Introduction
You’ve stayed in that hotel. Marble counters, a rainfall showerhead, the kind of water pressure that makes you forget your own apartment. What you didn’t think about what almost nobody thinks about is the plumbing behind the wall. Warm, still, occasionally neglected. It’s exactly the kind of environment where a bacterium called Legionella likes to set up shop.
Legionnaires’ disease isn’t rare in the way most people assume. As of this week, New York City’s health department is actively investigating a new cluster of cases on Manhattan’s Upper East Side a reminder that this isn’t a historical footnote, it’s a live, ongoing public health issue. Roughly 6,000 cases are reported in the United States every year, and the CDC believes the real number of hospitalizations runs closer to 8,000 to 18,000 people annually, since cases are often underdiagnosed or mistaken for other forms of pneumonia.
This isn’t a piece designed to make you afraid of your own faucet. It’s designed to make you informed enough that you never have to be. Let’s get into what Legionnaires’ disease actually is, how you get it (and, just as importantly, how you don’t), and what prevention actually looks like whether you’re a homeowner, a renter, or someone who just wants to walk into a hotel without side-eyeing the shower.
What Is Legionnaires’ Disease, Exactly?
Legionnaires’ disease is a severe, atypical form of pneumonia caused by Legionella bacteria most often the species Legionella pneumophila. It’s part of a broader family of illnesses called legionellosis, which also includes a much milder cousin: Pontiac fever.
The name itself has a strange origin story. Legionella was discovered after an outbreak in 1976 among attendees of an American Legion convention in Philadelphia, many of whom developed a mysterious, severe pneumonia. The bacteria responsible were eventually isolated and named after the event that made them famous.
Here’s the distinction that matters most, because it changes everything about how seriously you should take a given exposure:
| Feature | Legionnaires’ Disease | Pontiac Fever |
|---|---|---|
| Severity | Severe pneumonia; can be fatal | Mild, flu-like illness |
| Lungs involved | Yes | No |
| Typical duration | Weeks; requires antibiotics | 2 to 5 days, resolves on its own |
| Treatment needed | Yes, specific antibiotics | No, self-limiting |
| Who tends to get it | Older adults, smokers, immunocompromised | Generally healthy people, often in clusters |
Both illnesses come from the same bacteria, which is part of why “which body organ does Legionella affect” is such a common question. The answer is almost always the lungs, Legionnaires’ disease is fundamentally a lung infection, though in rare cases the bacteria can travel further, causing infections in the heart or in open wounds.
How Do People Actually Get Legionnaires’ Disease?
This is where most of the anxiety and most of the misinformation tends to live. So let’s be precise about it.
You get Legionnaires’ disease by breathing in water droplets, or mist, that contain Legionella bacteria. That’s the mechanism, full stop. People typically get sick when they breathe in a mist or vapor contaminated with the bacteria, such as steam from a poorly maintained whirlpool spa. It is not spread through drinking water in the conventional sense (though aspiration accidentally inhaling liquid while swallowing is a documented, if less common, route).
The bacteria thrive in warm, stagnant, or poorly circulated water systems. Here’s where they’re most commonly found:
| Source | Risk Level | Notes |
|---|---|---|
| Cooling towers (large AC systems) | High | Linked to most major outbreaks |
| Hot tubs & whirlpool spas | High | Especially if under-chlorinated |
| Hot water tanks & heaters | Moderate | Risk rises if temperature is too low |
| Large building plumbing | Moderate | Complex, sprawling systems = more stagnant zones |
| Decorative fountains | Moderate | Often overlooked in maintenance schedules |
| Showers & sinks (home) | Low | Rare, but possible if water sits unused for long periods |
| Potting soil | Low | A handful of documented cases tied to gardening |
| Home/car air conditioners | Essentially none | These don’t use water for cooling |
That last line is worth dwelling on, because it directly answers one of the most searched questions on this topic: no, your window unit or car AC is not a meaningful risk. Home and car air conditioners don’t use water for cooling, which is precisely why they don’t provide the environment Legionella needs to multiply. The confusion usually stems from large building cooling towers, which do use water and which are the actual culprits behind most headline-making outbreaks.
