Yes, in principle you can. Surviving Legionnaires’ disease is not known to give you reliable, lasting immunity, so a fresh exposure to a contaminated water source could infect you again. Your protection comes from clean water and avoiding the aerosol, not from antibodies your last bout left behind.
That answer matters in two directions. If you or a relative has recovered, the reassurance you most want, that it cannot happen again, is not one the evidence supports. And if you manage a building, a prior case among your occupants buys you no safety margin: the person who had it is, if anything, still sitting in the at-risk group.
The “I’ve had it, so I’m safe now” assumption, unpicked
We are wired to expect that one infection means lifelong protection, because that is how chickenpox and measles behave. Legionnaires’ disease does not follow that script, and a handful of specific beliefs cause most of the false comfort.
| The assumption | What the evidence actually supports |
|---|---|
| Having it once makes me immune | No reliable, lasting protective immunity has been established after Legionnaires’ disease; reinfection from a new source is considered possible |
| A second bout would be milder | Severity tracks your susceptibility, age, lung health and immune status, not how many times you have been exposed; a repeat can be just as serious |
| My body now recognises the bug | There are many Legionella species and serogroups, and the dose you inhale plus your underlying health drive the outcome far more than any acquired memory |
| Getting ill again means it “came back” | A genuine reinfection from a fresh exposure is not the same thing as a relapse of an incompletely treated first infection |
Why there is no immunity to bank on
Legionnaires’ disease is a lung infection you catch by breathing in fine droplets of water carrying Legionella bacteria [1]. Unlike measles or chickenpox, it does not pass from person to person, and there is no childhood “you’ve had it, you’re done” pattern to lean on [3]. The immune response people mount afterwards is not well characterised for Legionella, and, crucially, no dependable protective immunity has been demonstrated. Put honestly: recovery clears the current infection; it does not issue a lifetime pass against the next exposure.
Treat any confident claim in either direction with caution. The science here is thinner than for vaccine-preventable diseases, and “you’re immune now” overstates what is actually known about Legionella immunity.
A second bout could be worse, not milder
The instinct that a repeat would be gentler has the mechanism backwards. How badly Legionnaires’ disease hits you depends mostly on who you are when you inhale the bacteria, your age, your lungs, your immune system, and on the dose [2]. Those factors do not improve with time. They tend to hold steady or worsen: people get older, lung conditions progress, immunosuppressing treatments come and go.
So someone who pulled through at 58 with mild COPD is not a safer bet at 64 with worse COPD. If anything they have moved further into the group covered in Who is most at risk of Legionnaires’ disease? Susceptible groups explained. And because the illness can be severe or fatal regardless of history, a second infection deserves the same urgency as the first, as Is Legionnaires’ disease fatal? Mortality, severity and outcomes sets out.
Reinfection is not the same as a relapse
Two things often get lumped together. A relapse is the original infection flaring back because it was never fully cleared, which is a treatment-and-recovery question tied to how the first illness was managed; Legionnaires’ disease incubation period and recovery time covers that arc. A reinfection is a brand-new illness from a fresh inhaled exposure, weeks, months or years later, possibly from a completely different building or water source.
To the patient they can feel identical, the same fever, cough and breathlessness, but they mean different things. Lingering damage from the first episode muddies the picture too, because the kind of breathlessness and fatigue described in Long-term effects of Legionnaires’ disease: recovery and after-effects can be mistaken for a new infection. If symptoms return, that is a question for a doctor, not for guesswork.
Why the “I’m immune now” idea sticks
The belief is intuitive, not foolish. Most infections we meet as children, and the ones we vaccinate against, do leave durable immunity, so we generalise from them. Legionnaires’ breaks the pattern on two counts: you do not catch it from other people, and there is no evidence it trains the body to shrug off the next dose [3]. Layer on the natural relief of having survived something serious, and “it cannot get me again” becomes a comforting story the facts do not underwrite.
What this means for the water system
Here is the part that lands on duty holders. You cannot treat “they have already had it” as a control measure. A recovered occupant carries no protective shield into your building, and is quite likely still in a susceptible group, so the defence stays exactly what it always was: stop the bacteria reaching anyone’s lungs in the first place.
That is what the HSE regime exists to do, keep hot water hot, cold water cold, water moving rather than stagnating, and keep records that prove it [4]. The duty to assess and control the risk under the Approved Code of Practice and guidance (L8) does not flex because an occupant has a prior case [5]. Knowing you have vulnerable people on site, past patients among them, sharpens the argument for tight control rather than relaxing it.
A note on what this page can and cannot tell you
This is general background to help you ask sharper questions, not a diagnosis or a prediction about any individual. Whether a particular person is at risk of a second infection, and what their immune response looked like, is a clinical matter for them and their doctor, and nothing here is medical advice. The control points mentioned are general too: the actual temperatures, frequencies and priorities for your building come from a competent, site-specific Legionella risk assessment, not from a web page.
FAQ
Can you catch Legionnaires’ disease more than once?
Yes, it is possible. Recovering from one infection is not known to give reliable immunity, and because you catch the disease from environmental water rather than from other people, a fresh exposure to a contaminated source can in principle cause a second illness [3].
Does having Legionnaires’ disease make you immune?
There is no established, lasting protective immunity after Legionnaires’ disease. The honest position is that recovery clears that infection but is not a dependable defence against a future one, so treat “you’re immune now” as an overstatement of what the evidence actually supports [1].
If I got it again, would it be less serious?
Not necessarily. Severity is driven by your age, lung health, immune status and the dose you inhale, not by previous exposure [2]. Those risk factors tend to persist or worsen over time, so a repeat infection can be as serious as the first, or worse.
Is reinfection the same as my old infection coming back?
No. A relapse is the original infection returning because it was not fully cleared; a reinfection is a new illness from a fresh exposure. They can feel the same but mean different things, which is why returning symptoms should be assessed by a doctor [1].
What to do next
If you are recovering and worried about catching it again, the productive move is not chasing an immunity test, it is reducing exposure: take any flushing or shower-cleaning advice for your home seriously, and tell a clinician about your history if you fall ill. If you run a building, do not let a recovered occupant lull anyone into easing off. Pull the temperature and flushing records for the outlets serving your most vulnerable users and confirm they are current; a single digital logbook makes those gaps obvious before a fresh exposure finds them.
Sources
[1] NHS, “Legionnaires’ disease”. https://www.nhs.uk/conditions/legionnaires-disease/ [2] CDC, “About Legionnaires’ Disease”. https://www.cdc.gov/legionella/about/index.html [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 [5] HSE, “Legionnaires’ disease. The control of legionella bacteria in water systems - Approved Code of Practice and guidance (L8)”. https://www.hse.gov.uk/pubns/books/l8.htm