Legionella spp. in UK composts—a potential public health issue?

Abstract

Over the past 5 years, a number of cases of legionellosis in Scotland have been associated with compost use; however, studies investigating sources of infection other than water systems remain limited. This study delivers the first comprehensive survey of composts commonly available in the UK for the presence of Legionella species. Twenty-two store-bought composts, one green-waste compost and one home-made compost were tested for Legionella by culture methods on BCYE-α medium, and the findings were confirmed by macrophage infectivity potentiator (mip) speciation. Twenty-two of the samples were retested after an enrichment period of 8 weeks. In total, 15 of 24 composts tested positive for Legionella species, a higher level of contamination than previously seen in Europe. Two isolates of Legionella pneumophila were identified, and Legionella longbeachae serogroup 1 was found to be one of the most commonly isolated species. L. longbeachae infection would not be detected by routine Legionella urinary antigen assay, so such testing should not be used as the sole diagnostic technique in atypical pneumonia cases, particularly where there is an association with compost use. The occurrence of Legionella in over half of the samples tested indicates that compost could pose a public health risk. The addition of general hygiene warnings to compost packages may be beneficial in protecting public health.

Current and Emerging Legionella Diagnostics for Laboratory and Outbreak Investigations

“…1) (30)(31)(32)(33). Several species have also been recovered from composts and potting mixes in the United States, Australia, and the United Kingdom and in the soil of Thai farmland (34)(35)(36)(37)(38)(39)(40)(41). At present, there are ϳ56 distinct Legionella species (and many unnamed species) encompassing at least 70 serogroups, approximately half of which have been isolated from, or detected in, clinical specimens, but all species are regarded as potential human pathogens (42,43).…”

Organic Growing Media: Constituents and Properties

“…Isolation of Legionella longbeachae from growing media based on composted bark in Australia (Steele et al, 1990) and its association with illness in users of such media has led to the insertion of printed warnings on bags of media sold through retail outlets. Legionella longbeachae has recently been detected in growing media, particularly those where peat has been diluted with other materials, in the United Kingdom and associated with illness among users (Currie et al, 2014). However, in both countries and the United States, risk assessments indicate that the likelihood of contracting legionellosis from growing media is very low.…”

Legionella species diversity and dynamics from surface reservoir to tap water: from cold adaptation to thermophily

“…Most Legionella species are of aquatic origin including L. pneumophila; a few are also isolated from non-aquatic habitats such as potting soil and compost (especially L. longbeachae) (Fields et al, 2002;Borella et al, 2005a;Casati et al, 2010;Lück et al, 2010;Whiley and Bentham, 2011;Travis et al, 2012;Currie et al, 2014). Many Legionella species are considered well adapted to low-nutrient conditions in water, and therefore pre-adapted to conditions in drinking water (Vervaeren et al, 2006).…”