Bags of compost sold in the UK may be a significant source of Legionella bacteria, including strains that cause human disease, say scientists.
Tests on 22 brands of compost available in the UK found that 14 contained a variety of Legionella bugs.
Four showed evidence of Legionella longbeachae, which can cause serious infections leading to admission to hospital or death.
Dr Tara Beattie, from the University of Strathclyde in Scotland, who led the research, said: "Disease causing micro-organisms are widespread in the environment, and therefore it is not too surprising that species of Legionella that can cause human disease are present in compost.
"Any environment where you have pathogenic bacteria could be a source of infection, and we already know that compost has been linked to human Legionella infection in countries such as Australia and New Zealand.
"Within the UK and across Europe composts have traditionally been composed of peat, whereas sawdust and bark are more often used to produce compost in Australia and New Zealand where Legionellosis associated with compost is more common.
"It may be that the change in composition of composts in the UK, moving away from peat based products, could be resulting in species such as Legionella longbeachae being present in compost and therefore more cases of infection could occur."
The findings are reported in the journal Clinical Microbiology and Infection.
Last month health experts recommended putting warning labels on compost bags after a spate of Legonella longbeachae infections in Scotland.
Five people have been affected since the outbreak began in August. The latest victim was being treated in hospital in Dundee two weeks ago.
Dr Beattie said: "A larger scale survey, covering a wider range of compost products is required to determine if these organisms, some disease causing, some not, are as widespread in composts as this initial study would suggest.
"It should be emphasised though, that although Legionella seem to be common in compost, human infection is very rare, especially if you consider the volume of compost sold and used.
"But with any potential source of infection precautions should always be taken. The occurrence of these bacteria in composts in Australia and New Zealand, and the cases of infection that have been traced to compost has resulted in hygiene warnings on compost packaging in these countries, and this is something manufacturers in the UK may wish to consider."