Centers for Disease Control

and Prevention

National Institute for Occupational 

Safety and Health

Preventing Occupational Exposure

to Legionella

Summary

The National Institute for Occupational Safety and Health (NIOSH) 

has conducted Health Hazard Evaluations (HHEs) in workplaces with reported cases of Legionnaires’ disease among employees. After each of 

these evaluations, NIOSH made recommendations to employers to prevent conditions that lead to Legionella growth and spread in workplaces. 

Exposure

Legionnaires’ disease is a form of pneumonia that can be severe. It is caused by 

breathing in or aspirating small water 

droplets containing a pathogenic type 

of Legionella bacteria [CDC 2018b]. 

Legionella can also cause a less serious infection called Pontiac fever that 

has symptoms similar to a mild case of 

the flu. Historically, most outbreaks of 

Legionnaires’ disease have occured in 

buildings with large complex water systems. Workplaces that have been associated with outbreaks include hotels, 

hospitals, nursing homes, plastic injection molding manufacturers, and automobile manufacturers [CDC 2016a]. 

In recent years, community-wide outbreaks caused by construction-related 

disturbance to drinking water distribution lines or cooling towers have also 

been observed.

Legionella is usually not transmitted from person to person [Correia et 

al. 2016]. Risk factors for developing 

Legionnaires’ disease include having 

chronic lung disease, a weakened immune system, liver or kidney failure, 

cancer, or diabetes; older age; and cigarette smoking [CDC 2016b,c; 2017a; 

NAS 2019].

Legionella grows in water sources when 

the following conditions occur [CDC 

2016a,b, 2017a]: 

 A water disinfection system fails:

— Water not flowing.

— Disinfectant levels are not 

maintained.

— Presence or introduction of 

“deadlegs” into new construction or allowing plumbing to 

remain stagnant during construction or renovations of a 

building.

 Unmanaged external changes to the 

building, such as nearby construction, affect potable water quality.

 Water temperatures that are not hot 

or cold enough to prevent growth of 

Legionella. 

In the workplace, common sources of water that may contain Legionella include the following [CDC 2016b,c, 

2017a; OSHA 2018]:

 Cooling towers for air-conditioning systems, evaporative condensers, and fluid coolers that use evaporation to reject heat. These include 

many industrial processes that use 

water to remove excess heat.

 Humidifiers, decorative fountains, 

misters, tubs, therapeutic spas, garden hoses, and other devices that 

create a water spray and use water at 

temperatures favorable to Legionella 

growth. These systems may not have 

adequate disinfectant to control Legionella growth. 

 Safety equipment including fire 

sprinkler systems, eye wash stations, 

and safety showers 

 Hot water systems (including faucets 

and showers), especially those with 

thermal mixing valves and electronic eye actuators

 Specialized medical devices (e.g., respiratory therapy equipment, hydrotherapy tubs, and heater-cooler units)
2 

 Recirculated process water, including vehicle water tanks 

used for street cleaning and dust control [Valero et al. 

2017] and asphalt paving machines [Coscollá et al. 2010]

 Carbon filters to improve the odor and taste of drinking 

water fountains and ice machines 

Guidelines to Control Exposure

To help building owners and managers reduce the risk of Legionella growth and transmission, guidelines and standards 

have been developed by a number of agencies and professional groups.

CDC

To help building owners and managers reduce the risk of 

Legionella growth and transmission, the Centers for Disease Control and Prevention (CDC) has developed a toolkit that provides step-by-step guidance on how to set up a 

water management program [CDC 2018c]. The CDC toolkit explains the information provided in the ANSI/ASHRAE 

Standard 188-2018 Legionellosis: Risk Management for Building Water Systems [ASHRAE 2018]. 

OSHA

The Occupational Safety and Health Administration (OSHA) 

has developed guidance dealing with potential exposures to 

Legionella [OSHA 2018]. The guidance provides information about the disease, how to identify likely environmental sources of Legionella, and methods to reduce exposure. 

EPA

The Environmental Protection Agency (EPA) has developed 

a review of the commonly used disinfection strategies for Legionella control in premise plumbing systems [EPA 2016]. 

Disinfectants must comply with the EPA Federal Insecticide, 

Fungicide, and Rodenticide Act (FIFRA). 

