Legionnaires' Disease Symptoms and Treatment
Legionnaires’ disease is a pneumonia, and it presents like one. That is the central difficulty with it. Someone with Legionnaires’ disease looks much like someone with any other serious chest infection — and, as CDC states directly, the illness cannot be distinguished from other pneumonias either by examination or by chest X-ray.
The distinction matters because the treatment differs. The antibiotics most commonly reached for first in pneumonia do not work against Legionella. Without a specific test, a patient can be treated attentively and still not be treated effectively.
If you are being treated for pneumonia and are not improving, it is reasonable to ask your doctor whether you have been tested for Legionnaires’ disease specifically. It is a distinct test, and it is not part of routine pneumonia care everywhere.
Early symptoms
Symptoms usually begin two to fourteen days after exposure. The first signs are often mistaken for flu:
- Headache
- Muscle aches
- Fever, which can climb above 104°F
[VID-02 — symptoms explainer video slot]
Symptoms that follow
Within a day or two, the illness typically declares itself as a chest infection:
- Cough, sometimes bringing up mucus, occasionally blood
- Shortness of breath
- Chest pain
- Nausea, vomiting or diarrhoea
- Confusion or other changes in thinking and alertness
That last one is worth noting. Confusion is not a symptom people associate with a lung infection, and in older patients it is easily attributed to something else. It is one of the features that should prompt a doctor to consider Legionnaires’ disease.
The exposure window
Symptoms usually appear two to fourteen days after exposure. If you become unwell with these symptoms within about two weeks of staying in a hotel, being admitted to hospital, using a spa pool, or spending time in a building where Legionnaires’ disease has been reported, tell your doctor where you have been. That exposure history is often what prompts the right test.
When to seek care
Legionnaires’ disease is treatable, and most people who are treated recover. Getting care early matters more than getting it perfectly.
Seek medical attention if you have a fever with a cough and shortness of breath, particularly if you are over 50, smoke or used to smoke, have a chronic lung condition, or have a weakened immune system. Seek urgent care if you are struggling to breathe, have chest pain, or become confused or unusually drowsy.
How it is diagnosed
CDC recommends two tests run together.
The urinary antigen test looks for a fragment of the bacterium in a urine sample. It is quick, widely available, and the test most commonly used. Its limitation is that it typically detects only Legionella pneumophila serogroup 1 — the most common cause, but not the only one. A negative result does not entirely rule the disease out.
A lower respiratory sample, cultured or tested by molecular methods, catches what the urine test can miss. Culture is slower and requires specialised media, but it does something no other test does: it produces a bacterial isolate from the patient that can be compared against samples taken from a suspect water system.
That comparison is how a source is confirmed. Without it, an investigation may identify a likely building but never prove it — and a system that is never proven to be the source is rarely required to be fixed. This is why the second test matters beyond the individual patient.
[Editorial note: the source site’s FAQ describes DFA staining and paired antibody titres. CDC no longer recommends serological testing in most situations. That material has been dropped rather than migrated.]
Treatment
Legionnaires’ disease is treated with antibiotics — specifically those effective against Legionella, which include the macrolide and fluoroquinolone classes. Most people need hospital care, and treatment usually runs one to two weeks depending on severity and how the patient responds.
Choice of antibiotic, dose and duration are decisions for a treating clinician. What matters from a patient’s perspective is that the right class is prescribed, and that depends on the diagnosis being made.
Complications
Legionnaires’ disease can be severe. Possible complications include respiratory failure, septic shock and acute kidney failure.
About one in ten people who get Legionnaires’ disease die from the infection. For those who catch it during a stay in a healthcare facility, it is closer to one in four — because those patients are, by definition, already unwell.
Pontiac fever
Everything on this page describes what happens after exposure. None of it needed to happen.
Legionella reaches people through building water systems that were not being actively managed. The controls that prevent that are established, published and well understood. Where they are required and followed, this disease largely does not occur.
Know when it happens near you
We send occasional alerts on outbreaks, legislation and new research. No more than that.
Medical disclaimer: This page provides general public health information and is not medical advice. It cannot substitute for diagnosis or treatment by a qualified clinician. If you believe you have been exposed to Legionella or are experiencing symptoms, contact a doctor or your local health department.