From Keith Bremner, Brisbane, Australia
You report that one mechanism by which silver prevents harmful bacteria spreading has been clarified (7 March, p 15). In 1989, and again in 2009, I was too ill to work. It seemed to me that the cause was bacteria and fungi growing in air conditioning ducts in relatively new buildings.
When I worked in buildings constructed before 1980, I had no problem. The ductwork in these was made of zinc-coated steel. The newer ducts were aluminium. Maybe other metals have antimicrobial properties too.