AIHA

The American Industrial Hygiene Association (AIHA) published guidelines on the Recognition, Assessment and Control 

of Legionella in Building Water Systems [AIHA 2015]. These 

guidelines provide a framework for employers to carry out 

risk assessment for Legionella sources and to perform environmental sampling as part of routine or investigative assessments.

Case Study

This case study emphasizes Legionella exposures in an industrial setting. NIOSH visited an automobile and scrap metal 

shredding facility after four employees developed Legionnaires’ disease. Automobile and scrap metal shredding is 

done in a large shredding machine (Figure 1) and generates 

dusts, mists, and vapors. The shredding chamber inside the 

machine is cooled and lubricated using municipal water. The 

four employees with Legionnaires’ disease performed shoveling and picking activities. Picking involves manually removing copper and other materials from the shredder conveyor belt. 

NIOSH identified Legionella on a sterile swab sample taken 

from a wet conveyor belt that exited the shredder, in water 

dripping from the belt, and from a sterile swab sample taken 

on a wet conveyor belt inside the picking shed. In addition, 

clouds of water vapor were observed above the conveyor 

belt. NIOSH investigators also observed large quantities of 

standing water throughout the facility grounds. Legionella 

was identified in several puddles of water. Employees stood 

and shoveled in and around water, vehicles drove through 

water, and front-end loaders picked up and set down material in and around standing water, creating splashes. No employees wore respirators.

NIOSH investigators recommended that employers sanitize 

equipment, improve drainage, and implement a respiratory protection program for employees who do maintenance 

work and are exposed to water spray. NIOSH also recommended that employees avoid shoveling during shredding 

operations, and avoid smoking or eating in the plant production areas. 

Figure 1. Water vapor emitted from shredding machine.

During a return visit 4 months later, NIOSH investigators observed that the facility grounds had been cleared of 

built-up dirt, improving drainage and revealing a previously 

blocked drain. A new, larger shredder that required only half 

the previous water flow had been installed. The plant manager reported that the picking room had been cleaned and sanitized, but not the rest of the facility. Some puddles of water 

Photo by NIOSH
3

still existed, and Legionella was again detected in water samples taken from multiple puddles. Legionella was not detected in swab samples taken from the conveyor system. During 

this visit, employees wore N-95 respirators provided by the 

facility; but none had been fit-tested and some were wearing 

their respirators incorrectly. 

NIOSH recommended that the ground drainage be improved to remove the remaining standing water, that the rest 

of the facility be cleaned and sanitized, and that employees 

wear respirators correctly and be fit-tested [NIOSH 2012]. 

Recommendations

Employees, employers, and building managers should take 

the following steps to reduce the risk of Legionella growth 

and transmission in the workplace [NIOSH 2012, 2016a].

Employees

Report signs or symptoms that might be pneumonia to your 

personal healthcare provider and (as instructed by your employer) to a designated individual at your workplace. If you 

have symptoms and work around aerosolized water, special tests are needed to determine whether you have Legionnaires’ disease.

Healthcare Providers

Healthcare providers can ask employees with pneumonia 

symptoms whether they work around water that can be easily aerosolized and what jobs they do to get more information 

about possible exposures. Additional information for healthcare providers can be found at https://www.cdc.gov/legionella/clinicians.html [CDC 2017a]

Employers and Building Managers

For information about developing a water management program to reduce Legionella growth, consult CDC 2018c. In 

this setting, such a program could include the following*:

 Identifying and addressing areas of water stagnation, lowflow, and low levels of or no disinfectant

 Regularly measuring residual disinfectant levels in municipal water supplied to the facility and at distal points 

of use throughout the facility in both hot and cold water 

systems.

 Improving surface drainage to eliminate standing water

 Keeping grounds clear of debris to facilitate drainage

 Monitoring and maintaining disinfectant levels and appropriate temperatures

* Healthcare facilities have additional considerations when developing a 

water management program to reduce Legionella growth.

Refer to the CDC toolkit and the OSHA Legionellosis webpage to identify potential sources of Legionella [CDC 2018c; 

OSHA 2018].

Develop and implement maintenance plans for all equipment.

Follow manufacturer guidelines on the safe use of disinfectants.

Develop and implement worker protection requirements 

following the hierarchy of controls that first relies on engineering controls and administrative controls, and then considers personal protective equipment (i.e. respirators). 

