Legionella grows in lukewarm water in heaters and pipes and reaches the lungs through shower mist. It caused 98% of deaths in US drinking-water outbreaks in 2015–2020 (CDC). Drinking-water filters do not protect against it. What does: a heater kept hot enough, flushing taps that have stood unused, and, for people at high risk, point-of-use membrane filters that are proven in hospitals.
| Source | What it found (quoted) and its limits | Evidence |
|---|---|---|
| CDC. Surveillance of Waterborne Disease Outbreaks Associated with Drinking Water — United States, 2015–2020. MMWR Surveill Summ 73(SS-1) (2024) · new national outbreak surveillance · n = 214 outbreaks |
"214 outbreaks associated with drinking water" caused "at least 2,140 cases of illness, 563 hospitalizations (26% of cases), and 88 deaths (4% of cases)"; Legionella accounted for "786 (37%) of all illnesses, 544 (97%) hospitalizations, and 86 (98%) of all deaths"; 184 (86%) outbreaks were Legionella; individual/private systems "17 (8%)" of outbreaks Route: inhalation (aerosol) and ingestion. What reduces it: Premise plumbing control (temperature, flushing) is where deaths concentrate Limits: Outbreak reporting voluntary; sporadic home cases not captured |
Evidence: strong Free to read · source · added 2026-10-30 |
| CDC. Legionella Control Toolkit — Potable Water Systems module (current) · new agency guidance (buildings) · n = n/a |
Growth band 77–113°F (25–45°C) and "Legionella may grow at temperatures as low as 68°F (20°C)"; "Store hot water at temperatures above 140°F (60°C)." "Ensure hot water in circulation does not fall below 120°F (49°C)." "Flush low-flow piping runs and dead legs at least weekly." Thermostatic mixing valves "will prevent scalding while permitting circulating hot water temperatures above 120°F (49°C)." Route: inhalation (aerosol). What reduces it: Storage ≥140°F with point-of-use mixing valves; weekly flushing of unused fixtures Limits: Written for buildings with water management programs, not single-family homes |
Evidence: strong Free to read · source · added 2026-10-30 |
| CDC. About Legionnaires' Disease (current) · new agency overview · n = n/a |
"People can get Legionnaires' disease when they breathe in mist that contains the bacteria." "About 1 out of every 10 people who gets sick with Legionnaires' disease will die due to complications from their illness." In healthcare settings "about 1 out of every 4 will die." Route: inhalation (aerosol). What reduces it: — Limits: No home-specific numbers |
Evidence: strong Free to read · source · added 2026-10-30 |
| CDC. Legionnaires Disease Associated with a Private-Use Hot Tub in a Vacation Rental Property — New York, October 2024–April 2025. MMWR 75:274-279 (2026) · new outbreak investigation · n = 2 confirmed cases |
L. pneumophila in all three hot tub samples at 134 to 13,677 MPN/mL (culture 3,700 CFU/mL at air-water interface); patient isolate differed from tub isolates by 2-3 SNPs; hot tubs run at ~100°F–104°F, "within the most favorable range for Legionella growth"; sink/shower samples negative by Legiolert Route: inhalation (hot tub aerosol). What reduces it: Automatic disinfectant feed, professional servicing, routine testing; residential spas exempt from NY regulation Limits: Private well supply; 2 cases; rental not owner-occupied |
Evidence: moderate Free to read · source · added 2026-10-30 |
| DC Health. Preventing Legionellosis at Home (fact sheet) (2025) · new state/local health agency guidance (homes) · n = n/a |
"Set water heaters to a minimum of 120°F" (consider 130-140°F); flush faucets/showerheads unused for over a week "for at least 2 minutes"; "Properly maintain and regularly clean all water-using devices"; avoid mist-producing activities such as hot tub use or power washing for those at risk Route: inhalation (aerosol). What reduces it: Heater ≥120°F (higher with anti-scald valve), flush after absence, clean showerheads Limits: Local guidance; no outcome data |
Evidence: moderate Free to read · source · added 2026-10-30 |
| Donohue MJ et al. Widespread molecular detection of Legionella pneumophila serogroup 1 in cold water taps across the United States. Environ Sci Technol (2014) · new environmental survey (qPCR) · n = 68 cold-water taps, multiple US locations |
47% (32 of 68) taps had L. pneumophila sg1 DNA in at least one sample; 11 taps positive in multiple samples; sampled kitchen/bathroom sinks, fountains, a refrigerator dispenser Route: inhalation (potential). What reduces it: — Limits: DNA detection, not culturable/viable organisms; cold taps |
Evidence: moderate Access unknown · added 2026-10-30 |
| Dufresne SF et al. Sporadic Legionnaires' disease: the role of domestic electric hot-water tanks. Epidemiol Infect 140:172-181 (2012) · new case-based environmental investigation · n = 36 homes of sporadic community-acquired cases (Quebec) |
"Legionella was recovered in 12/36 (33%) homes"; 12/33 (36%) electric-heated systems positive; mean 31.4 °C at the tank's lower drainage valve; "The residential and clinical isolates were found to be microbiologically related in 5/36 (14%) patients"; "Contaminated electricity-heated domestic hot-water systems contribute to the acquisition of SCAL" Route: inhalation (shower/tap aerosol). What reduces it: Raise tank setpoint; electric tanks have cold bottom zones — periodic full-tank heating/flush; mixing valve for scald Limits: Quebec electric tanks; small n; may be underestimated per authors |
Evidence: moderate Free to read · source · added 2026-10-30 |
| Sheffer PJ, Stout JE, Wagener MM, Muder RR. Efficacy of new point-of-use water filter for preventing exposure to Legionella and waterborne bacteria. Am J Infect Control 33(5 Suppl):S20-S25 (2005) · new hospital field trial of POU membrane filters · n = 594 samples over 12 cycles |
"No Legionella or Mycobacterium were isolated from the faucets with filters between T = 0 and T = 8 days"; control faucets mean L. pneumophila 10^4.5 CFU/mL Route: inhalation/device. What reduces it: Point-of-use 0.2 µm membrane filter at shower/faucet for high-risk persons Limits: Hospital setting; 8-day filter life in this version; pore size not in abstract; industry links not checked |
Evidence: moderate Access unknown · source · added 2026-10-30 |
Evidence grade: strong = trials, large field studies or official datasets; moderate = smaller or lab studies with real water; weak = single small studies, makers' specs or secondary reports. "Free to read" means the source itself is free to read online.