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In our previous blog about shelf life determination during the manufacture of a food product, Zarina Mohd, process project manager discussed the likelihood of a pathogen surviving the manufacturing process. In this blog, she will be covering the topic of pathogens called Legionella bacteria, which can be transmitted by aspiration during the manufacturing process, when liquids or food are accidentally inhaled into the lungs.

Legionella bacteria can cause Legionnaires’ Disease and a mild flu-like illness called Pontiac Fever. The disease is also known as Legionellosis and it is a form of a typical pneumonia caused by any type of Legionella bacteria. People can get the lung infection when they breathe in small droplets of water in the air that contains the bacteria. It is uncommon, but it can be very serious if contracted.

The bacteria are a persistent hazard in all water systems. A low count of Legionella bacteria is unlikely to cause harm, but the danger is when the bacteria quickly multiplies to harmful levels. The Ideal conditions for bacteria present in water ranges between 20°C and 45°C for long periods of time. But what does this mean for food manufacturers? It means that the distribution system for their water supplies must not provide opportunities for contamination or the multiplication of this microorganism as the results could be fatal.

There is a Legionella risk assessment which is a legal requirement in the UK. The first British Standard on assessing the risk of Legionella was published in 2010 and the food manufacturers now have to follow a code of practice to control the threat – using British Standard update BS 8550-1:2019. This update includes an annexe that applies to food manufacturing facilities that use pasteurisation equipment.

Pasteurisation is a critical control point for many food manufacturers; the process of heating to a specific temperature, to kill off or slow microbial growth in the food. However, the pasteurising process also has the potential to promote Legionella growth due to the various heat and cooling cycles that use water as the temperature source. Cooling systems should be designed and constructed so they comply with the current British Standard. Food manufacturers that operate these systems will require Legionella risk assessment and control programmes to be implemented due to the pasteuriser’s usage or storage of water which can potentially create spray or aerosol.

It is important to introduce measures to reduce the risk of exposure to Legionella bacteria by keeping the water system clean and free from unwanted nutrients and bacteria. The Legionella bacteria multiply where nutrients are available, including iron from corrosion and water contaminants that can trap nutrients, affecting the hardness scale. When referring to the contamination, prevention is always preferable to treatment!

In our previous blog, we discussed how to put a stop to bacterial biofilms due to the fact that foodborne pathogens are known to be associated with the formation of biofilm in food processing environments – Legionella outbreaks are linked to the existence of biofilms.

The temperature is a key factor for the establishment of a biofilm colony of Legionella. Ensuring incoming and stored water remains at a temperature of less than 20°C, and used water is heated above 55°C, will reduce the amount of the bacteria in water systems. Daily pasteurising at a minimum period of one hour at 60°C can ensure the elimination of any Legionella bacteria.

However, a water system can include plant, equipment and components connected with the system including associated pipework with dead-legs or parts that are only used intermittently. Stagnant water favours Legionella growth, which creates a risk of microbial growth going unnoticed and causing dangerous contamination if let back into the water system. Keeping pipe work as short and direct as possible with adequate insulation for pipes and tanks can help to prevent the risk. The best way for prevention is by simply monitoring the water system for usage and carrying out regular flushes to keep water flowing through the pipework, preventing stagnation.

There are many factors that can be attributed to the development of harmful bacteria in a water system within a food factory facility. All systems require a suitable and sufficient risk assessment, as a whole and not in isolation, to identify and assess the risk and any precautionary measures needed to prevent or control any revelation to Legionella bacteria. This should include an up-to-date schematic diagram showing the layout of the plant or system, including parts which are temporary out of use. Once the risk has been identified and assessed, a written scheme should be prepared for preventing and controlling it.

The risk from exposure should normally be controlled by measures which do not allow the growth of Legionella bacteria in the system. Where this is not practical, the risk may be controlled by minimising the release of water droplets and aerosols that can prevent the spread of this deadly bacteria.


Integrated Food Projects have partnered with Kettleby Foods on a number of high-profile multi-million pound capital projects since 2003/4, helping the business to develop and grow. Throughout that time they have provided cost-effective and efficient solutions on development projects both at our existing ready meals production facility and also in creating a new satellite facility. The projects at our existing facility were managed without impact on our ability to service our own clients, and all projects have been delivered within budget, in a timely fashion and to the requisite standards of safety and quality. Their team work ethos and professional approach ensure successful projects and I would utilise Integrated Food Projects in the future without hesitation.

- Jarrod Thorndyke, Production Director

I have worked with Integrated Food Projects on many capital expenditure projects since 2004, the latest being the development of the new plot of land adjacent to our main site. They successfully employed a project delivery process to ensure the integration of a leased modular building solution with the development of the site infrastructure to improve logistics and Health and Safety. Their staff are always positive and enthusiastic and have fostered a team-work approach ensuring another successful project delivered. I look forward to working with them again in the near future.

- Engineering Manager, Major UK Ready Meals Manufacturer