Use respiratory protection if necessary to reduce exposure to 

aerosols that could contain Legionella. According to the hierarchy of controls, respirators should be used only when the 

hazards are not controlled by engineering and administrative controls [NIOSH 2016b]. Set up a respiratory protection 

program that includes all required elements in the OSHA 29 

CFR 1910.134 respiratory protection standard [OSHA 2011].

Use an experienced company to perform environmental 

sampling. More information about working with consultants 

can be found in CDC 2018a. 

Contact your state or local health department for additional support and resources to manage Legionella in the workplace. 

Encourage employees to report any respiratory problems to 

supervisors or managers, and healthcare providers. 

Have employees who work around processes that use water 

or create mist evaluated by a healthcare provider for possible 

Legionnaires’ disease if they develop signs or symptoms that 

might be pneumonia. 

Acknowledgments

This document was prepared by Nancy Burton, PhD, Division of Field Studies and Engineering and Susan Afanuh, Division of Science Integration, National Institute for Occupational Safety and Health.

Suggested Citation

NIOSH [2019]. Preventing occupational exposure to Legionella. By Burton N, Afanuh S. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety 

and Health, DHHS (NIOSH) Publication No. 2019-131, DOI: 

https://doi.org/10.26616/NIOSHPUB2019131.
4 

References

AIHA [2015]. Recognition, evaluation, and control of Legionella in building water systems. Falls Church, VA: American Industrial Hygiene Association.

ASHRAE [2018]. ANSI/ASHRAE Standard 188-2018: Legionellosis: risk management for building water systems. Atlanta, GA: ASHRAE.

CDC [2016a]. Vital signs: deficiencies in environmental control identified in outbreaks of Legionnaires’ disease—North 

America, 2000–2014. By Garrison LE, Kunz JM, Cooley LA, 

Moore, MR, Lucas C, Schrag, S, Sarisky, J, Whitney, CG. 

MMWR 65(22):576–584.

CDC [2016b]. Legionnaires’ disease. Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. https://www.cdc.gov/legionella/downloads/fs-legionnaires.pdf

CDC [2016c]. Legionnaires’ disease: use water management 

programs in buildings to help prevent outbreaks. Atlanta, 

GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. https://www.cdc.

gov/vitalsigns/pdf/2016-06-vitalsigns.pdf

CDC [2017a]. What clinicians need to know about Legionnaires’ disease. Atlanta, GA: U.S. Department of Health and 

Human Services, Centers for Disease Control and Prevention. https://www.cdc.gov/legionella/downloads/fs-legionella-clinicians.pdf 

CDC [2017b]. Developing a water management program to 

reduce Legionella growth and spread in buildings: a practical guide to implementing industry standards. Atlanta, GA: 

U.S. Department of Health and Human Services, Centers 

for Disease Control and Prevention. https://www.cdc.gov/

legionella/downloads/toolkit.pdf.

CDC [2018a]. Considerations when working with Legionella consultants. Atlanta, GA: U.S. Department of Health 

and Human Services, Centers for Disease Control and Prevention. https://www.cdc.gov/legionella/wmp/consultantconsiderations.html

CDC [2018b]. Signs and symptoms: Legionnaires’ disease. 

Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. https://

www.cdc.gov/legionella/about/signs-symptoms.html

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Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. https://

www.cdc.gov/legionella/maintenance/wmp-toolkit.html

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A, Guerreiro M, Sampaio DA, Vieira L, Machado J, Simões 

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https://doi.org/10.3201/eid1609.100248.

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Water, EPA 810–R–16–001. https://www.epa.gov/groundwater-and-drinking-water/technologies-legionella-control-premise-plumbing-systems

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of Legionnaires’ disease risk and other health hazards at an 

offset printing company. By Casey M, Hawley Brie. Cincinnati, OH: U.S. Department of Health and Human Services, 

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0065-3252.pdf

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niosh/topics/hierarchy/

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Valero N, de Simón M, Gallés P, Izquierdo N, Arimon J, 

González R, Manzanares-Laya S, Avellanes I, Gómez A 

[2017]. Street cleaning trucks as potential sources of Legionella pneumophila. Emerg Infect Dis 23(11):1880–1882, doi: 

10.3201/eid2311.161390.
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DOI: https://doi.org/10.26616/NIOSHPub2019131

DHHS (NIOSH) Publication No. 2019-131

September 2019