Legionella longbeachae serogroup 1 infections linked to potting compost.

Four cases of legionellosis caused by Legionella longbeachae serogroup (sg) 1 were identified in Scotland from 2008 to 2010. All case patients had exposure to commercially manufactured growing media or potting soils, commonly known as multipurpose compost (MPC), in greenhouse conditions, prior to disease onset. Two patients had been using the same brand of MPC but the clinical isolates were distinct genotypically by amplified fragment length polymorphism (AFLP) analysis. However, an indistinguishable AFLP profile was also found in an environmental isolate from the supply of MPC used by each patient. The third patient was diagnosed by immunofluorescent antibody serology only; however, the MPC to which this patient was exposed contained L. longbeachae sg 1 in large quantities (80 000 c.f.u. g(-1)). The fourth patient was L. longbeachae sg 1 culture-positive, but L. longbeachae was not identified from 10 samples of garden composting material. As compost is commonly used, but L. longbeachae infection seemingly rare, further work is required to ascertain (i) the prevalence and predictors of L. longbeachae in compost and (ii) the conditions which facilitate transmission and generate an aerosol of the bacteria. As most cases of legionellosis are diagnosed by urinary antigen that is Legionella pneumophila-specific and does not detect infection with L. longbeachae, patients in cases of community-acquired pneumonia with a history of compost exposure should have serum and respiratory samples sent to a specialist Legionella reference laboratory for analysis.