High prevalence ofLegionellain non-passenger merchant vessels

Abstract

SUMMARYThere is a paucity of information on the risk from potable water in non-passenger merchant vessels (NPMVs) particularly with regard toLegionellaand other bacteria. This retrospective study examined water samples from 550 NPMVs docked in eight UK ports. A total of 1027 samples from 412 NPMVs were examined for total aerobic colony counts (ACC), coliforms,Escherichia coliand enterococci; 41% of samples yielded ACC above the action level (>1 × 103c.f.u./ml) and 4·5% contained actionable levels (>1 c.f.u./100 ml) of faecal indicator bacteria. Eight hundred and three samples from 360 NPMVs were cultured specifically forLegionellaand 58% of vessels proved positive for these organisms with 27% of samples showing levels greater than the UK upper action limit of 1 × 103c.f.u./l. Cabin showers (49%) and hospital shower (45%) were frequently positive. A subset of 106 samples was analysed by quantitative polymerase chain reaction forLegionellaand identified a further 11Legionella-positive NPMVs, returning a negative predictive value of 100%. There was no correlation between NPMV age or size and any microbial parameters (P> 0·05).Legionella pneumophilaserogroup 1 was isolated from 46% of NPMVs and sequence-based typing of 17 isolates revealed four sequence types (STs) previously associated with human disease. These data raise significant concerns regarding the management of microbial andLegionellarisks on board NPMVs and suggest that better guidance and compliance are required to improve control.