Storms, Seasons, Stagnation and Legionella Stats!
Several environmental factors will influence Legionella isolations and incidences of disease. The normal changes of temperature with seasons is one factor. Disruptive weather patterns such as severe storms and heat waves are others. All have the potential to create stagnation and trigger Legionella growth and distribution through water systems. So what does this mean for your facility?
Stagnation is a major contributing factor for Legionella detections and cases of disease. The role of biofilms in the stagnation process has been discussed in another blog. In this section we’ll look at how the environment can also influence stagnation and biofilm detachment. We are for the most part at the mercy of the prevailing weather. Three different features of our weather patterns will influence Legionella growth and movement through water systems. Ultimately this leads to human exposure and the potential for disease. So how do these weather processes end up with stagnation and biofilm detachment?
Severe storm activity has two major affects. Firstly heavy rainfall puts pressure on water utilities and can cause unavoidable deterioration in water quality. Although in most cases the water supply is safe to drink it may contain increased nutrient levels that stimulate growth of microorganisms. This in turn can reduce how long disinfectant residuals will remain active along the pipe lines. Flooding may also damage pipe infrastructure and allow entry of untreated water. This may not be detectable by smell, colour or taste but may seed microorganisms into the system.
A second indirect factor is power outages. During the now famous (or is that infamous?) statewide blackout in South Australia in 2016 major infrastructure in water distributions stopped operating. Pipelines were stagnant for up to 6 hours. Once water begins to move again the biofilm detachment process starts.
Source: ABC News. 29 Sept 2016
Power outages may also make water heaters lose temperature, and circulating pumps and dosing equipment fail. Inevitably this leads to stagnation. Once power resumes the biofilm detachment cycle begins again unless a residual disinfection process is in place. A comprehensive Water Safety and Risk Management Plan should have a contingency plan for dealing with disruptions in power and water supply.
Just after the storm blackout the SA Health Department put out a notice to Environmental Health Officers and Water treatment Providers that building supplies may be compromised by these events (see below).
“Dear Environmental Health Officers and Water Treatment Service Providers
Re: Legionella risk management following recent power blackouts and extreme weather
Following the SA power outage on 28/9/16 and recent severe weather conditions, there is the potential that the safe and effective functioning of high risk manufactured water systems may have been compromised by power outages and / or storm damage.
This email is being sent to promote the inspection of high risk manufactured water by system owners/operators, nominated responsible persons or water treatment service providers to ensure their safe operation and compliance with the South Australian Public Health (Legionella) Regulations 2013 (the Legionella Regulations).” – SA Health, Public Health Services 06/10/2106
An obvious effect of heat waves is water getting warmer! Particularly cold water can reach ideal temperatures for Legionella growth. Cold water pipes without lagging in roof areas will commonly reach these temperatures during hot weather. Less obvious is the use of misters / sprinklers and paddling pools to cool off. Attention to these devices is important. Using clean water for misters and sprinklers and draining pipes after use is recommended. It is best to empty paddling pools after use. If stagnant they can quickly become infected with protozoa that can cause fatal disease in children and immune compromised as well as promote growth of Legionella and other bacteria.
Source: Bentham, 1993
The seasonal nature of Legionella colonisation in cooling towers is well known (see left). It is also well known that late summer is a high risk time for outbreaks from these devices. By the end of summer cooling towers have had plenty of time for Legionella to establish. After a period of cool weather when cooling towers are not operating there is stagnation. A late ‘indian summer’ makes cooling towers fire up again blowing the detached biofilm and Legionella into the environment. This phenomenon was first demonstrated in the field in a South Australian study in the early ’90’s.
This seasonal effect is also mirrored by Autumn peaks in Legionnaire’s disease cases. However the effect is not quite so strong in potable water systems. This is because environmental conditions have less direct impact on potable water systems. Design and thermal control in the the building have greater effects on the system. Water heaters, mixing valves, dead legs, aerators and a multitude of other plumbing infrastructure play a more significant part. All these components can create opportunities for stagnation and need maintaining. For this reason disease cases in potable water systems are much less seasonal. That is not to say that storms, heat waves and water quality are not important contributing events. So constant vigilance and an active Water Safety and Risk Management Plan are critical.
Bentham R (1993) Environmental Factors Affecting the Colonization of Cooling Towers by Legionella spp. in South Australia. International Biodeterioration and Biodegradation 31:55-63
Bentham R, Broadbent C (1993) A model for autumn outbreaks of Legionnaires’ disease associated with cooling towers, linked to system operation and size. Epidemiol. Infect. (1993), 111, 287-295