Dr Surani McCaw, a healthcare consultant and adviser on water sterilisation standards, outlines the critical factors for success when using temperature to control biofilm.

The effect of temperature on the control of biofilm is commonly misunderstood due to misconceptions, lack of knowledge or experience.  Due to numerous studies available, as well as lessons learnt on Legionnaires’ disease related to past Legionella outbreaks, the current Australian guidelines for Legionella control in hospitals are now required to operate at controlled temperatures of ≥ 55oC.

Many of the environmental factors that encourage Legionella growth also encourage the growth of mycobacteria and other gram negative bacteria such as Pseudomonas.  Therefore, without the adaptation of a holistic approach in the control of microorganisms, these pathogens can thrive in the water distribution systems in our hospitals.

Some of these common but harmful bacteria can proliferate in our nutrient rich municipal water networks when operating between 25 and 45oC.

Although it is well documented that hospital water systems operating at temperatures greater than 55oC reduce the proliferation of Legionella, the proliferation of thermotolerant or heat-resistant bacteria at these temperatures is not well published.

When using temperature to control microbial growth, the only scientifically proven and validated process for disinfection is the application of water for a minimum holding time at temperatures between 80 and 90oC. Temperature, as well as holding time, is critical in achieving the required disinfection outcomes.

For example, where A0 principle is applied as per ISO 15883, to achieve A0 value of 3,000 when constant temperature of 80oC is used, holding time of 50 min is required. When a constant temperature of 70oC is used, holding time of 500 mins is required. At our busy hospitals, a 500 min holding time for disinfection is not practical. Hence, when employing thermal disinfection it is critical that the temperature at every point within the purified water plant is maintained at greater than 80oC. Please note that although A0 value of 3,000 is used as an example here, this value may not be suitable for all systems and applications to achieve the required disinfection outcomes.

Where purified water plants are required to operate between 35 and 45oC, such as for Endoscope Reprocessing, or at ambient temperature or 65oC for CSSD, greater care with a proactive approach using automatic thermal disinfection between 80 and 90oC is paramount even in the control of water borne diseases such as Legionnaire.

If thermal disinfection is not applied correctly using evidence and science based good practices, the final patient outcomes can be catastrophic.


By Dr Surani McCaw, B.E. (Chemical)
Southland Filtration