Legionella bacteria can cause Legionnaire's disease in humans. Well known sources of these bacteria include cooling towers, whirlpools and plumbing installations, but PhD Candidate Eri van Heijnsbergen has discovered that Legionella bacteria can also be found in garden soil and puddles of rain water. For most Legionnaire's disease patients, the source of the infection is never found, possibly because the natural environment is not considered in the search for the source. According to van Heijnsbergen, future source investigations should take this into account.
Legionella pneumophilia-ST47, an important cause of disease in the Netherlands, has been found in garden soil. This type of Legionella bacteria has only been found in source investigations three times since 2002. In all cases, the source was a whirlpool located in a garden. This strain of the bacteria may have entered the whirlpool from the garden soil, and caused an infection from there.
Van Heijnsbergen also found other types of Legionella pneumophilia in soil samples, several of which had been observed in patients in the past. She also showed that Legionella bacteria can survive in the soil for long periods, and that there is a relationship between the types of soil and the presence of Legionella. Puddles of rain water also contained Legionella bacteria, but not as often as the soil samples studied.
“It is still unclear whether a Legionella infection can occur via the soil or puddles”, says van Heijnsbergen. “But we suggest that soil samples be taken when investigating the source of an infection, especially for the strains of Legionella that are commonly found in soil.” According to the PhD Candidate, further research is needed into two other known sources of Legionella bacteria: cooling towers and sewage treatment plants. “At the moment, these systems are not routinely included in source investigations”, she explains. “So they may be underestimated as a cause of Legionnaire’s disease in the Netherlands.”