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Censorship news: massive solar Legionella cover-up revealed today by Freedom of Information Inquiry.

Filed under: Latest News

It is “highly likely” that some older types of solar hot water system installation “are creating a health risk” acording to files revealed today under a Freedom of Information Request made to the UK Government’s Department for Environment and Rural Affairs. Concerted industry pressure seems to be preventing the public from reading important expert medical opinion on solar heating and Legionella to the extent that that the public have been cynically and deliberately prevented from being told that several older designs of solar water heating systems fail to comply with Health and Safety Executive guidance on Legionella.

Apparently cut from publication on the website of the Water Regulations and Advisory Service (WRAS) is a critical document written by a senior medical expert on Legionella, Dr Tom Makin of Royal Iverpool University Hospitals. Dr Makin examined the risks of Legionella in Solar Heating or Heat Pump systems. Its penultimate sentence reads (I have added bold to 7 words):

It is therefore highly likely that those solar pre-heating water systems which support the growth of legionella bacteria and do not achieve thermal inactivation or control of legionella bacteria in some other equally effective way, are creating a health risk with regards to legionella infection

Barry Johnston, Managing Director of Solar Twin Ltd commented today: “One is forced to ask about the competence of Government who are prone to stupid cover ups which are then revealed. For example, why has Government apparently permitted this crucial document to be covered up, despite its potential public health importance? Is it that UK’s government regulators are too besotted with placating certain trade bodies to take consumer interests seriously? Or are they seeking to bankrupt and thereby silence the minority of installers of safer solar technologies by excluding their customers from gaining state funds such as grants and subsidies? We have been explaining for years that it is unfair to the consumer that simple, safer solar designs, such as ours, and those of several other conscientious suppliers, are unreasonably excluded from grant aid. It is clear that many old solar installation approaches are capable of being radically improved from a safety perspective and that the solarr industry is seeking to block progress on possible issues of public safety.”

The text of the full report is given below. We have added bold to emphasise some key points.

LEGIONELLA BACTERIA AND SOLAR PRE-HEATING OF WATER FOR DOMESTIC PURPOSES

Report by Dr T Makin for the Water Regulations Advisory Scheme.

Dr T Makin, Directorate Manager, Medical Microbiology, Medical School, Royal Liverpool University Hospitals Co-author of the HSE ACoP and Guidance (L8), and the Health Technical Memorandum HTM04-01 providing guidance on the control of legionella bacteria in health care premises.

1. Legionella bacteria are ubiquitous in all water systems and their growth occurs at temperatures in the range of 20 to 45OC. Hot and cold water systems (HCWS) are particularly prone to colonisation by legionella bacteria and these water systems are now recognised as the commonest source of Legionnaires’ disease. Temperatures within the range of 20 – 45OC are commonly present at the base of calorifiers and other hot water storage vessels. Suitable growth temperatures and the accumulation of sediments of organic material and corrosion products at the bottom of hot water storage vessels provide an environment that is especially conducive to the accumulation of biofilm and legionella bacteria.

2. Control of legionella bacteria in hot water vessels and in peripheral parts of the distribution system can be achieved through raised temperatures. Thermal inactivation of legionella bacteria commences at 50OC, and at 60OC it is generally reported that the majority of legionella bacteria are killed within a few minutes. Where recommended temperatures are not achieved in hot water storage vessels, legionella bacteria normally resident at the base of the vessel may enter the distribution system and be directly discharged at outlets in the form of infectious aerosols. Viable legionella bacteria that escape thermal inactivation in calorifiers can colonise peripheral parts of the distribution system, and these become important secondary reservoirs of contamination within the HCWS.

3. One of the most comprehensive studies carried out on thermal inactivation of legionella bacteria was undertaken by Janet Stout et al. This study determined the D value for the various strains of legionella bacteria tested. The D value is the time required to kill 90% of the legionella bacteria exposed to a specific temperature. For example, a D value of 10mins at 60OC (D60OC = 10min) indicates that an exposure time of 10min is required to reduce the concentration of a suspension of organisms by 1 log (i.e. by 90%). Other recognised studies on thermal inactivation of legionella bacteria have not been as wide-ranging with regards to the number or diversity of legionella strains tested, but the more pertinent of these investigations reached similar conclusions to those arrived at by Stout et al (Schulze-Robbecke R et al, and Dennis PJ et al).

