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LEGIONELLA IN THE US — 2015 TO 2026
Legionella in the United States:
a public health crisis that grows every year
Legionnaires' disease has increased more than fivefold since 2000 and continues to rise.
This page tracks confirmed outbreaks, national case counts, and the documented drivers of that growth - using data directly from the CDC, state health departments, and peer-reviewed research. Updated every week.
US Legionella outbreak tracker
2018 national peak
9,933
CDC confirmed ·
3.04/100k
2021 post-COVID rebound
8,442
CDC confirmed ·
2.54/100k
Estimated 2025 cases
10,500+
CDC trend +
outbreak data
Case fatality rate
~10%
Up to 30% in outbreaks
LEGIONELLA IN THE US — 2015 TO 2026
Cases have risen every decade.
The reasons are documented , and preventable.
Confirmed US cases have grown steadily since 2000 with no sign of reversal.
Peer-reviewed research and CDC surveillance data point to four compounding drivers.
Understanding them is the first step to stopping them.
2015–2017
CDC official PDF
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2020
CDC official table
6,310 confirmed · 1.90/100k
1
2018 — national peak
CDC official PDF
1
2021
CDC official table
1
2022
CDC NNDSS provisional
CDC WONDER — NNDSS Annual Data (2016–2022)PMC scoping review — legionellosis on the rise 2006–2022
NNDSS provisional; finalized figure pending CDC report
1
2025
Estimated - major outbreak year
~10,500+ cases (estimated)
HC Info — Harlem 114/7 · Marshalltown 71/2 · Westchester 37/2 · Orlando 14IWC Innovations — 2025 outbreak year review with case summariesUS News — Harlem NYC outbreak Aug 2025
1
What is Legionella -
and why does it keep spreading?
Legionella pneumophila is a bacterium found naturally in freshwater environments. It becomes dangerous when it colonizes man-made water systems - cooling towers, hot water tanks, showerheads, decorative fountains, and building plumbing networks — where warm, stagnant water allows it to multiply to infectious concentrations.
Infection occurs when a person inhales aerosolized water containing Legionella. The result can be Legionnaires' disease, a severe form of pneumonia with a fatality rate of approximately 10% - rising to 30% in healthcare-associated outbreaks. It is not spread person to person.In the US, Legionnaires' disease is a nationally notifiable condition.
Every confirmed case must be reported to public health authorities. Buildings with complex water systems are required under ASHRAE Standard 188 to maintain a written water management program - yet most do not have one.
Aging infrastructure
Older pipes, dead legs, and building systems past their service life create ideal conditions for Legionella to grow and spread.
Climate change
Warmer temperatures and increased rainfall directly correlate with higher case counts. The Legionella season is getting longer.
Missing water management plans
Most outbreaks occur in buildings without a compliant WMP. ASHRAE 188 compliance remains low across the US.
Aging population
Adults over 50 represent the majority of cases. As the US population ages, the at-risk pool grows year over year.
Read more information about what Legionella is, including resources, case studies, articles, and more.
Disclaimer: This information is provided "as is" for educational purposes only. While sourced from reputable agencies, we make no warranties regarding data accuracy or completeness. We expressly disclaim all liability for any loss or damage arising from reliance on this content. Users should consult professionals for specific medical or safety advice.
EMERGENCY WATER SAFETY RESPONSE
A positive Legionella test is not the end. How you respond in the next 48 hours determines the outcome.
When Legionella is confirmed at a US healthcare or residential facility, the clock starts immediately. CMS, Joint Commission, and state health departments expect documented corrective action at the follow-up inspection — not a work order, not a quote request. Installed, certified POU filters with FDA-registered documentation are what inspectors accept as a Safe Water Protocol. MWT ships same day. Your staff installs in under 5 minutes per fixture. No plumber. No shutdown.
WHAT HAPPENS AFTER YOU CONTACT US
Within 1 hour - our emergency contact responds to your email or call
Same business day - bundle confirmed and dispatched from US warehouse
Under 5 min per fixture - installed by your own staff, no tools, no plumber
Certified documentation ready- FDA, EPA FIFRA, and ASTM F838-20 docs ship with every order