Our Legionella Research

Special Pathogens Laboratory sets the industry standard for Legionella control through our introduction and evaluation of disinfection technologies. Since the early 1990s, we have tested all major Legionella disinfection technologies used in the field and continue to explore new technologies. Our findings are published in peer-reviewed scientific and medical journals. We recommend a step-wise evaluation to validate the efficacy of disinfection methods for Legionella in water systems Our four-step approach is published in the Experiences of the First 16 Hospitals Using Copper-silver Ionization: Implications for the Evaluation of Other Disinfection Modalities (2003).

Legionella Disinfection Technologies

Following are disinfection technologies shown to effectively reduce the presence of Legionella in water systems:


Monochloramine has been used successfully for municipal water treatment. We conducted the first U.S. study of an onsite monochloramine generation system for Legionella disinfection. The results showed a significant decrease in Legionella percent positivity of the hospital’s hot water system soon after installation. Dr. Stout presented findings at the annual Association of Water Technologies conference in September 2012.

After monitoring the system for a total of 29 months, results showed consistent efficacy and appears in the November issue of Infection Control and Hospital Epidemiology.

Evaluation of a New Monochloramine Generation System for Controlling Legionella in Building Hot Water Systems. Scott Duda, MS; Sheena Kandiah, MD, PhD; Janet E. Stout, PhD; Julianne L. Baron, BS; Mohamed Yassin, MD, PhD; et al.  Infection Control and Hospital Epidemiology; November 2014, Vol. 35, No. 11.

SPL presented two posters on monochloramine in October 2013 at the Eighth International Conference on Legionella in Australia

Monochloramine Disinfection of a Hospital Water System for Preventing Hospital-Acquired Legionnaires’ Disease: Lessons Learned from a 1.5 Year Study presented more data of the first US field study of a monochloramine generating system in a hospital hot water system. The conclusions show monochloramine to be a promising disinfectant for Legionella.

Use of Pyrosequencing to Determine the Effects of Monochloramine Treatment on Legionella and Associated Bacterial Populations in a Hospital Hot Water System is the first US study to assess changes in Legionella and microbial flora due to chloramination in a hospital’s hot water system using next generation sequencing. This study shows a strong reduction in Legionella presence and a lack of many issues with chloramination found in municipal water supplies.

Copper-Silver Ionization

Copper and silver ions are bactericidal against Legionella and other waterborne pathogens. A study by Dr. Janet E. Stout and Dr. Victor L. Yu, published in Infection Control and Hospital Epidemiology, documents that copper-silver ionization significantly reduced Legionella in hot water distribution systems of 16 hospitals, and reduced or eliminated cases of hospital-acquired Legionnaires’ disease.

Experiences of the First 16 Hospitals Using Copper-Silver Ionization for Legionella Control: Implications for the Evaluation of Other Disinfection Modalities. Janet E. Stout, PhD; Victor L. Yu, MD. Infection Control and Hospital Epidemiology; Aug. 2003: Volume 24, No. 8.

Chlorine Dioxide

Our research showed that Legionella can be successfully controlled by chlorine dioxide. The time needed to achieve requisite reduction in percent positivity is site specific and dependent on whether the application point is on the cold water, hot water or a combination.

Prospective study of the safety and efficacy of chlorine dioxide for Legionella control in a hospital water system.  Zhang Z, McCann C, Stout JE, et al.  Infection Control and Hospital Epidemiology. 2007; 28(8).

Point-of-Use Water Filters

Special Pathogens Laboratory and others have shown in independent studies that Point-of-Use (POU) water filters prevent exposure to waterborne pathogens from faucets, showers and ice machines. These pathogens include LegionellaPseudomonas and nontuberculous mycobacterium.

Efficacy of new point-of-use water filter for preventing exposure to Legionella and waterborne bacteria. Sheffer PJ, Stout JE, Wagener MM, Muder RR. Am J Infect Control. 2005 Jun;33(5 Suppl 1):S20-5.

Ultraviolet Light

Research by Special Pathogens Laboratory showed that focal disinfection with UV light could reduce Legionella in a hospital when combined with a systemic disinfection method.

Disinfection of water distribution systems for Legionella. Lin YS, Stout JE, Yu VL, Vidic RD. Semin Respir Infect. 1998 Jun;13(2):147-59. Review.