4. Stout et al. carried out thermal inactivation studies on a range of legionella bacteria including eight serogroups of Legionella pneumophila (40 strains) and nine different Legionella species (34 strains). Although there was a range of D values for the various strains of legionella tested, these ranges were generally narrow and were similar across the different serogroups of L. pneumophila and the various Legionella species, with the exception of L. micdadei which was more thermotolerant than other legionella bacteria tested. Over 90% of cases of Legionnaires’ disease are caused by L. pneumophila.

5. The D60OC values for L. pneumophila and other Legionella spp (with the exception of L. micdadei), ranged from 2.3 to 5 mins. The mean D60OC value for L. pneumophila was 3.2 mins. The D60OC for L. micdadei was 4.5 to 10.6min, confirming this strain’s thermal tolerance. In this study there was no observable difference detected between D60OC values for clinical and environmental strains of legionella bacteria, or for L. pneumophila when suspended in sterile hot water or in sterile hot water containing calorifier deposits.

6. Any hot water storage vessel displaying thermal stratification and maintaining temperatures in the range of 20 to 45OC is very likely to contain legionella bacteria in significant numbers, unless regular pasteurisation of the entire contents of the vessel takes place at temperatures of 60OC or above. Solar pre-heat cylinders that are subject to thermal stratification would be equally susceptible to legionella contamination. Solar heated vessels that do not reach 60OC and notably those maintaining temperatures below 45OC would be particularly prone to contamination with high levels of legionella bacteria. Where these devices supply water via a combi-boiler in order to raise the hot water temperature to 60OC, then according to the work of Stout et al., the boiler would need to maintain the water temperature at 60OC for 3.2 mins to reduce the concentration of legionella bacteria by 1 log (90%).

7. In my experience, concentrations of legionella bacteria in the range of 105 cfu/l and higher are not uncommon at the base of hot water vessels where temperatures of 20 – 45OC are maintained. If a combi-boiler receiving water from a solar pre-heat cylinder contaminated with legionella to 105cfu/l, maintained a water temperature of 60OC for 3.2 mins this would reduce the concentration of viable legionella bacteria by 90% to 104cfu/l. This significantly exceeds the lower permitted limit of 102cfu/l for legionella bacteria in hot and cold water systems as recommended in the HSE Approved Code of Practice and Guidance on the control of legionella (L8). It also exceeds the upper limit of 103cfu/l at which level remedial action is required, including disinfection of the water system. Water with this level of contamination would need to be heated for an additional 3.2 mins to further reduce the legionella concentration from 104cfu/l to 103cfu/l. Consequently, a concentration of 105cfu/l of legionella bacteria would require exposure to 60OC for approximately 10mins to reduce the number of viable cells to below the threshold recommended in L8.

8. Other more thermo-tolerant legionella bacteria such as Legionella micdadei would require still longer exposure to this temperature before being inactivated. The HSE recommendation to achieve a temperature of 60OC in all parts of hot water storage vessels for a period of one hour daily, has taken into account the higher concentrations of legionella bacteria that may be present at the base of these vessels, and has also made allowance for the more thermotolerant species and for the protection afforded to legionella bacteria by deposits that accumulate in hot water storage vessels. Daily pasteurisation is proposed in L8 in order to control legionella bacteria that may survive this process (e.g. those protected within amoebal cysts or deeply embedded in scale deposits).

9. Solar pre-heat cylinders that maintain a temperature of 60OC throughout the storage vessel for a period of one hour daily should achieve satisfactory control of legionella bacteria. In systems where combi-boilers receive water from solar pre-heat cylinders that are not able to raise the water temperature to 60OC or above, then consideration should be given to programming the system to automatically activate the combi-boiler to heat the water to 60OC and recirculate this through the pre-heat cylinder, at a pre-set time daily.

