It has recently come to my attention that working with potting mix comes with some health risks that no one has ever told us about. Because the soil is typically stored in a plastic bag — often in the sun — it provides the perfect breeding ground (warm and moist) for bacteria and fungi. Normally, this wouldn't cause a problem, but when that bacteria is legionella bacteria, it can lead to legionnaire's disease, a potentially fatal form of pneumonia.
Reports of deaths from legionella bacteria are primarily from Australia and Japan, but are not unknown in the United States, explains a 2000 CDC report.
A July 2017 report by the CDC also lists commercial bags of compost as a possible source of the legionella bacteria. Some commercial potting mixes (and compost) tested in the US have tested positive to legionella bacteria, the CDC further explains.
While the risk appears to be higher in Australia where 73 percent of the soil samples tested contained legionella, gardeners in the U.S. should be aware of the risks associated with opening and using bags of potting soil or compost.
How do you get Legionnaire's disease?
It is believed that inhalation of the bacteria is the primary means of infection, but the CDC has not ruled out contact with the skin.
Who is at the greatest risk?
People with respiratory disorders, such as COPD, those with compromised immune systems and the elderly are at the highest risk, but that doesn't mean it can't infect younger and healthier gardeners, too.
How do you prevent contamination?
Observe the following recommendations to reduce the risk of exposure to the legionella bacteria.
I'm certainly not recommending that you avoid potting soils and compost completely, but never hurts to be cautious, especially if you are at a high risk due to health and/or age.