Product Evaluations

Special Pathogens Laboratory conducts evaluations that detect, treat or control Legionella and other waterborne pathogens, as well as antimicrobial innovations to combat the spread of infection at manufacturers’ requests. We validate the efficacy of disinfection methods for Legionella in water systems using a stepwise evaluation criteria. Our approach is published in the Experiences of the First 16 Hospitals Using Copper-silver Ionization: Implications for the Evaluation of Other Disinfection Modalities (2003).

Point-of-Use Water Filter Field Evaluation

Point-of-use (POU) water filters limit exposure to Legionella and other waterborne pathogens. However, these filters are costly due to a short life cycle and membrane clogging. Recently, Pall Medical released a new generation QPoint filter with a 62-day use duration with less propensity for clogging. SPL investigated the manufacturer’s claims by conducting a field evaluation at a cancer center in northwestern Pennsylvania. The 17-week study showed the filter was successful on both counts and could provide a more convenient and cost-effective solution for infection prevention.

Field evaluation of a new point-of-use faucet filter for preventing exposure to Legionella and other waterborne pathogens in health care facilities.  (J Baron, et al. American Journal of Infection Control. 2014 November, 42 (11):1193-1196.

Nonchemical Water Treatment Devices (ASHRAE-Funded Study)

The first study of the efficacy of nonchemical treatment devices for controlling microbiological activity (planktonic and sessile) within a pilot scale model cooling tower.

Biological control in cooling water systems using nonchemical treatment devices. Scott Duda, Janet E. Stout & Radisav Vidic (2011) HVAC&R Research, 17:5, 872-89.

QPoint Filter

Legionella, Pseudomonas aeruginosa, and other opportunistic waterborne pathogens can persist in water distribution systems despite municipal chlorination and secondary disinfection. These organisms can cause healthcare-acquired infections in immunocompromised patients. Point-of-use (POU) water filtration can limit exposure to these organisms in high-risk areas of hospitals; however short (31 day) maximum lifetime and membrane clogging can limit their use. SPL collaborated with a Pennsylvania healthcare facility to perform a field evaluation of a new point-of-use faucet filter that was developed to address these limitations. The results were shared at a poster session at APIC 2014 in June.

Evaluation of a New Point-of-Use Faucet Filter for Preventing Legionella and Total Bacteria. Download poster.

Point-of-Use Water Filters

Efficacy of new point-of-use filter for preventing exposure to Legionella and waterborne bacteria. Sheffer PJ, Stout JE, Wagener MM, Muder RR.  American Journal of Infection Control. 2005; 33(5) Suppl. 1: S20-S25.

Real-Time Quantitative PCR

SPL researchers evaluated a novel PCR method for the detection of Legionella in water using the GeneDisc system (Pall Corporation).

Poster:  A Rapid Method for the Detection of the Nosocomial Waterborne Pathogens Legionella spp. and Pseudomonas aeruginosa by Real-time Quantitative PCR: A Comparison with Standard Culture. Sue M. Mietzner, Pratima Adhikari, Janet E. Stout, Victor L. Yu (Special Pathogens Laboratory and University of Pittsburgh)

PDISani-Hands® ALC Antimicrobial Alcohol Gel Hand Wipes

Alcohol-based wipes significantly more effective than rubs in reducing bacteria; findings could impact hospital-acquired infections. SaniPDI Inc. is the global leader in pre-moistened wipes for the healthcare industry. SPL researchers evaluated the efficacy of the PDI Sani-Hands® ALC Antimicrobial Alcohol Gel Hand Wipes vs. hand gel and soap.

Special Pathogens Laboratory’s study measured the effectiveness of this ethanol wipe against an ethanol rub (Purell®) in eliminating bacteria. Our study shows that wipes-towelettes saturated with alcohol are more effective than popular alcohol-based hand rubs in reducing bacteria from hands. Specifically, PDI Sani-Hands® was significantly more effective than the rub in reducing the number of viable bacteria on hands.

