Overview of the Draft document: 

“Technologies for Legionella Control:

Scientific Literature Review”

November 9, 2015

César Cordero

U.S. Environmental Protection Agency

OW/Office of Ground Water and Drinking Water

Standards and Risk Management Division
Legionella: A Major Public Health Problem

• Legionellosis1 is a major health concern associated 

with drinking water 

• CDC estimates 8,000 – 18,000 legionellosis 

hospitalizations occur in the U.S. annually, with up to 

a 30% fatality rate

• Hospitalization costs for Legionnaires’ disease are 

estimated at $433 million/year

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1 Legionellosis is a form of atypical pneumonia caused by Legionella bacterial infection. The disease 

can occur in two forms: a pneumonia-like infection (Legionnaires' Disease) or a flu-like illness 

(Pontiac fever).
• Legionella bacteria are found naturally in the 

environment worldwide, usually in aquatic 

environments

• Legionella colonizes biofilms2 in premise plumbing

• Infection occurs primarily through inhalation or 

aspiration

– Showerheads, faucets and hot tubs 

– Mist machines, decorative fountains and cooling towers

– Respiratory therapy devices and humidifiers

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2 Biofilms form when microbes stick to surfaces in aqueous environments and excrete a slimy, gluelike substance that can anchor them to all kinds of material. 

Legionella: A Major Public Health Problem
Legionella: A Major Public Health Problem

• Waterborne disease outbreaks (2009-2012, 

reported by CDC)

– 40 of 65 (62%) of the waterborne disease 

outbreaks caused by Legionella

– 32 of 40 (80%) Legionella outbreaks caused by 

environmental conditions within water systems of 

buildings

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Applicable Drinking Water Regulation

• Surface Water Treatment Rule (SWTR) - 1989: 

– Applies to surface water (SW) and ground water 

under direct influence of SW

– MCLGs of zero for Giardia, viruses and Legionella

– The SWTR presumes that compliance with the 

treatment technique (TT) requirements3 will control 

for Legionella in utilities

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3 TT requirements: Remove/inactivate Giardia lamblia and viruses before distribution; maintain a 

detectable residual disinfectant level in the distribution system.
Premise Plumbing Issues

• Premise plumbing refers to the pipes after the 

service connection line all the way to the tap, 

such as those in:

– Hospitals, schools, businesses, and private 

buildings

• Premise plumbing conditions can lead to 

Legionella proliferation (e.g. water heating, 

long residence time, low disinfectant residual 

areas)

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Legionella Document Overview

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• EPA worked with a multi-agency team to develop this draft technical 

document that compiles peer reviewed literature on technologies that 

control for Legionella in premise plumbing

• The multi-agency team participated in the data compilation, write up 

and review of the draft document

– EPA (Regions, OGC, OPP & ORD), CDC, ASDWA, state representatives

• The document summarizes literature for each technology

– Effectiveness against Legionella

– Potential water quality issues

– Operational requirements

• The document does not recommend any particular technology nor 

the addition/installation of treatment

• The document provides an overview of the regulatory context
• Chlorine 

– Results of laboratory and pilot scale studies showed 

effectiveness but at wide range of dose and water quality 

conditions 

– Residual maintenance is important

– Efficacy increases with increased temperature

– Biofilms and inclusion of Legionella in amoeba shield 

organisms from chlorine

– Potential water quality issues include disinfection byproducts 

(Trihalomethane (THM) and haloacetic acid (HAA)), taste and 

odors and corrosion

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Control Technologies
• Monochloramine

– Laboratory studies showed wide range of 

inactivation under varying water quality conditions

–Efficacy increases with increased temperature

–Several studies concluded chloramine is more 

effective at penetration of biofilms than chlorine

–Potential water quality issues include disinfection 

byproduct formation (nitrosamines), nitrification, and 

corrosion

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Control Technologies (Cont.)
• Chlorine Dioxide

– Laboratory and pilot scale testing showed effectiveness at low 

doses (<1 mg/l)

– Effective against Legionella shielded in amoebae and at 

penetrating biofilms

– Literature reports successful applications of chlorine dioxide 

disinfection systems in hospitals

– Efficacy increased with increased water temperature

– Potential water quality issues include formation of chlorite and 

chlorate, taste and odors, and corrosion

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Control Technologies (Cont.)
• Copper-Silver Ionization (CSI)

– Laboratory studies indicate that copper ions (at 0.4 mg/L) and silver 

ions (at 0.04 mg/L) can reduce cultivability of Legionella

– Literature reports successful applications in building water systems

– Biofilms and inclusion of Legionella in amoeba shield the organism 

from CSI

– Legionella strains appear to develop resistance to copper and silver

– Potential water quality issues include high copper concentrations, 

and corrosion

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Control Technologies (Cont.)
• UV Disinfection

– Shown to be effective at decreasing and in some cases, 

eliminating Legionella from building water systems at low 

doses (40 mJ/cm2)

– Only effective on water flowing through the reactor; when 

Legionella is already present in building water systems, 

supplemental treatment is required

– Some UV reactors may not be tolerant of high temperatures 

(e.g. > 35oC/ 95 oF) or certain chemical disinfectants

– Iron, manganese, calcium and magnesium may affect the 

quartz lamp sleeves decreasing UV output

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Control Technologies (Cont.)
• Ozone

‒ Laboratory studies showed wide range of inactivation under 

varying water quality conditions

‒ Decomposes quickly in water thus it is difficult to maintain a 

disinfectant residual 

• Particularly at higher temperatures

• Second form of disinfection may be needed

‒ Effects of biofilms and inclusion of Legionella in amoeba 

from ozone not well characterized

‒ Potential water quality issues include formation of 

disinfection byproducts and corrosion

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Control Technologies (Cont.)
• Emergency Disinfection

– Superheat-and-Flush Disinfection

• Involves raising the hot water temperature to 71-77 oC while flushing each 

outlet for at least 30 minutes

• Has shown to be effective, particularly in hospital outbreak scenarios

• Regrowth is an issue. May not provide long-term control unless combined 

with supplemental disinfection

– Shock Hyperchlorination

• Involves injecting elevated chlorine concentration (20-50 ppm) for a 

specific contact time 

• Success for control of Legionella has been mixed

• Legionella can be protected within Acanthamoeba, which can survive 

chlorine concentrations of 50 ppm 14

Other Control Technologies
• Point-of-Use Filtration

–Effectiveness demonstrated by several case studies

– Dependent on pore size (≤ 0.2μm). 

– Depth filtration, including the use of silverincorporated BAC filtration, not effective

–Filters may clog and failure could lead to release of 

high levels of pathogens. 

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Other Control Technologies (Cont.)
Preventative and Remediation Strategies

• Multi-barrier Approaches (e.g. Water Safety 

Plans, Water Management Plans, Hazard 

Analysis and Critical Control Points 

programs)

–Approaches for protecting building water systems 

from hazards that may occur

– Case studies show effectiveness for controlling 

growth of pathogens in building water systems

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Next Steps 

• Evaluate and revise the document based on 

public input – Nov./Dec. 2015

• Independent external peer review – Jan. 2016

• Publish final document – Spring 2016

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Clarification Questions

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