I apologise to the Solar Trade Association for following their “line” that there are no cases of Legionella attributable to solar water heating, because here is some extra news.

I was mistaken. If the solar industry ever claims to the public that there are no cases of Legionella linked to solar thermal, their claim is mistaken. In fact there was a major outbreak as long ago as 13 years ago in Antigua. There is also new evidence linking solar and Legionella   from Turkey.

The claim that any risk is negligible is not supported by the evidence either. Indeed people may even be dying now, with the figure depending on what increased risk, if any, really attaches to solar thermal.

1/ Direct attribution of Legionella infection to solar water heating apparently exists.

Here is a case of Legionella which is apparently attributable to solar. I quote from:

http://www.q-net.net.au/~legion/Legionnaires_Disease_England_Wales_1996.htm

“Outbreak III The first outbreak of legionnaires’ disease ever associated with the Caribbean island of Antigua was detected in October 1996. Two cases occurred in September and one in October 1996. All had stayed at a hotel complex in Mamora Bay. The PHLS and the Caribbean Epidemiology Centre (CAREC) were invited by the Ministry of Health of Antigua and Barbuda to carry out environmental and epidemiological investigations into the source and extent of the outbreak. The hotel’s sickness records showed that the incidence of respiratory illness was higher than expected among staff in August and among guests in September, suggesting that the outbreak had been triggered by a single event. This event was found to be the installation in August of a solar powered hot water system at the hotel. Thirty-one out of 54 hot and cold water samples from the hotel’s water systems were positive for legionella and 19 of these contained L. pneumophila sg 1. Isolates from the hot water tap in a room where one of the cases stayed, the solar hot water storage tank drain, the gymnasium shower, and the spa pool filter housing were all indistinguishable by monoclonal antibody (mAb) subgrouping and restriction fragment length polymorphism (RFLP) typing from a clinical isolate obtained from one of the cases in the outbreak. A serological survey of 11 of the 35 hotel staff who reported a respiratory illness between August and November revealed two people who were retrospectively diagnosed as presumptive cases of legionnaires’ disease with single high titres of antibody against legionella. A questionnaire was sent to 21 guests from the UK, France, Germany, and the US who had reported a respiratory illness while at the hotel in September. All were asked to take part in the serological survey but none was found to have evidence of legionella infection. Several national and international tour operators stopped sending guests to the hotel when the outbreak was identified in November and did not return to the hotel until December when all investigations and control measures were completed.”

So if this website is correct, then Legionella has in fact been directly attributable to solar thermal installations. That installation did in fact need control measures. One wonders if they included heating to the base of the hot water cylinder.

So the very first recorded outbreak in Antigua had a solar water heating cause. This event took place over a decade ago, so our industry almost certainly knows about it. One wonders whether the “control measures” referred to included regular heating to the base of the calorifier (as L8 guidance requires). Do any readers know? I’d like to see the original documentation.

There also appear to be cases of Legionella infections being linked to solar thermal in Turkey.

2/ Numbers of people infected with Legionella in UK are not as low as claimed.

A senior medic involved in Legionella tells me that the:

Nottingham Legionella study, a definitive prospective study, showed that 2 to 3% of community acquired cases of pneumonia (CAP) are attributable to Legionella (a separate independent study by others that came up with a similar percentage). So at approximately 300,000 cases of CAP per annum in the UK we should then see around 7,500 cases of Legionella d. (LD) per annum (i.e. using 2.5% as the incidence of LD amongst CAP’s). In practice we only see about 400 cases of LD reported to the HPA per annum, so the maths tell us that we miss about 95% of all cases of LD.

There is not a coroners inquiry for every death caused by pneumonia, and in many cases not even a postmortem (PM), if there has been a history of respiratory problems, which invariably is a precursor to LD. Pneumonia can be diagnosed at PM but LD can’t without specific lab tests, and these can be very unreliable after death. So LD is normally missed in life and at PM.

In 2006 there were around 295,000 cases of CAP reported in the UK, but in only approx 7,000 of these was the microbiological cause of the pneumonia identified. So with a background of poor ascertainment of the cause of CAP you can see why we are likely to miss the more elusive LD (which is classed as an ‘atypical’ pneumonia) and why just ‘pneumonia’ is all that is normally entered in the case notes or on the death certificate.”

So there are 7,500 cases per year in UK alone. (not 400) How many in solar properties? How many deaths?

As a rough calculation the EU solar trade body ESTIF say there are 400k sqm of solar collectors in UK right now. So at say 4 sqm per property this is 100k solar properties. Let’s assume that 80% don’t heat daily to the base of their hot water cylinder, but only partway down (which is a noncompliance with HSE guidance on Legionella. Assuming there are about 25M properties in UK then the solar market penetration of noncompliant systems is 0.32%. Therefore if solar delivered no increase in risk, (which it arguably does) there are 24 cases of Legionella on solar properties already.

If the solar risk factor were to be only double that of normal then the increase in infection attributable to solar would be 24 which must be reduced by a factor which reflects the domestic hot water origin of infection, rather than other origins, a figure which I will assume (please give me a more accurate figure if you can supply this and any others) to be 50%. So even now there may be 12 extra cases. At an 8% death rate (real rates may be higher) this already means about 1 (avoidable) statistical solar-attributable death a year.

But what if the risk factor was not double but say 6 times extra? We do not know if this figure is correct or not, But Dr Tom Makin says that conventional solar is “highly likely” to be creating a risk (and a rather small Danish study which found Legionella was 6 times more common in hot water from solar homes than in non solar homes). Then, if this 6 times more figure were correct, we would be looking at about 5 deaths a year, nearly one every two months from UK’s existing solar water heating installation.

Over a human lifetime of 80 years, this risk may add up. And this is just in UK – imagine the much larger German position. What if UK were to meet the govt’s target of 7 million solar homes instead of today’s 0.1M solar homes that we have now? It may be wise to think ahead. I hope this bit of science followed by calculations which are nevertheless based on several assumptions at least informs the debate. I emailed these very figures to a long standing STA board member with whom I had been in correspondence. He promptly wrote a “disclaimer” and ended our debate.

We surely all hope that any increased risk of our competitors’ lax approach to solar water heating design delivering Legionella infection to anybody is nonexistent. But the evidence is increasingly not pointing in that direction. This issue must not become the silent solar thermal industry killer (or disabler) of people in the same way that carbon monoxide from poorly installed or maintained boilers can kill and disable people. We at Solartwin don’t take the same risks – we minimise them.

Regards, Barry.