10. This should provide effective pasteurisation of legionella bacteria colonising the pre-heat cylinder. Where this pasteurisation programme is in place, the volume of potentially contaminated water that can pass through the heating system before a temperature of 60OC is reached (approx 20 litres), should then present little risk of legionella infection. If this pasteurisation programme occurred daily, shorter contact times of less than one hour may still prove effective in controlling legionella bacteria in solar pre-heat cylinders, particularly in smaller systems. Alternatively, as legionella bacteria grow relatively slowly, even when at optimum growth temperatures, then less frequent cycles of pasteurisation (e.g. twice weekly) where the entire contents of the vessel are maintained at 60OC or above for at least one hour, may also achieve satisfactory control of residual legionella bacteria. However, adopting control procedures that vary from the recommendations in L8 would require validating.

11. In twin coil storage cylinders a solar coil positioned at the base of the cylinder is used to pre-heat the water, and a boiler coil is fitted above the solar coil to raise the temperature of the water at the top of the vessel to 60OC. This arrangement may permit temperature stratification that supports the growth of legionella bacteria at the base of the vessel. If the solar coil does not generate temperatures that bring about thermal inactivation of legionella bacteria, and if the residence time for water in contact with the boiler coil at 60OC is less than that required to effect thermal inactivation, then it would be necessary to provide a further level of control e.g. consideration should be given to programming the boiler coil to heat the entire contents of the solar hot water cylinder once daily, preferably during a period when there is little demand for hot water. Where legionella control is not achieved through raised or lowered temperatures, alternative measures such as the use of appropriate biocides, should be considered.

12. It is worthy of note that prospective studies on the incidence of Legionnaires’ disease have shown that our ability to diagnose this form of community acquired pneumonia is inadequate, and even in countries with effective health services and readily available diagnostic testing, approximately 90% of cases of Legionnaires’ disease are missed. This is partly due to Legionnaire’s disease being a relatively rare form of pneumonia that many GP’s and hospital clinicians will not have encountered before and therefore may mis-diagnose. Furthermore, patients with Legionnaires’ disease can present with a wide range of symptoms some of which (such as diarrhoea) may distract clinicians from the correct diagnosis. Given the particularly poor ascertainment of this disease, and the relatively low number of solar heated hot water systems compared to hot water systems fuelled by more conventional means, there is currently insufficient data available to determine if solar heated systems are a significant source of legionella infection.

13. However, it has been clearly demonstrated in HCWS and in many other varied water systems that Legionellosis (Legionellosis includes Legionnaires’ disease, Pontiac Fever, and Lochgoilhead Fever) can arise from any water system that supports the proliferation of legionella, and which discharges the bacterium in the form of aerosols proximal to individuals who may be predisposed to such infection. It is therefore highly likely that those solar pre-heating water systems which support the growth of legionella bacteria and do not achieve thermal inactivation or control of legionella bacteria in some other equally effective way, are creating a health risk with regards to legionella infection. In the UK, manufacturers, suppliers, installers, and owners of such water systems as solar pre-heating systems, have a statutory obligation to assess such risks and implement measures that will effectively control those risks.

Dr T Makin Directorate Manager Medical Microbiology Medical School Royal Liverpool University Hospitals

Papers cited in this report

Stout JS, Best MG, and Yu VL. 1986.Susceptibility of members of the family Legionellaceae to thermal stress: Implications for heat eradication methods in water distribution systems. Applied and Environmental Microbiology. 52:396-399.

Schulze-Rbbecke R, Rodder M, Exner M. 1987. Multiplication and killing temperatures of naturally occurring legionellas.

Zentralbl Bakteriol Mikrobiol Hyg. 184(6):495-500. Dennis PJ, Green D, Jones BP. 1984. A note on the temperature tolerance of Legionella. Applied Bacteriology. 56(2):349-50.

(Note: over a dozen other documents were released under our Freedom of Information Request. We will publish these also if significant interest is expressed.)


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