Tuesday, 8 May 2012

Compost, potting mix and Legionnaire's Disease ~

Legionnaire's disease is relatively rare but it is serious and can be fatal.  It can be caused by the inhalation of dust or water vapour which carries legionella bacteria.  Fortunately these bacteria don't affect everyone but it is as well to be alert to the possibility.  These bacteria can live in many watery environments and if conditions are right they can breed and become problematic.

Common trouble spots are compost and potting mix and air conditioning cooling towers.  They may also be found in residential hot water cylinders, spa pools and even the water in windscreen cleaning containers in vehicles!  For this reason it's sensible to maintain recommended levels of hygiene and to handle compost with care.

I'm a keen gardener and love my compost heap but I am now much more careful about how I handle it than I used to be: our elderly neighbour, Walter, nearly died after inhaling legionella bacteria from freshly opened bags of compost. Swabs taken from empty bags and examined in a laboratory confirmed them as the source, so the warnings printed on such bags are meant to be taken seriously.

Once the harmful bacteria have been inhaled symptoms can take a week or so to manifest.

In the week after Walter composted his vegetable patch he developed what seemed to be a heavy cold which got steadily got worse.  Some ten days later when he was just about to leave home for a doctor's appointment he collapsed.  His wife shouted out to me to come over quick, and it was fortunate that I had the front door open and heard her.  I ran over to find him on the floor, still conscious but very hot and quite unable to get up.  He's a big man and we couldn't move him at all, so having tucked some cushions in behind him called the emergency services.

The fire people were the first to come as they were the emergency service closest to hand.  They were followed by the ambulance.  It was a singularly nerve-racking time and I was very relieved to see them and glad to relinquish responsibility.  They were marvellous: very strong, healthy and reassuring.  One of the firemen was sporting a black eye which he joked about with Walter, but although he responded with good humour he was very ill indeed and has no recollection of that time at all.


Once in hospital he was put into an induced coma and expectations of his survival were slight.  He was out cold for ten days hovering between this world and the next, but against all the odds he did pull through, regaining consciousness just when all hope was being given up, and gradually began on the long, slow road to recovery.  We were all astonished as we had been expecting the worst!  When he came home I told him how glad I was to see him as I'd been worrying about what I'd wear to his funeral!  I'm pleased to say that he found this amusing and we both had a good laugh, but was true enough all the same.

News items:
Walter's illness followed a very similar course to this man's:
Since then there has been an outbreak in Central Auckland.  The source of the bacteria can be difficult to locate as the bacteria can be blown up to six kilometres!
Autumn can be a time when infections of this sort crop up more often as people busy themselves with tidying up their gardens before winter.  In New Zealand this coincides with Easter. 
This Ministry of Health (NZ) publication gives detailed information about prevention:
The information conveyed by this web page is comprehensive and much of it is technical.  Fortunately it has a good index; unfortunately it has been placed in document form only, so the reader has to download it in order to read it.  For these reasons I quote two passages directly from this source (as their copyright permits) for easy reference:
The following excerpt relates to the safe handling of compost and potting mix:
 7.1.4.1 PreventionThere is no statutory requirement in New Zealand that potting mixes and other compost materials must have warning labels attached. This is because most manufacturers have volunteered to use an industry-agreed warning label (Figure 16) as recommended by NZS 4454: 2005 Composts, soil conditioners and mulches. To prevent Legionella infection from potting mix and other compost materials, people should take precautionary steps, including the following.
  • Open potting mix bags using scissors with care to avoid inhaling airborne potting mix, ie, slowly and away from the face.
  • Moisten the contents of the bag on opening, by making a small opening and insert a garden hose to dampen the potting mix.
  • Avoid potting-up plants in unventilated areas, such as enclosed greenhouses.
  • Wear gloves.
  • Avoid transferring potting mix from hand to mouth (eg, rubbing face with a soiled hand or glove).
  • Wear a face mask if handling soil, mulches, compost or potting mix indoors or in windy conditions.
  • Always wash hands after handling potting mix, even if gloves have been worn, as Legionella bacteria can remain on hands contaminated by potting mix for up to one hour.
  • Store potting mix in a cool place, away from the sun.
  • Keep soils and potting mix damp.
  • Avoid raising soil near evaporative coolers.
  • Water gardens and composts gently, using a low-pressure hose.
  • When handling bulk quantities of potting mixes or other soil products, follow procedures that minimise dust generation.
Face masks should be either P1 or P2 particulate masks, as specified in AS/NZS 1715: 2009: Selection, use and maintenance of respiratory protective equipment, or AS/NZS 1716: 2003: Respiratory protective devices. It is recommended good practice for retailers of potting mix and compost to also offer protective masks at point of sale. 
The following information from the same document relates to the storage of both hot and cold water:
6    Hot, warm and cold water systems
6.1 General
Summary control of temperature
  • The recommended temperature for storage and distribution of cold water, to prevent Legionella infection, is below 20 degrees Celsius.
  • Store hot water above 60 degrees Celsius.
  • Ensure hot water at the outlet of all sanitary fixtures used primarily for personal hygiene purposes is delivered at a temperature not exceeding:
    • 45°C for early childhood education centres, primary and secondary schools, nursing homes or similar facilities for young, sick, elderly and disabled people, institutions and hospitals
    • 55°C for other buildings.
Other informational links which may be of interest:

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