Mysteriously Rapid Rise in Legionnaires’ Disease Incidence Traced to Declining Sulfur Dioxide

FANGQUN YU, Arshad Nair, Ursula Lauper, Gan Luo, Jason Herb, Matthew Morse, Braden Savage, Martin Zartarian, Shao Lin, The State University of New York at Albany

     Abstract Number: 364
     Working Group: Aerosol Science of Infectious Diseases: Lessons and Open Questions on Models, Transmission and Mitigation

Abstract
Legionnaires’ disease (LD) is a severe form of pneumonia with a hospitalization rate of ~ 95% and a fatality rate of ~ 10–25% that is caused by multiple bacterial species of the Legionella genus. Legionella are found naturally in freshwater such as lakes and streams. The bacteria can become a health concern when they grow and spread in built water systems like cooling towers (CTs), hot tubs, decorative fountains, hot water tanks, showerheads, and sink faucets. Infection occurs when aerosolized Legionella are inhaled, or contaminated water is aspirated and bacteria enter the lungs. A recent dramatic increase in LD incidence has been observed globally, with a nine-fold increase in the US from 2000 to 2018, and with a disproportionately higher burden for socioeconomically vulnerable subgroups. Despite the focus of decades of research since the infamous 1976 outbreak, substantial knowledge gaps remain with regard to the source of exposure and the reason(s) for the dramatic increase in LD incidence. Here, we analyze reported LD case data along with air quality, meteorology, and cooling tower data. We rule out factors indicated in the literature to contribute to its long-term increases and identify a hitherto unexplored explanatory factor. We provide an epidemiological demonstration that the occurrence of LD is linked with exposure to cooling towers. Our results suggest that declining sulfur dioxide air pollution, which has many well-established health benefits, results in reduced acidity of aerosols emitted from cooling towers, which may prolong the survival duration of the Legionella in contaminated cooling tower droplets and contribute to the increase in LD incidence. Mechanistically associating decreasing aerosol acidity with this respiratory disease has implications for better understanding its transmission, predicting future risks, and informed design of preventive and interventional strategies that consider the complex impacts of continued sulfur dioxide changes.