1. What is Legionella (where does the bacteria come from)?

Legionella is a bacterium that occurs naturally in moist environments, colonizing artificial or natural reservoirs of fresh water and moist soils.

2. What is Legionnaires' disease or legionellosis?

It is an infection caused by the Legionella pneumophila bacterium, which is a serious form of pneumonia (lung infection). In 15-20% of the cases, the infection is statistically fatal.

3. What is Pontiac Fever?

It is a non-pulmonary infection like the flu, caused by the Legionella bacterium. The infection resolves quickly. Approximately 95% of the people exposed will develop this infection.

4. How is the infection transmitted?

The infection comes from the inhalation of an aerosol of contaminated water (microdroplets). Contamination sources are facilities that favor the multiplication of the bacterium and its dispersion in the environment through the formed mist.

5. Can it be contagious? 

No, not at all.

6. Who is most at risk?

Mainly those with a weak immune system (eg, elderly, immunosuppressed transplant, etc.). Smokers and alcoholics are also at higher risk.

7. Why is a cooling tower a favorable place  to the development of Legionella?

The temperature of the water in cooling towers is ideal for Legionella's growth. Moreover, the presence of nutrients (scaling, corrosion, organic matter) and shelter (mud, dirt and amoebae) is often available. Eventually, the water droplets can travel up to one mile from the airflow and be the source of infection over a wide area.

8. How come that one tower is infested and not the other? What are the contributing factors?

Corrosion, scaling and fouling and the presence of silt are aggravating factors, thus providing nutrients and ideal locations for the development of legionella bacteria. A  facility that allows stagnant water is another contributing factor.

9. Are some tower designs more succeptible for proliferation than others?

Theoretically no however, a tower with a basin that drains poorly or with stagnant areas can cause an accumulation of mud, which obviously amplifies the problem.

10. How do the bacteria travel from cooling towers to the affected people?

Driven by wind, water droplets can travel several kilometers and become the source of infection in a large area.

11. How does the bacteria make it to the cooling tower?

Usually by the potable water network.

12. Why does the treatment of drinking water not eliminate the bacteria?

Legionella bacteria is not particularly strong but the amoeba (larger microorganism) present in drinking water is highly resistant to the regular disinfection methods. The amoeba becomes a ''Trojan horse'' harboring the parasite bacteria.

13. Can a tower contaminate another tower by air?

There is a possibility of seeding as the water is sprayed and can reach another tower. However, the bacteria will only multiply to a critical level if the terrain is favorable in the seeded tower.

14.  Are there other systems that can infect people with this bacteria?

Decorative fountains, spas, humidifiers and air washers, dental equipment, foggers, domestic hot water (showerheads), metalworking equipment (cutting oils) etc. are all possible vectors of infection.

15. Does the addition of biocides to cooling towers ensures the absence of Legionella?

No, it does not guarantee the absence of the bacterium. It can withstand certain conditions and may also be protected by the environment (deposits, biofilm amoeba).

16. Is there any specific biocide for Legionella?

Halogens such as bromine, chlorine, chlorine dioxide, etc. are all effective with the proper dosage. Among the non-oxidizing biocides, many of which are tested for Legionella are isothiazolin, DBNPA, and glutaraldehyde. Again, we must respect the required dosages.

17. At what concentration does the presence of Legionella pneumophila become dangerous?

If the concentration is above 100 pneumophila bacteria per milliliter, it is shown that it can be dangerous to the health of people.

18. In Canada and Quebec, is there a maximum standard in terms of Legionella pneumophila population in water?

There are two levels of intervention:

Over 10.000 CFU/L ( colony forming units per liter of water), corrective measures must be made to the maintenance program.

At 1 000 000 CFU/L, an emergency disinfection must be carried out and the maintenance program must be corrected and re-certified.

19. Is the total bacteria analysis by culture on a stick an adequate Legionella control measurement?

No, There is no correlation between the total population of bacteria and the presence of Legionella pneumophila.

20. Is the ATP analysis an adequate Legionella control measurement?

No, there is no correlation between ATP and pathogenic bacteria in cooling towers.

21. When we speak of disinfecting cooling towers, what does it mean?

Disinfection normally consists of using an oxidizing biocide, a biodispersant and mechanical cleaning. The steps are usually:

  1. Disinfect with an oxidant
  2. Physically empty and clean the tower
  3. Repeat another disinfection
  4. Repeat another test 48 hours later

22. What are the best products for disinfection?

Bromine gel primarily (and other halogens). The biodispersants must be part of the application to remove biofilms.

23. Why is disinfecting with chlorine not as effective as bromine?

Bromine is a better disinfectant than chlorine in alkaline pH, which is typically maintained in cooling towers.

24.  Is it possible that, even after disinfection, there is still the presence of bacteria?

Yes. There may be areas that contain contaminated bacteria. We should also be wary about the presence of dead legs.

25. Can a customer be present during the disinfection of a tower?

Yes, he can be present when using the necessary security measures, which means that he must wear an appropriate mask and protective clothing.

26. How can we eliminate the risk associated with Legionella?

We cannot eliminate, but rather minimize it by utilising best practices.

27. How can we reduce the risk?

Risk management is based on good maintenance practices including a water treatment program and effective performance evaluation. A sampling and a quick and reliable detection program must be in place to enable an effective response in the event of contamination. These results can be obtained within 48 hours of collection with modern analytical technologies, such as DNA detection. 

28. Que comprennent les forfaits Magnus en minimisation du risque?

Packages include a range of services for the detection and prevention of legionella through:

  • Water analysis by culture;
  • Monitoring the levels of legionella in water by DNA analysis;
  • Monitoring the levels of legionella in biofilm by DNA analysis;
  • Inspections and audits of optimization systems;
  • Implementation of preventive maintenance programs on chemical equipment and mechanical treatment;
  • Disinfection during start up;
  • Monitoring of microbiological indicators.

29. Are there any guides explaining good practices? Who publishes these guides?

Explanatory guides are published by the Quebec Building Authority (RBQ), ASHRAE, CTI, AWT, etc.. AWT provides guidelines on bacterial populations, so it is a more complete reference. Some European guides are also very detailed: HSE (Health & Safety Exectuvie), Approved Code of Practice and guidance, (ACOP 18, UK) et (EWGLINET) European Surveillance Scheme for Travel Associated Legionnaires’ Disease and (EWGLI) European Working Group for Legionella Infections.

30. Is there any legislation on this subject anywhere else (other countries)?

The City of Hamilton, Ontario, has an obligation to maintain a register which records everything. Several European countries and Australia have a legislation in place.

31. What are the analytical techniques available for Legionella pneumophila?

Method by culture analysis and by DNA analysis.

32. What is the difference between DNA detection and culture detection?

DNA detection is based on the detection and quantification of the bacterium's DNA. This technique allows for a quick and accurate measurement of the bacterial population (less than 48 hours), while it takes about 14 days to get the results of detection by culture. This method is more specific and identifies the complete profile of the bacteria, but it only detects culturable bacteria.

33. Is it really possible to identify the responsible tower of an infection?

Yes, if we compare the complete profiles of the collected bacteria from patients with those  in the cooling tower.

34. The results obtained by DNA detection are expressed in UG, what is it?

Genomic Unit.

35. Does the PCR unit corresponds to the UFC unit?

Statistically, there is no direct correspondence. It is similar but not equal.

36. Some offer a site test with immediate results, is it effective?

No. In general, the detection thresholds are excessively high for water from a cooling tower (100 CFU / ml), which makes it a qualitative test.

37. Does every water treatment company offer a detection program?

No. Few offer the service and even less do it through their own resources.