Short answer: no, not in the way most people fear. You cannot catch Legionnaires’ disease from a sick colleague, a relative in the next hospital bed, or anyone sitting near you. It spreads by breathing in contaminated water droplets, not by close contact with an infected person [1][2].
That holds for the overwhelming majority of cases, which is why the NHS describes it as an illness you catch from water rather than from people [2]. Public health bodies stop just short of saying “never”, because a single probable instance of one person passing it to another has been reported in the scientific literature. So the accurate phrasing is “not normally contagious” rather than flatly “never” [1].
For anyone worried about a patient or workmate, that distinction is reassuring. For anyone who runs a building, the message is blunter: the bacteria come from your water, so that is where the control sits.
Myth versus reality: untangling the fear
Most of the worry around this disease comes from treating it like a cold or flu. It does not behave that way. Here is where the common assumption parts company with the evidence.
| Common belief | What the evidence supports |
|---|---|
| You catch it from an infected person, like flu | You catch it by inhaling or aspirating water droplets carrying Legionella; person-to-person spread is not the normal route [1][3] |
| Being in the same room as a patient is risky | The patient is not the source. The shared water system, if there is one, is [3] |
| A sick relative could infect the whole household | Household spread from the patient is not how it works; if others fall ill, suspect a shared water source, not the patient |
| Recovered patients can still pass it on | They were never an infectious source to begin with; they breathed in contaminated aerosol [1] |
| It must be contagious because outbreaks hit many people | Outbreaks happen when many people breathe the same contaminated aerosol, not when they infect each other [3] |
The thread running through that table is simple. When several people get ill, it points to a shared source of contaminated mist, not a chain of infection. That is exactly why outbreak investigations hunt for cooling towers, spa pools, showers and other aerosol-generating equipment rather than tracing who stood next to whom.
The questions people actually ask
Can I catch Legionnaires’ disease from another person?
In ordinary circumstances, no. The disease is not passed by coughing, touching, sharing a room, or caring for someone who has it [1][2]. If you are visiting a relative in hospital with Legionnaires’, you are not at risk from them. The bacteria do not transmit from the patient’s lungs to yours through the air the way a respiratory virus does.
How do you actually catch it, then?
By breathing in, or sometimes accidentally swallowing into the lungs, tiny droplets of water that contain Legionella bacteria [3]. The water has to be aerosolised into a fine mist first, which is why showers, spray taps, cooling towers, spa pools and similar equipment are the usual suspects. Drinking contaminated water is not generally how people get ill; the droplets have to reach deep into the lungs. There is more on the mechanics in How Legionella spreads through water systems.
Has person-to-person transmission ever been recorded?
A single probable case of one person passing the infection to another has been reported in the scientific literature, under unusual circumstances. That one report is why authorities describe person-to-person spread as possible only in rare situations rather than impossible [1]. It is the exception that proves how reliably this disease travels by water and not by human contact. It does not change anything for day-to-day life or for how a building is managed.
Can a family member catch it from a patient cared for at home?
You are not at risk from the patient themselves. The honest caution is different: if a person caught Legionnaires’ from their own home water system, that system is still there, and other people in the house are breathing from the same showers and taps. So the concern at home is the shared water source, not the sick relative. If a case is linked to a home, the water system deserves a proper look.
Do I need to isolate someone with Legionnaires’ disease?
There is no infection-control reason to isolate a patient to protect others from catching it, because it does not spread person to person [1][2]. Clinical decisions about a patient’s care are for their medical team, not something to second-guess from an article. The point worth holding onto is that isolation is not needed to stop transmission to family, carers or other patients.
Is Pontiac fever contagious?
No. Pontiac fever is the milder, flu-like illness caused by the same Legionella bacteria, and it spreads the same way, by inhaling contaminated aerosol rather than from person to person [1]. If you are unsure how the two illnesses differ, Legionnaires disease and Pontiac fever: key differences covers it.
If it isn’t contagious, why do outbreaks affect so many people at once?
Because a single contaminated source can spray infectious mist over a wide area and a lot of people. A cooling tower on a roof, for instance, can carry aerosol some distance on the wind. Everyone who breathes that same mist is exposed independently. It looks like an epidemic of contagion, but it is really many people sharing one source [3]. That is also why finding and shutting down the source matters more than tracing contacts.
A case has been linked to my building. What do I do?
Treat it as a signal that something in the water system may have allowed Legionella to grow and aerosolise. Pull together your risk assessment, temperature records and monitoring history, identify the aerosol-producing outlets that could be involved, and get your responsible person and, where relevant, the relevant authorities engaged early [4]. Whether a work-linked case is reportable under rules such as RIDDOR is a question to settle against current HSE guidance rather than assume.
A caveat worth stating plainly
This explains transmission so you can stop worrying about the wrong thing and focus on the right one. It is not medical advice, and it is not a substitute for a competent, site-specific risk assessment. Whether someone has Legionnaires’ disease, and how they are treated, is for a clinician. Whether your particular water system poses a risk, and what controls it needs, is for a written scheme built around your actual building by someone competent to do it. Use this to ask better questions, not to make diagnoses or sign off a system.
If you only do one thing today
Stop asking whether the person is contagious and start asking where the water came from. If a case is linked to somewhere you are responsible for, find the aerosol-producing outlets nearest the affected person, and ask whether you can prove those outlets were under control. If your evidence lives in a half-filled paper logbook or a spreadsheet nobody has opened in months, that is the gap to close first. Reliable, timestamped records of temperatures and checks are what let you answer the question quickly when it matters, and moving those records into a digital logbook makes them far harder to lose.
Sources
[1] CDC, “About Legionnaires’ Disease”. https://www.cdc.gov/legionella/about/index.html [2] NHS, “Legionnaires’ disease”. https://www.nhs.uk/conditions/legionnaires-disease/ [3] CDC, “How Legionella Spreads”. https://www.cdc.gov/legionella/causes/index.html [4] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm