Molecular epidemiology of an outbreak of Legionnaires' disease associated with a cooling tower in Genova-Sestri Ponente, Italy

Abstract

Fatty acid profile analysis, monoclonal antibody (MAb) subtyping, pulsed-field gel electrophoresis (PFGE), arbitrarily primed polymerase chain reaction (AP-PCR), and ribotyping were used to compare clinical and environmental Legionella pneumophila serogroup 1 isolates from an outbreak of Legionnaires' disease presumptively associated with cooling towers. According to the Oxford subtyping scheme, the MAb subtype of patients' isolates and of two strains originating from a cooling tower was Pontiac, whereas the other isolates were subtype Olda. The strains showed no intrinsic strain-to-strain difference in fatty acid profiles, and ribotyping and length polymorphism of the 16S-23S rDNA intervening regions failed to reveal any differences between the isolates. Conversely, PFGE and AP-PCR appeared to be more discriminatory, as the same genomic profile was found for the clinical and some environmental strains. Meteorologic and epidemiological data and the results of molecular analysis of the Legionella pneumophila serogroup 1 isolates support the hypothesis that the infection was transmitted from one of the cooling towers to the indoor environment of the same building, to homes in proximity that had open windows, and to the streets. In fact, the outbreak diminished and later ended after a part in the tower was replaced. This investigation demonstrates the utility of combined molecular methods (i.e., phenotypic and genomic typing) in comparing epidemiologically linked clinical and environmental isolates. Finally, the outbreak confirms the risk of Legionnaires' disease posed by cooling towers, mainly when atmospheric thermal and humidity inversions occur. This finding emphasizes the need to determine whether the source of infection is in the living or working environment or somewhere else.

Regrowth of Potential Opportunistic Pathogens and Algae in Reclaimed-Water Distribution Systems

“…The presence of L. pneumophila and Mycobacterium spp. can pose a hazard, particularly when the water is used for irrigation of lawns with sprinklers as the aerosols generated can expose the general public to these pathogens (1,9,36). Inhalation of airborne droplets or drop nuclei that contain Legionella spp.…”

Current and Emerging Legionella Diagnostics for Laboratory and Outbreak Investigations

“…1), such as fountains (84,85,(172)(173)(174)(175)(176), building water systems (75,79,(177)(178)(179)(180)(181)(182)(183)(184), cooling towers (185)(186)(187)(188)(189)(190)(191)(192)(193), and whirlpool spas (194)(195)(196)(197)(198), among others. U.S. surveillance data from 2001 to 2010 have consistently included Legionella as one of the leading causes of drinking waterassociated outbreaks, accounting for 58% of cases in 2010 (199).…”

“…As a standard practice, when possible, the CDC collects both 1-liter bulk water and biofilm swabs in sterile plastic containers from interior locations distal to incoming water, such as shower heads, faucets, hot water heaters, misters, decorative fountains, and spas, and from more central or proximal sites, such as incoming municipal or well water mains and hot recirculation supply lines. Air-conditioning cooling towers, which are historically associated with Legionella contamination (81,245,(515)(516)(517)(518) and LD outbreaks in the United States (187, 519-521) and internationally (186,190,521,522), can support heavy bacterial growth, and all locations within the study zone are routinely sampled. At the time of collection, water is assessed for temperature, pH, and residual disinfectant (e.g., chlorine or bromine) before chemical neutralization with sodium thiosulfate.…”

Persistence of chlorine-sensitiveLegionella pneumophilain hyperchlorinated installations

“…Although most cases of LD are sporadic (PHLS 2000), there have been outbreaks involving a wide variety of facilities, including cooling towers (Keller et al. 1996; Castellani‐Pastoris et al. 1997; García‐Fulgueiras et al.…”