. Some of the preventive measures are outlined here (1-5):
- Since the bacteria survives in warm contaminated water, the temperature of water in the system should be below 20ºC (68ºF) or above 60ºC (140ºF).
- Since legionella prefers water that is contaminated with rust, algae, sludge, amoebae, slime, bioﬁlm, lime scale, corrosion products or other organic matter and other bacteria, keeping it clean also helps.
- There should be no stagnation of water as legionella thrives in water that is stagnant for long.
- Those travelling abroad may often bring in the infection. Thus, if any symptoms are seen, medical help needs to be sought.
- Those who are at risk like smokers, elderly those with AIDS, cancers, chronic lung or kidney disease or diabetes need to avoid public water systems that could be contaminated like whirlpool spas, hot tubs etc. in hotels, resorts and cruise ships.
There is a Legionella surveillance that is active in Europe and in the United States.
These also keep tabs on outbreaks, travel associated legionella infections and deaths due to the disease.
Detection of outbreaks and detection of clusters help enforcing preventive measures.
Prevention of Legionnaires’ disease in water cooling systems
Water cooling systems have several aspects that are regulated by legionella infection prevention guidelines. These include commissioning, operating, maintaining, cleaning and regular procedures.
There needs to be regular inspections for microbial growth, leaks, algae, blockages or stagnations and splashing.
The design of the systems should be such so that they can be cleaned regularly.
Exhaust should be discharged away from where it can be exposed to the public. Water in all the systems must be rapidly moving and chemicals should be added, when needed, to limit the build-up of scaling, microbial growth etc.
Cooling towers should be operated and maintained with regular inspections at least monthly with applicable water treatment, regular microbiological monitoring and six monthly cleaning routines.
Cleaning should include the physical cleaning as well as disinfections.
Prevention of Legionnaires’ disease in air conditioning systems
Air conditioning systems similarly need to be efficient in designing, commissioning, operating, maintaining and cleaning.
There should be good facility for exhausts away from public exposure and easy and safe access for maintenance of the air filters.
The air filters should be designed such that they do not accumulate moisture. There should be provision for regular maintenance.
When not in use, evaporative coolers should be kept dry. Heat exchange coils should have corrosion-resistant components to prevent clogging and contamination.
Maintenance and cleaning routines
Similar maintenance and cleaning routines are essential for:
- hot and cold water systems
- evaporative condensers
- misting machines
- spray systems
- fire extinguishers etc.
Prevention of Legionnaires’ disease from respiratory therapy
Respiratory therapy equipment like nebulizers and ventilators may also be contaminated. These are used in patients with lung disease, most of whom have a weakened defence against infection.
Tap water used in these instruments can bring in the infections. Thus only sterile water should be used for these instruments.
In oxygen nebulizers disposable parts should be used. After each use the nebulizers should be emptied and washed with soap water if disposable parts are not used.
The parts should then be washed and dried in a dishwashing machine where the temperature of the hot water is over 70ºC. Weekly disinfection is important.
Use of biocides
These prevent contamination of water systems. Broad-spectrum biocides control algae and slime as well as other microorganisms. Simple example of a biocide is Chlorination.
Reducing exposure to soil and mud
Legionella longbeachae is common in the soil. Exposure to the disease may be prevented by reducing exposure to soil and mud while gardening. This can be achieved by wearing gloves and a mask when potting etc.
Persons should avoid breathing in droplets of water from dripping pot plants and when watering plants. They need to wash hands after handling soil especially before eating or drinking.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)
Last Updated: Jul 31, 2012