Legionella Under the Microscope: How Industry Standards and Expert Services Help Safeguard Healthcare Facilities

By: John LeJeune

A Growing Threat in Healthcare Facilities

Legionnaires' disease is a severe form of pneumonia associated with inhalation or aspiration of aerosolized water droplets contaminated with Legionella bacteria, most commonly Legionella pneumophila. Reported U.S. cases have generally increased since the early 2000s, with a national peak in 2018, a decline during the first year of the COVID-19 pandemic, and a rebound in 2021. Centers for Disease Control and Prevention (CDC) surveillance data continue to show sustained concern, with 2024 and 2025 data identified as provisional in current CDC public reporting (Fig. 1).

Cases per 100,000 population

Figure 1. Reported U.S. Legionnaires' Disease Incidence, 2000-2025

Source: CDC, Legionellosis Surveillance and Trends, "Legionnaires' Disease in the United States: 2000-2025," updated July 8, 2026. Data are based on the National Notifiable Diseases Surveillance System; recent years, including 2024 and 2025, are identified by CDC as provisional and subject to change.

The decrease in reported cases during the first year of the COVID-19 pandemic should be interpreted cautiously. Reported counts may have been influenced by changes in healthcare-seeking behavior, reduced diagnostic evaluation for non-COVID-19 respiratory illness, delayed or disrupted public health reporting, and lower building occupancy that altered water use patterns. Therefore, the observed decrease should not be interpreted as confirmation that Legionella exposure risk declined during that period.

Healthcare-associated Legionnaires' disease warrants particular attention because patients and residents may be older, immunocompromised, or otherwise medically vulnerable. CDC reports that healthcare-associated cases can be especially severe, with an estimated case-fatality rate of approximately 25% for definite healthcare-associated cases compared with approximately 10% for cases that are not healthcare-associated. Risk can be amplified by complex plumbing systems, aging infrastructure, water stagnation, low disinfectant residuals, biofilm, sediment, scale, and building modifications that create dead legs or low-flow conditions. Given the continued public health concern, elevated risk in healthcare settings, and aging hospital and long-term care infrastructure throughout the country, robust water management practices are essential for these facilities that serve vulnerable populations.

Current prevention guidance emphasizes that a water management program should function as an active risk-management system, not simply as a written plan. Effective programs define control limits, monitor key parameters, document corrective actions, verify that required activities are completed, validate that the program is reducing risk, and maintain records that can support internal review, accreditation review, regulatory inquiry, or outbreak response.

Combating Legionella

Reducing potential exposure to Legionella begins with establishing a competent water management team. At a minimum, the team should include representatives with authority and practical knowledge, including:

• An owner or administrator with authority to make administrative and financial decisions
• Management staff responsible for implementing and updating the program
• Communications personnel responsible for timely and appropriate internal and external communication
• Qualified consultants who can identify hazards, evaluate testing parameters, and provide technical recommendations
• Maintenance staff who understand the building water systems, history, and operational constraints
• Contractors who can perform repairs, system alterations, or remediation when necessary

The water management team may differ depending on whether the facility is operating proactively or responding to a confirmed case. For example, legal counsel, infection prevention leadership, public health officials, or state and local regulators may need to be involved when a confirmed case of Legionnaires' disease is associated with a facility.

Once the water management team has been established and roles have been defined, the facility should move promptly into evaluation, communication, monitoring, and corrective action. A site-specific water management program should be developed and maintained in alignment with ANSI/ASHRAE Standard 188, CDC guidance, Centers for Medicare & Medicaid Services (CMS) expectations for applicable healthcare facilities, and applicable state or local requirements. At a minimum, the program should include:

• Building and occupancy descriptions, including populations at increased risk
• Water system descriptions, process flow diagrams, and identification of high-risk devices and areas
• Hazard analysis and risk assessment findings, including historical water quality data and sampling results where available
• Defined control measures and control limits, such as temperature, disinfectant residual, pH, flushing frequency, and equipment maintenance requirements
• Monitoring procedures, sampling protocols, corrective action triggers, and response procedures when control limits are not maintained
• Verification, validation, documentation, communication, training, and scheduled program review requirements

The site-specific water management program should be maintained as a "living document." To remain effective, it should be reviewed and updated routinely and whenever building conditions, water system operations, occupant risk, or regulatory expectations change.

Services That Make a Difference

GBTS supports healthcare and long-term care facilities by helping translate technical guidance and regulatory expectations into practical, facility-specific water management practices:

• Facility-specific water system risk assessments
• Development, implementation, and periodic review of water management programs
• Training for leadership, facilities, maintenance, infection prevention, and on-site staff
• Water quality monitoring, Legionella sampling coordination, and interpretation of results in context with the facility's program
• Corrective action planning, interim controls, remediation oversight, and post-corrective-action verification
• Regulatory, accreditation, infection prevention, and documentation support

With Legionnaires' disease remaining a public health concern and regulatory scrutiny continuing, healthcare and long-term care facilities should prioritize water safety before a case or outbreak occurs. Is your facility prepared? Now is the time to review water systems, confirm that control measures are measurable and documented, train staff, and implement or update a comprehensive water management program.

Regulatory and Technical References

• 42 CFR § 482.42 — Hospitals: Requires hospitals to provide a sanitary environment and maintain an active program for the prevention, control, and investigation of infections and communicable diseases
• 42 CFR § 80 — Skilled nursing facilities and nursing facilities: Requires facilities to establish and maintain an infection prevention and control program designed to provide a safe, sanitary, and comfortable environment and help prevent the development and transmission of communicable diseases and infections
• 42 CFR § 635(a)(3)(vi) — Critical access hospitals: Requires policies that include a system for identifying, reporting, investigating, and controlling infections and communicable diseases of patients and personnel
• CMS Survey and Certification Memorandum, June 2, 2017, revised July 6, 2018: "Requirement to Reduce Legionella Risk in Healthcare Facility Water Systems to Prevent Cases and Outbreaks of Legionnaires' Disease."

Industry Guidelines/Documents

• Recognition, Evaluation and Control of Legionella in Building Water Systems; American Industrial Hygiene Association (AIHA), 2015.
• ANSI/ASHRAE Standard 188, Legionellosis: Risk Management for Building Water Systems; American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), current standard, with ongoing addenda and maintenance.
• ASHRAE Guideline 12, Managing the Risk of Legionellosis Associated with Building Water Systems. ASHRAE, 2023.
• Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings: A Practical Guide to Implementing Industry Standards; CDC; Version 1.2, September 30, 2025.
• ANSI/ASHRAE Standard 514, Risk Management for Building Water Systems: Physical, Chemical, and Microbial Hazards, ASHRAE; current water system risk management framework addressing broader opportunistic waterborne pathogens and related hazards.