As for why you generally don’t catch it from a home shower: it’s not that showers are incapable of harboring the bacteria, it’s that disease depends heavily on the concentration of Legionella in the aerosol and the contamination levels at the source, and most residential water systems simply don’t hit the volume, warmth, and stagnation combination that lets the bacteria flourish the way large commercial systems can.
Is Legionnaires’ Disease Contagious? (No And Here’s Why)
One of the more reassuring facts here, and one worth repeating because it clears up a lot of unnecessary worry: Legionnaires’ disease is not contagious you cannot get it from another person. You can share a room, a meal, even a kiss with someone who has it, and you will not catch it from them the way you would a cold or the flu. Transmission happens through inhaling contaminated, aerosolized water, not through person-to-person contact.
This is also why outbreaks tend to cluster around a shared source a hotel, a hospital, a neighborhood cooling tower rather than spreading outward the way a respiratory virus would. If ten people who all visited the same spa get sick in the same week, the spa’s water system is the story, not each other.
Symptoms: What Legionnaires’ Disease Actually Feels Like
The tricky part about Legionnaires’ disease is that early on, it doesn’t announce itself as anything unusual. It mimics a fairly standard case of pneumonia, which is exactly why it gets missed or misdiagnosed so often.
Symptoms typically begin 2 to 10 days after exposure, though the CDC notes it can occasionally take longer, up to 14 days. The onset is often gradual rather than sudden:
- Fever, sometimes spiking to 104°F (40°C) or higher
- Chills
- Muscle aches and fatigue
- A cough, which may bring up mucus or, in some cases, blood
- Shortness of breath
- Headache
- Confusion (particularly in older adults)
- Gastrointestinal symptoms — nausea, vomiting, diarrhea, and abdominal pain
That gastrointestinal piece surprises people. A lung infection causing diarrhea seems like a mismatch, but it’s actually one of the more useful diagnostic clues doctors look for when they suspect Legionella over a more garden-variety pneumonia. If you’re dealing with a chest infection that also comes with confusion or GI symptoms, that combination is reason enough to specifically ask your doctor about Legionella testing rather than assuming it’s just “a bad flu.”
Can you be exposed and not get sick? Almost certainly, yes and often. Most healthy people exposed to Legionella don’t get sick at all. Whether you develop symptoms depends on the dose of bacteria you inhaled, your overall health, and specific risk factors we’ll get into next.
Who’s Most at Risk?
Not everyone who breathes in Legionella gets Legionnaires’ disease. Risk climbs sharply based on a handful of well-documented factors:
| Risk Factor | Why It Matters |
|---|---|
| Age 50 or older | Immune response and lung resilience naturally decline with age |
| Smoking (current or former) | Damages lung tissue, raising risk for all lung infections |
| Weakened immune system | Includes HIV/AIDS, chemotherapy, or transplant-related immunosuppressants |
| Chronic lung disease | Emphysema, COPD, and similar conditions |
| Diabetes or kidney disease | Associated with higher susceptibility and worse outcomes |
| Recent hospital stay | Hospital water systems require constant, active monitoring |
If you fall into more than one of these categories, it’s worth being a little more deliberate not paranoid, just deliberate about things like hot tub hygiene when you travel, and mentioning any relevant travel or hospital stays to your doctor if you develop pneumonia-like symptoms within two weeks of exposure.
Is Legionnaires’ Disease Curable? What Treatment Looks Like
Yes, and early treatment is the single biggest factor in outcome. Legionnaires’ disease requires treatment with specific antibiotics, and most cases can be treated successfully when identified and treated early. Fluoroquinolones like levofloxacin and newer macrolides such as azithromycin are the standard antibiotic classes used, guided by treatment recommendations from the Infectious Diseases Society of America.
