Abstract
At the U.S. Department of Energy’s Savannah River Site (SRS) in Aiken, SC, cooling tower water is routinely monitored for Legionella pneumophila concentrations using a direct fluorescent antibody (DFA) technique. Historically, 25–30 operating SRS cooling towers have varying concentrations of Legionella in all seasons of the year, with patterns that are unpredictable. Legionellosis, or Legionnaires’ disease (LD), is a pneumonia caused by Legionella bacteria that thrive both in man-made water distribution systems and natural surface waters including lakes, streams, and wet soil. Legionnaires’ disease is typically contracted by inhaling L. pneumophila, most often in aerosolized mists that contain the bacteria. At the SRS, L. pneumophila is typically found in cooling towers ranging from non-detectable up to 108 cells/L in cooling tower water systems. Extreme weather conditions contributed to elevations in L. pneumophila to 107–108 cells/L in SRS cooling tower water systems in July–August 2017. L. pneumophila concentrations in Cooling Tower 785-A/2A located in SRS A-Area, stayed in the 108 cells/L range despite biocide addition. During this time, other SRS cooling towers did not demonstrate this L. pneumophila increase. No significant difference was observed in the mean L. pneumophila mean concentrations for the towers (p < 0.05). There was a significant variance observed in the 285-2A/A Tower L. pneumophila results (p < 0.05). Looking to see if we could find “effects” led to model development by analyzing 13 months of water chemistry and microbial data for the main factors influencing the L. pneumophila concentrations in five cooling towers for this year. It indicated chlorine and dissolved oxygen had a significant impact (p < 0.0002) on cooling tower 785A/2A. Thus, while the variation in the log count data for the A-area tower is statistically greater than that of the other four towers, the average of the log count data for the A-Area tower was in line with that of the other towers. It was also observed that the location of 785A/2A and basin resulted in more debris entering the system during storm events. Our results suggest that future analyses should evaluate the impact of environmental conditions and cooling tower design on L. pneumophila water concentrations and human health.
Highlights
Legionella pneumophila, the cause of Legionnaires’ disease (LD), is a Gram-negative bacterium ubiquitous in man-made and natural aquatic environments, where it survives in biofilms (Wery et al, 2008)
While no cases of legionellosis were documented in this case at the SRS during this time of extreme weather, conditions including summer weather, high rainfall, increased humidity, and cloudy conditions were conducive for Legionella growth conditions
The factor of temperature and high precipitation have been linked with higher incidences of Legionellosis (Han, 2019)
Summary
Legionella pneumophila, the cause of Legionnaires’ disease (LD), is a Gram-negative bacterium ubiquitous in man-made and natural aquatic environments, where it survives in biofilms (Wery et al, 2008). Legionellosis, or Legionnaires’ disease, is a pneumonia caused by Legionella bacteria that thrive both in man-made water distribution systems and natural surface waters including lakes, streams, and wet soil (Fliermans, 1985). There are currently over 60 known Legionella species and 71 serogroups of L. pneumophila, with many of these serogroups implicated in human disease (Me rault et al, 2011; Katsiaflaka et al, 2016; Miyashita et al, 2020). Other Legionella types have been implicated in disease, most often Legionella pneumophila serogroups 4 and 6, as well as other serogroups (Buchbinder et al, 2002; Fields et al, 2002; Paranjape et al, 2020), and coinfections with several Legionella species due to immunodeficiencies (Matsui et al, 2010)
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