Legionella - Two Birds with One Stone
In 2018 there was a lot of information about Listeriosis, the disease caused by the deadly Listeria monocytogenes. But this is not the only “L” word you should know about in the food industry. While we have been heavily focused on the consumers of our products, we also need to protect our employees. Fortunately, the controls you should have in place for your food safety management system can also assist in minimizing the potential for Legionella too.
Legionellosis - another “L” word
Legionellosis, or disease caused by bacteria from the genus Legionella should feature in this regard. In this case, contaminated water is the vehicle and infection is acquired from inhalation of contaminated aerosols.
Although the majority of Legionnaires’ disease cases are isolated and sporadic, outbreaks have been known to occur commonly associated with buildings or structures that have complex water systems, such as hotels, hospitals and cruise ships. The most likely sources of infection include water used for drinking and showering and air-conditioning cooling towers.
Location, location, location
The Listeriosis outbreak highlighted the need to identify and actively manage the potential growth factors or areas in your facility to ensure the pathogen does not become a problem in your product. This is the lesson we should extend to managing Legionella.
Ideal growth factors
The ideal growth factors that can cause a problem are:
- Water stored at the correct temperature for growth (20oC to 45oC)
- Standing water such as water storage tanks
- The potential for aerosolization, for example during cleaning
Most of these factors can be found in a food facility due to the use of cooling systems, water used for cleaning and even the use of borehole water. Disruptions in water supply can also increase the probability of contamination – this is a very real concern in some local municipalities and in drought-stricken areas.
High risk areas in your facility
The following are considered high risk areas in food facilities for possible contamination by Legionella:
- Hot and cold-water plumbing systems
- Cooling towers
- Evaporative condensers often found in air-conditioning systems
- Water fountains
- Fire sprinkler systems
- Water-cooled machine tools
- Hot water jackets for tanks
These areas should be included on your sampling schedules for regular testing to ensure your employees and contractors are not exposed to this hazard.
Chlorination not a cure
Water stored in a food facility is often chlorinated to prevent the growth of micro-organisms. However, this does not control Legionella as Legionella pneumophila is a facultative intracellular bacterium that can invade human macrophages and can also replicate inside amoebae. These amoebae, if present in the stored water, can serve as a reservoir for L. pneumophila, as well as provide protection from environmental stresses, such as chlorination.
Contracting the disease(s)
Although Legionella bacteria are ubiquitous in the environment, they rarely cause disease. A combination of factors is required for the disease to develop:
- presence of a virulent strain in a water source
- means for dissemination (aerosolisation) of the bacteria,
- environmental conditions allowing the survival and inhalation of an infectious dose of the bacteria,
- a susceptible host, someone with a suppressed immune system would be ideal including employees ≥50 years, male gender with chronic underlying disease including diabetes and heart or lung disease, HIV and TB, high alcohol intake, current or past history of heavy smoking, immunosuppression / immune system disorders such as organ transplant recipients or persons receiving chemotherapy are high risk individuals. Chances are some of these are working at your facility.
Legionnaires’ disease is usually acquired through the respiratory system by the inhalation of air droplets that contain Legionella bacteria. After inhalation, symptoms usually commence within 2 to 10 days, but may commence up to 3 weeks after exposure. Legionnaires’ disease is a relatively uncommon form of pneumonia, which has a high case-fatality rate of 10-15% (up to 30%). Symptoms include flu-like illness (high fever, muscle aches, headaches), followed by a dry cough and progression to pneumonia.
Approximately 20-50% of people with LD may also present with diarrhea, and approximately 50% may show signs of mental confusion. If not treated, the symptoms normally worsen rapidly and may result in respiratory failure, shock, multi-organ failure and death.
Pontiac fever is a non-pneumonic illness also caused by Legionella bacteria. It has a shorter incubation period of 12-48 hours, presents as a mild flu-like illness, and lasts up to a few days. The illness is self-limiting, and no antibiotic treatment is necessary for this illness. So, you and I may have had it and not even realized!
Diagnosis and treatment
The most commonly used diagnostic test is the detection of Legionella antigen in a urine specimen during the acute phase of illness. The preferred diagnostic method is culture from a respiratory specimen such as sputum, which enables strain characterisation and this allows for comparison of strains from environmental and clinical sources.
The good news is that just like Listeriosis, if there is early diagnosis, effective antibiotic treatment is available.
How to prevent a Legionella problem in your facility?
The proper design, maintenance and temperature of potable water systems are the most important method for preventing the growth of Legionella.
- Hot water should be stored above 60?C and delivered to taps above 50?C. Rather install as mixer on the taps to ensure water is at the correct temperature when used than store it too cold.
- Cold water should be stored below 20?C, and dead legs or low flow areas must be eliminated.
Although water testing results may yield a negative result from a sample, this should not lead to a false sense of security as any system with suitable conditions can quickly become colonised. Testing is not a substitute for sound maintenance and effective water treatment programme – you should manage this as part of your PRP.
There are currently no vaccines available for the prevention of Legionnaires’ disease, and prior infection does not necessarily prevent reinfection.
Note: Legionnaires’ disease is a notifiable condition in South Africa.
For specific guidance, you should consult:
SANS 893:2013 which consists of the following parts, under the general title Legionnaires’ disease:
Part 1: Risk management.
Part 2: The control of Legionella in water systems.
© Macleans Chimwenye, QPRO SAI Global via Food Focus