The disease does not resolve on its own the way Pontiac fever does. Left untreated, it can progress into serious territory: respiratory failure, shock, acute kidney injury, and multiorgan dysfunction, with roughly one-third of patients requiring intensive care.
The mortality figures are sobering enough to take seriously without becoming alarmist about them. Legionnaires’ disease carries roughly a 10% death rate overall, though reported mortality actually ranges from 4% to 40% depending on the population studied and how quickly treatment begins which is precisely why doctors emphasize speed of diagnosis so heavily. Catch it early, treat it with the right antibiotic, and the prognosis is generally good. Delay treatment in a high-risk patient, and the calculus changes considerably.
Diagnosis typically starts with a chest X-ray to confirm pneumonia, followed by a urine antigen test and a sputum culture or PCR test to confirm Legionella specifically as the cause. If you’ve recently used a hot tub, traveled and stayed in a hotel, or been in a hospital within the last two weeks and you’re now dealing with pneumonia symptoms, tell your doctor that history explicitly it’s the detail that gets Legionella onto the list of suspects instead of off it.
Prevention: What Actually Reduces Your Risk
Here’s the honest answer to “how do I prevent this”: you, individually, have limited control over most of it, because the real prevention work happens at the building and water-system level. The key to preventing Legionnaires’ disease is reducing the risk of Legionella growth and spread, primarily through water management programs run by building owners and managers. Still, there’s a meaningful list of things within your control, especially at home and while traveling.
At home:
- Water heater temperature is a genuine balancing act, and the CDC is specific about it: keeping your water heater between 130°F and 140°F can kill germs like Legionella, but water that hot can scald skin within seconds. Legionella can actually grow in water anywhere from about 68°F up to 120°F, which is why the commonly used 120°F “scald-safe” setting alone isn’t fully protective the real prevention comes from storing water above 130°F and pairing that with a thermostatic mixing valve at the tap, which blends hot and cold water so you get Legionella-killing storage temperatures without a burn risk at the faucet. This is especially worth getting right if young children or older adults live in your home. Ask your doctor whether raising your setting to 130°F+ with a mixing valve makes sense for your household.
- Run water through faucets, showerheads, and hoses that haven’t been used in a while (after vacation, for instance) before using them normally stagnant water is exactly what lets Legionella take hold.
- Clean and descale showerheads periodically; mineral buildup and biofilm can shelter bacteria.
- Maintain any home hot tub according to manufacturer guidelines, with proper and consistent chlorination.
While traveling:
- If a hotel or rental hot tub looks under-maintained cloudy water, no visible chemical treatment, no maintenance schedule posted, skip it.
- Report any concerns about a property’s water systems to hotel management or, if it feels serious, to the local health department.
For building owners and facility managers:
- Implement a formal water management program, as outlined by CDC’s toolkit for cooling towers, hot water systems, and decorative fountains.
- Register and monitor cooling towers where required by local law (New York City, for example, mandates cooling tower registration).
- Test and maintain proper disinfectant levels consistently, not just after a complaint or an outbreak.
There’s no vaccine for Legionnaires’ disease, and there isn’t likely to be one anytime soon which puts the weight of prevention squarely on maintenance and awareness rather than immunization. That’s a less convenient answer than “get a shot and forget about it,” but it’s the accurate one.
A Word on Recent Outbreaks
If you’ve searched “is there a Legionnaires’ disease outbreak in 2026,” here’s the current, verified picture as of this week. The NYC Health Department is actively investigating a cluster on Manhattan’s Upper East Side (ZIP codes 10028, 10128, and 10075), with 23 confirmed cases and 17 hospitalizations reported so far, and officials pointing to a rooftop cooling tower as the likely source. No deaths have been reported in this cluster to date, and the city has stated the cases aren’t linked to any building’s plumbing residents in the area can continue showering, drinking tap water, and running home air conditioning as normal.
