Are we losing the battle against Legionnaires’ Disease?

While one would hope Sydney’s recent outbreak of Legionnaires’ Disease is an isolated incident, the fact is that over 50 cases have been reported this year.

As a result, two people have died in the past two months. According to the Sydney Morning Herald, there have been more cases of Legionnaires’ Disease between January and April this year than any year since 2012.

Knowing that any one of us could be in danger without even realising it, this begs the question: what is being done to prevent Legionnaires’ Disease and why isn’t it working, asks Stephanie Stefanovic.

The Sydney CBD and inner-west suburb of Burwood played host to Sydney’s most recent Legionnaires’ outbreaks, with three and five cases respectively being diagnosed this May.

The NSW Health Department believes that polluted cooling towers are the culprit of these outbreaks.

This has been supported by the fact that 15 out of 387 cooling towers in the CBD tested positive for Legionella in mid-May (almost 4 per cent), although there were no positive test results for any of the towers tested in Burwood at the time this article was written.

Further testing is currently taking place in neighbouring areas, according to Jeremy McAnulty, Acting Chief Health Officer at NSW Health.

It is easy to understand why cooling towers are being blamed for the spread of the disease. Essentially, cooling towers are used to cool water and dissipate unwanted heat to the atmosphere through water evaporation.

Specifically, warm water flows into the top of the cooling tower through spray nozzles, during which time tiny airborne droplets are formed, providing maximum contact between the water and the air moved through the tower by fans.

While falling through the tower, some of the water evaporates and because this process consumes heat, the water remaining in the tower is cooled.

The problem is that circulating air and water and water heated via heat exchange create an ideal environment for Legionella to grow.

This is also amplified if there is any algae or scale present in the water. Furthermore, Legionella can then be easily dispersed into the air with the aerosolised drift and evaporate, and can even enter the air-conditioning system if there is a break between the ducts and those of the cooling tower.

If either of these situations occur, people are liable to breathe in the bacteria and contract Legionnaires’ disease, resulting in a range of health problems including pneumonia and possibly even death, as was seen in two Sydney cases this year.

Of course, the presence of Legionella in cooling towers can be prevented or minimised with good engineering practices in the operation and maintenance of the towers.

In Victoria, the Public Health and Wellbeing Act (2008) and Regulations (2009) require that cooling towers are continuously treated with a biodispersant, anticorrosives and more biocides. It is also recommended that indicators of infection (such as the concentration of biocides, pH, conductivity and water temperature) are monitored on a monthly basis, with Legionella testing being legally required every three months.

In NSW, the legal requirements are somewhat less strict. Cooling tower maintenance falls under local government rather than State Government as it does in Victoria, and there are no specific regulations around the exact combination of chemicals that must be used to control the growth of bacteria, rather tower owners must “demonstrate the disinfection process used adequately controls microbial growth”, and complete Legionella testing every six months, according to the Public Health Act (2010).

However, it is worth noting that Victoria has a greater history of Legionnaires’ outbreaks than NSW, which is likely the reason for their stricter regulations.

Sydney’s growing Legionnaires’ problem suggests that NSW may need to take Victoria’s lead in regard to cooling tower maintenance regulations.

According to Glen Pinna, manager of Biotech Laboratories in Brisbane, the value of testing water samples for Legionella is one of the most controversial health issues of building air quality.

This is because while laboratory testing can be invaluable in preventing Legionnaires’ outbreaks, there is scientific evidence suggesting that the accuracy of these tests is questionable.

According to Pinna, when testing free-flowing water, there is great potential for inaccuracy. This is because bacteria are not perfectly distributed in the water, of which only 0.23mL is tested.

Therefore, it is unrealistic to expect such samples to be representative of the entire water-cooling system. What’s more, despite the fact that all water samples are sent to nationally accredited laboratories using the same Australian Standard method, there is potential for significant variation in the results simply due to the effect of transport time and temperature on the samples, as well as the competency of the staff and the quality of the culture media.

On the other hand, there is no doubt that acting upon a positive test result could be instrumental in preventing an outbreak of Legionnaires’ disease.

However, it is worth noting that Legionnaires’ outbreaks are almost always the fault of poor maintenance and control of the cooling systems infected with Legionella, rather than the absence of testing, according to Pinna.

This suggests that NSW local governments may be dropping the ball on cooling tower maintenance, and perhaps this responsibility should fall on State Government as it does in Victoria, according to Opposition health spokesman Walt Secord.

Furthermore, it suggests that NSW may need to follow Victoria’s lead in creating more stringent regulations around cooling tower maintenance.