Legionella in HVAC Systems

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Don’t ‘Dampen Down’ the Threat of Legionella.

Since 2015 there has been almost a thousand confirmed cases of Legionella infection in England and Wales. Thankfully only a small number of these have resulted in fatality.

Due to its pneumonia like symptoms, such as; chills, fever, a cough, fatigue, headache and muscle aches, Legionnaire’s Disease has often been misdiagnosed. Unlike enteric organisms that are usually ingested and infect humans via the gastro-intestinal tract, Legionella spp is an organism which causes infection in the respiratory system. If untreated, Legionellosis can cause severe respiratory illness and eventually respiratory failure. Although antibiotics can control the effects of the disease, as many as 30% of people who contract Legionnaire’s die from it.

As a result of its critical nature, the analysis of Legionnaire’s disease in England and Wales is part of the national surveillance scheme. The objectives of the surveillance scheme, which is co-ordinated by Public Health England, is to detect and control outbreaks of Legionella in England and Wales. As well as implement improvement plans to prevent further cases.
Legionella in HVAC
As the majority of us know, Legionella spp is linked to water and water supply systems, and the bacterium likes to multiply in standing warm water or moisture. Legionella spp is commonly associated with schools and hospitals, and other areas of high moisture potential and areas where heavy demands are placed on the heating and cooling systems, such as hotels, leisure centres and gyms. However, with ventilation, extraction and air conditioning systems being central to a food factory, there are many locations within a food manufacturing or processing facility where there is considerable potential for the proliferation of Legionella in HVAC systems.

Legionella in HVAC Systems

Although most commercial heating, ventilation & air conditioning (HVAC) systems do not use a direct water supply, it is possible for legionella spp to grow in the moisture that builds up in the systems. Most industrial HVAC systems operate at temperatures that are ideal for Legionella to grow. Therefore, HVAC systems should be designed in a way that allows for ease of cleaning and sanitation. They should also be constructed in a way that will effectively minimise moisture build up, the potential of Legionella growth and the spread of Legionnaire’s Disease.
Kitchen HACCP TR19
It isn’t just the moisture build up from extraction that is a potential breeding ground for legionellae. Organic contamination from kitchen exhausts and the fresh air intake could also pose a serious risk. The primary cause of air conditioning and Legionnaire’s Disease contamination is poor cleanliness, maintenance and design.

Minimising the risk of Legionella in HVAC Systems

It is important to ensure that HVAC fresh air intakes are located in a safe position that limits the potential exposure of legionella organisms, for example away from cooling towers, condensers and areas of still or stagnant water. Adequate barriers and maintenance procedures should also be implemented to limit the growth, transmission and exposure of Legionella bacteria.

Although Legionnaire’s Disease is not a food borne contaminant, nor is it contagious, it can be destructive to businesses, posing a negative financial threat from loss and reputational risk. It is the employer or person in control of a premises or systems in connection with where the risk is likely to present (engineers), who have Legionella management requirements that need to be complied with. The responsible person(s) need to take suitable precautions to prevent or control the risk of exposure to legionella, this includes Hazard Analysis and Critical Control Point (HACCP) plans.

HACCP Requirements for the control of Legionella

The principles of hazard analysis and control have been applied in many industries to prevent harm to individuals from recognised hazards. Since 1996, Hazard Analysis and Critical Control Point (HACCP) plans have been widely used to prevent disease from infectious organisms transmitted from food and water. If you’re involved in any aspect of a building’s HVAC system, then you need to be aware of the potential damage that Legionellae can cause, and your duty to control it under the Approved Code of Practice (ACoP) and HACCP requirements. This set of requirements stipulate that all the building water systems should be analysed at each point where water is processed. This includes where the water enters the building, the heating system and distribution piping and ventilation ductwork. Once this has been completed a HACCP plan can be put into place to prevent the growth and transmission of Legionellosis.
Legionella and mould
Regular maintenance and cleaning of any HVAC system is always recommended to improve indoor air quality and limit the potential for airborne contamination. This is particularly important for those in high risk areas such as food manufacturing facilities.

There are simple procedures that can be incorporated into these cleaning and maintenance schedules that will help to reduce the potential for legionella in HVAC systems:

  • Regular inspection
  • Good standard of maintenance and repair
  • High level of outside air supply rate
  • Replacing any water damaged areas
  • Ductwork cleaning & extractor cleaning
  • Air filter replacement
  • AHU maintenance
  • Air handling surveys & air quality monitoring


The food manufacturing industry have recommended HVDS for its products, services and advice. As a result we have become a ‘Trusted Partner in Clean Air’ to the Food Manufacturing industry. If you require more details about Legionella management in HVAC systems please contact us.


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