Title: Long-term Efficacy of Monochloramine Against Legionella and Waterborne Pathogens in A Large Healthcare Facility
Learner Objectives:
To evaluate the long-term efficacy of monochloramine for controlling Legionella and other waterborne pathogens and assess water quality changes.
Content/Topic Outline:
Presenter:
Janet E. Stout, PhD
Review intial evaluation results and conclusions on the impact of long-term monochloramine, including the effectiveness against Legionella.
David Pierre
Review results and data from the three follow-up sampling events.
Presentation Description:
We have performed field evaluations of all currently available disinfection methods for controlling Legionella in building potable water systems, including chlorine dioxide, chlorination, copper-silver ionization, and thermal eradication. In 2014 we published the first prospective evaluation of monochloramine efficacy installed on a U.S. hospital hot water system. That study presented results from a 2-year post disinfection period from 2011 to 2013. The objective of this study was to continue the evaluation and determine the long-term efficacy of monochloramine for controlling Legionella and other waterborne pathogens and assess water quality changes.
The study was conducted at a 500 bed hospital Pittsburgh, PA, the same site as our previous evaluation. The monochloramine system was operated and monitored by the water treatment professional with oversight by the water safety team.
Three sampling events were performed: September 2020, March 2021 and October 2021. Twenty-nine samples were collected as part of the initial follow-up evaluation in September. Legionella, Heterotrophic Plate Count bacteria (HPC), Pseudomonas, Acinetobacter, Stenotrophomonas, non-tuberculous mycobacteria (NTM), and nitrifying bacteria were monitored. Chlorine (total and free), monochloramine, and metals were also monitored. Twenty samples were collected in March and October of 2021.
September 2020 represented 9 years post installation and test results showed 0% (0/29) of samples positive for Legionella. Results for other waterborne pathogens showed the following sample positivity: 7% Pseudomonas, 0% Acinetobacter, 0% Stenotrophomonas, 48% Mycobacteria, and 0% nitrifying bacteria. Monochloramine residuals in the distal sites were lower than desired during this sampling event (Average: 1.15 ppm, Range 0.00 – 1.54 ppm). Consistent with previous results, there was no evidence of lead leaching. The equipment was serviced and adjusted to increase the monochloramine output target (2.5-3.0 ppm). Sampling in March and October 2021 was performed to evaluate the effect of the adjustment on NTM positivity.
Sampling results in March 2021 showed Mycobacteria positivity remained high (65% positivity). Average monochloramine at the distal outlets had increased to2.05 ppm (range: 0.38 ppm – 2.54 ppm).
The final sampling event was in October 2021 and consisted of Legionella, HPC, mycobacteria, and metals. No Legionella was detected (0% positivity), however 55% of samples tested positive for Mycobacteria. Average monochloramine concentration was 2.84 ppm (range: 0.78 ppm – 3.24 ppm); higher than the previous two sampling events.
The results from this follow up study demonstrated that monochloramine applied to the hot water system of this hospital was effective for long-term control and management of Legionella. Among the other waterborne pathogens tested, only non-tuberculous mycobacteria (NTM) positivity remained unchanged or increased, an outcome not unexpected due to its intrinsic resistance to disinfectants including chlorine. Monitoring of metals indicates that the system can provide Legionella control while meeting water quality standards with low corrosion concerns. Facilities utilizing and maintaining a monochloramine system with action limits at 2.0 ppm -3.0 ppm should expect to see similar results.
Presenter Bio:
Janet E. Stout, PhD
Dr. Janet E. Stout is president and director of Special Pathogens Laboratory, and research associate professor at the University of Pittsburgh Swanson School of Engineering in the Department of Civil and Environmental Engineering. An infectious disease microbiologist, Dr. Stout is recognized worldwide for seminal discoveries and pioneering research in Legionella. Her expertise includes prevention and control strategies for Legionnaires’ disease in building water systems. Dr. Stout’s more than 30 years of research is published in peer-reviewed medical and scientific journals. She has also authored textbook chapters on Legionella and Legionnaires’ disease, including the Legionella chapter in the APIC Text. An advocate for prevention, Dr. Stout assisted in developing the first Legionella prevention guideline (1993) in the United States, which continues to serve as a model for national and global health agencies and organizations. Additionally, she serves on the ASHRAE Legionella standard committee for Legionella Guideline 12 and the SPC 188 committee for ANSI/ASHRAE Standard 188-2015 Legionellosis: Risk Management for Building Water and is the first ASSE certified instructor for the certification training to the ASSE Standard 12080 Professional Qualifcations Standard for Legionella Water Management Specialists.
Dave Pierre
David Pierre is vice president of SPL Consulting Services at Special Pathogens Laboratory. An expert in New York City and State regulations for Legionella risk management and ANSI/ASHRAE Standard 188, Pierre has overseen the development of more than 200 water safety and management plans and risk assessments for healthcare, hospitality, commercial, and industrial facilities. Pierre’s background in microbiology complements his in-depth understanding of the physical conditions for Legionella and waterborne pathogens in premise plumbing and cooling towers.