Revisiting the hand wipe versus gel rub debate: Is a higher-ethanol content hand wipe more effective than an ethanol gel rub?  D’Antonio NN, Rihs JD, & Stout JE, Yu VL. Am J Infect Control 2010;38 (9):671-758


Antimicrobial Polymer in Keyboard Covers Significantly Reduces Microbial Contamination

Biosafe, Inc. introduced a novel antimicrobial polymer, BIOSAFE HM4100, that can be incorporated into a variety of materials, including the polyurethane used to make keyboard covers and other plastics.

SPL performed a study to determine whether plastic keyboard covers compounded with HM4100 effectively minimizes the survival of bacterial species commonly present on environmental surfaces in the healthcare setting. The Biosafe coating demonstrated efficacy in reducing viability of methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, E. coli, and vancomycin-resistant Enterococcus faecalis (VREF).

Computer Keyboard Covers Impregnated with a Novel Antimicrobial Polymer Significantly Reduce Microbial Contamination. D’Antonio N, Rihs JD, Tosiano M, Stout JE. Association for Professionals in Infection Control and Epidemiology, Inc., Fort Lauderdale, FL, June 2009. 

University-Affiliated Research

Special Pathogens Laboratory advances independent research to evaluate new methodologies, products, and approaches to diagnosis for the treatment and prevention of Legionnaires’ disease and other infectious diseases through an academic affiliation with the University of Pittsburgh.

Since 1995, Special Pathogens Laboratory researchers have mentored students from the fields of medicine, microbiology and engineering. Many of their students have presented research at national meetings and have been published in peer-reviewed journals, while others have become leaders in their respective fields with major research contributions. Following is selected research:

Shift in Microbial Ecology in Hospital Hot Water System Treated with Monochloramine

With the increase of Legionnaires’ disease and the passage of Legionella management standards and other guidelines, many facilities are considering applying secondary disinfection to water distribution systems. However, little is known about how these chemicals impact the microbial ecology. Using next generation sequencing methods, SPL evaluated samples from a hospital’s hot water system treated with onsite monochloramine. The results showed an immediate shift in the microbial population following treatment. Next generation sequencing, along with traditional culture, showed changes in Legionella, including rebound during a period of ineffective treatment. To understand the impact of different disinfection technologies on water systems more studies on the microbiome of the built environment, an emerging field or study, are needed.

Shift in the Microbial Ecology of a Hospital Hot Water System following the Introduction of an On-Site Monochloramine Disinfection System (Julianne L. Baron, Amit Vikram, Scott Duda, Janet E. Stout, Kyle Bibby. PLOS ONE Journal. July 2014.Vol 9 Issue 7.) 

Non-chemical Treatment Devices Study

The Non-chemical Treatment Device study was conducted by Dr. Stout, lead investigator Radisav Vidic, chair and William Kepler Whiteford Professor of civil and environmental engineering, and then-Pitt civil and environmental engineering graduate student Scott Duda. The specific objective of this investigation was to provide a controlled, independent, and scientific evaluation of several classes of non-chemical treatment devices (NCDs) for controlling biological activity in a model cooling tower system. The two-year study was funded by American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE).

Microbial growth in cooling water systems causes corrosion, decreases energy efficiency, and has the potential to cause human infection. Control of microbial growth in these systems is typically achieved with the use of chemical biocides. Recently, non-chemical water treatment methods have seen increased use as an alternative. However, few objective studies with an untreated system as a reference are available to verify the efficacy of these devices to control microbial growth in cooling towers.

Five NCDs were evaluated for efficacy in reducing planktonic (bulk water) and sessile (biofilm) microbial populations within a pilot-scale cooling system. The devices included magnetic, pulsed electric field, electrostatic, ultrasonic, and hydrodynamic cavitation:

  • Magnetic Device (MD): RT-750-K Superior Water Conditioner®, Magnatech Corp, Fort Wayne, Ind.
  • Pulsed Electric Field Device (PEFD): Dolphin Series 3000, Clearwater Systems Corp., Essex, CT
  • Electrostatic Device (ED): FluidTron®, ElectroStatic Technologies, Inc., Kansas City, Kan.
  • Ultrasonic Device (UD): Sonoxide® B02, Ashland Water Technologies, Wilmington, Del.
  • Hydrodynamic Cavitation Device (HCD): VRTX-10, VRTX Technologies, Schertz, Texas
  • Biological Control in Cooling Water Systems Using Non-Chemical Treatment Devices, ASHRAE 1361RP