Friday 13th September 2013, 7:40PM BST.
A health board is investigating four cases of the infection Legionella longbeachae linked to gardening compost.
Two patients are being treated in intensive care while two more have been discharged from hospital, NHS Lothian said.
The four people affected are keen gardeners between the ages of 62 and 84-years-old.
Dr Richard Othieno, NHS Lothian consultant in public health and chair of the incident management team, said: “This type of Legionella is quite rare in that unlike other strains it has never been identified in man-made water systems, like cooling towers.
“We are working with experts to trace the source of the infection and samples of the compost have been sent for testing.
“We know that each of the four cases are keen gardeners and had purchased different products containing compost prior to acquiring the infection.
“Gardening is a healthy hobby but there are risks and it is important that people take some simple precautions when working in their garden or with gardening products.
“I would like to add further reassurance that the risk to the wider public is low.”
The symptoms of Legionella longbeachae include headaches, diarrhoea or a dry cough followed by pneumonia.
Most people recover after treatment with antibiotics but those with underlying medical problems are more vulnerable, the health board said.
It is not known exactly how the infection is passed from compost to people but health experts assume it is through breathing in very small dust particles or drops of contaminated water. The infection is not transmitted from person to person.
Anyone handling garden materials such as potting mix, mulches, composts or garden soils is advised to open bags carefully, wear gloves and keep doors to greenhouses or sheds open when potting plants or filling hanging baskets.
Gardeners are also advised to wear a mask if the air is dusty, particularly indoors, and to wash their hands immediately after using compost and before smoking.
There is no link between the current cases and the outbreak of Legionella pneumophila in south west Edinburgh in 2012, NHS Lothian said.