This follows a much larger outbreak last summer centered in Central Harlem, which the city officially closed out at 118 confirmed cases, 92 hospitalizations, and 7 deaths, traced to a dozen contaminated cooling towers across ten buildings, including Harlem Hospital. That outbreak pushed NYC to overhaul its cooling tower law: as of May 2026, building owners must test for Legionella every 31 days while a tower is operating, down from the previous 90-day standard.
Across the border, London, Ontario has dealt with two separate outbreaks in as many years 30 cases and 2 deaths in 2024, followed by 101 cases and 5 deaths in 2025 both traced to the same cooling tower at a Sofina Foods meat-processing plant. That’s now the subject of a proposed $86 million class-action lawsuit filed by Siskinds LLP on behalf of those sickened.
The pattern across all three: warm-weather season, a cooling tower somewhere in the mix, and a delay between exposure and the source being identified. If you want to check current activity in your own city, your local health department’s website is the most reliable source, ahead of social media chatter.
Quick-Reference FAQ
Can you get Legionnaires’ disease from tap water? Directly drinking it, rarely the main risk is inhaling contaminated mist, not swallowing contaminated water, though aspiration during drinking is a documented (uncommon) exception.
Does boiling water get rid of Legionella? Yes. Legionella bacteria are killed at high sustained temperatures; boiling effectively eliminates them, which is part of why water heater temperature matters so much for prevention.
Can bottled water have Legionella? There’s no significant documented history of bottled water as a source of Legionnaires’ disease outbreaks. The bacteria need warm, stagnant conditions to multiply, which sealed, commercially processed bottled water doesn’t provide it isn’t a meaningful risk category compared to cooling towers, hot tubs, and large building plumbing.
Can a CPAP machine cause Legionnaires’ disease? Yes, this is a documented risk, not just a theoretical one. The CDC has found that roughly a quarter of CPAP and humidifier users report filling their devices with tap water, which can carry Legionella along with other waterborne organisms. Case reports exist of Legionella pneumonia traced to CPAP equipment cleaned or filled with tap water instead of distilled. This is exactly why manufacturers specify distilled water for the humidifier chamber and recommend regular cleaning of the mask, tubing, and reservoir.
What’s the difference between Legionnaires’ disease and COVID-19? Both can cause fever, cough, and pneumonia, but Legionnaires’ disease comes from bacteria in water systems (not person-to-person spread), requires antibiotics rather than antivirals, and often comes with distinct GI symptoms like diarrhea alongside the respiratory illness.
Can Legionnaires’ disease become airborne in the traditional sense, like a virus? No, it spreads via aerosolized water droplets from a contaminated source, not through airborne person-to-person transmission the way influenza or COVID-19 can.
What kills Legionella bacteria in water systems? Heat (sustained high temperatures), proper chlorination, and copper-silver ionization systems are the standard tools used in professional water management programs.
The Takeaway
Legionnaires’ disease sits in an unusual spot: serious enough to warrant real respect, common enough to matter, but preventable enough that panic isn’t the right response. Know the sources cooling towers, hot tubs, poorly maintained large plumbing systems. Know the symptoms pneumonia plus confusion or GI upset, especially following travel or hospital stays. And know that if you or someone you love falls into a higher-risk category, the smartest move isn’t avoidance of every shower and hot tub you encounter it’s simply paying attention, asking questions of hotels and facilities when something looks off, and getting to a doctor quickly if something feels wrong.
The bacteria have been around, quietly, since long before 1976. They’re not going anywhere. But neither is the maintenance, the science, and the awareness that keeps them in check.
If you’ve recently traveled, used a hot tub, or been hospitalized and are now dealing with pneumonia-like symptoms, don’t wait it out, mention that history to a healthcare provider explicitly and ask about Legionella testing.
Related Reading:
[8 Ways to Protect Your Family from Salmonella (Before It’s Too Late)] Another common but preventable bacterial threat this one hiding in your kitchen rather than your plumbing.Sources & References
