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An outbreak of Legionella pneumophila suspected to be associated with spa pools on display at a retail store in New Zealand.

AIM
To investigate and characterise a cluster of six cases of severe pneumonia in the Wellington region notified to Regional Public Health in November 2003. And to describe the public health response to an identified subgroup of Legionella infections.


METHODS
The case definition was "a person admitted to Wellington or Hutt Hospital between 29 October 2003 and 9 November 2003 with severe pneumonia". The cluster was initially investigated by interviewing patients to obtain histories of activities and exposures, and by reviewing medical notes. Medical teams sent further clinical specimens for testing (sputum for polymerase chain reaction [PCR], convalescent Legionella serology, and urine for Legionella antigen testing). Further investigation of Legionella pneumophila cases involved obtaining detailed exposure histories, environmental investigations at the suspect source of infection, and taking water and biofilm swabs for Legionella detection and serotyping.


RESULTS
Three cases from the cluster were confirmed as, or compatible with, Legionella pneumophila serogroup 2. With the other three cases there was evidence of infection with L. longbeachae (two cases) or respiratory syncytial virus (one case). Exposure histories for the L. pneumophila cases revealed that the three cases had visited a Lower Hutt retail outlet with operating spa pools on display. Legionella pneumophila serogroup 1 was cultured from one of three pools. All pools were positive for Legionella on direct fluorescent antibody testing.


CONCLUSIONS
Although unproven, the display spa pools were considered to be the most likely source of Legionella infection in the three cases that had visited the retail outlet. Although Legionella isolated from the pools was a different serogroup from that identified in two cases, the pools were considered to be the most likely source of infection in view of inadequate chlorination of the waters. Public health intervention to address the immediate and longer-term health risks from the pools is described. This is the second outbreak of Legionella pneumophila linked to operating display spa pools in New Zealand and it appears to be the fourth recorded outbreak of Legionnaires' disease associated with operating spa pools on display.