Graduation Year


Document Type




Degree Name

MS in Public Health (M.S.P.H.)

Degree Granting Department

Public Health

Major Professor

Rene R. Salazar, Ph.D.

Committee Member

Steven P. Mlynarek, Ph.D.

Committee Member

John Smyth, Ph.D.


Industrial Hygiene, Bacteria, Legionella, Cooling Towers, Biocides


After the notorious outbreak and discovery of Legionella bacteria in 1976, the waterborne pathogen was added to the list of disease-causing agents associated with the built environment. Legionella pneumophila was discovered when it was identified as the agent that caused 34 deaths and an outbreak of pneumonia-like symptoms in several attendees of the 1976 American Legion Convention held in Philadelphia (OSHA, 2017).

Recently published data from the year 2015 reported more than 6,000 Legionnaires’ cases identified in the United States (CDC, 2016). This is a concerning number given that one in every ten infected persons will die of the disease. It is believed that case numbers are likely under-reported, given that Legionnaires’ disease is very difficult to diagnose.

Legionella species live naturally in bodies of water, including lakes and rivers. Legionnaires’ disease has been associated with the introduction of Legionella into manmade water systems. The presence of Legionella has been reported in cooling towers, domestic hot-water systems, humidifiers, decorative fountains, grocery spray misters, spas, whirlpools, and dental water lines, among other systems housing stagnant water (CDC, OSHA, 2017). From an occupational exposure standpoint, cooling towers are considered the most concerning source of Legionella pneumophila exposures, based on data from previous cases (Principe et al., 2017).

The purpose of this research was to measure the effectiveness of biocide substitution and maintenance management in evaporative condensers. Such condensers were previously identified as having high counts of Legionella pneumophila in the water and/or on surfaces. The study sites were in the states of Florida and Georgia. Initial water testing for Legionella was carried out between July and August of 2016. Results from 2016 showed high counts of colony forming units (CFU) per millimeter (mL) at baseline assessment. An intervention of biocide substitution and enhanced management planning was recommended to lower or eliminate L. pneumophila from the water basins of the evaporative condensers. Follow-up results of water sampling conducted between July and August 2017 showed reduction of CFU counts after the intervention plan had been implemented for an entire year.