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Legionnaires' disease is a serious lung infection (a type of pneumonia) caused by Legionella bacteria. People catch it by breathing in tiny droplets of contaminated water — for example from cooling towers, warm-water systems or spa pools — or, in Australia, from potting mix and compost. It is not spread from person to person. It causes high fever, cough and breathlessness and needs prompt antibiotics; some people become very unwell. This page explains the illness, its treatment, and the physiotherapy role in recovery.
Definition
Legionnaires’ disease is a pneumonia caused by Legionella bacteria — most commonly Legionella pneumophila, usually acquired from engineered water systems, and in Australia distinctively also Legionella longbeachae, associated with potting mix and compost. It is a notifiable disease. A milder, self-limiting influenza-like illness without pneumonia, caused by the same organisms, is called Pontiac fever.
Pathophysiology
An intracellular infection
Inhaled or aspirated Legionella reach the alveoli, where they are engulfed by alveolar macrophages. Rather than being destroyed, the bacteria subvert the normal destruction pathway and replicate freely inside the macrophage — the same trick they use to survive inside freshwater amoebae, which is where they evolved it. This intracellular niche is why beta-lactam antibiotics fail: they do not penetrate cells adequately, and treatment requires agents that concentrate intracellularly.1
Why the pneumonia is severe
Eventual macrophage lysis releases large bacterial loads and provokes an intense neutrophilic inflammatory response, producing dense alveolar consolidation, impaired gas exchange and often rapid progression to respiratory failure. The systemic cytokine response accounts for the striking extra-pulmonary features — confusion, diarrhoea, hyponatraemia and deranged liver enzymes — that distinguish it clinically from more typical pneumonias.
How exposure happens
Legionella multiplies in warm, stagnant water between roughly 20 and 45 °C, particularly within biofilm in cooling towers, warm-water systems, spa pools and complex plumbing. Infection follows inhalation of contaminated aerosol, or of dust from potting mix in the case of L. longbeachae. It is not transmitted person to person, which is worth stating plainly to patients and families.
Co-morbidities
Severe disease is more likely in people with chronic lung disease, diabetes, chronic kidney or liver disease, heart disease, malignancy or immunosuppression — particularly corticosteroids and tumour necrosis factor inhibitors — and in current smokers and adults over 50. These groups are more prone to respiratory failure, to acute kidney injury, and to a slower and less complete recovery.
Prevalence
Legionnaires’ disease accounts for a small percentage of community-acquired pneumonia overall but a disproportionate share of severe cases requiring intensive care. Several hundred cases are notified in Australia each year, with a distinctive local pattern: L. longbeachae from potting mix and compost causes roughly half of Australian cases, a much higher proportion than in Europe or North America. Because the urinary antigen test detects only L. pneumophila serogroup 1, this pattern has direct diagnostic consequences.2
Causes and risk factors
- Aerosol exposure — cooling towers and air-conditioning systems, warm-water and shower systems, spa pools, decorative fountains, humidifiers and respiratory equipment filled with tap water.
- Potting mix and compost — the characteristic Australian route, through inhaled dust; gardeners are a recognised at-risk group.
- Age over 50 and male sex.
- Smoking — a strong and dose-related risk factor.
- Chronic disease and immunosuppression as above.
- Recent travel or hotel, cruise or hospital stay, which is why an exposure history over the preceding ten days is taken in every case.
- Aspiration of contaminated water in hospital patients with swallowing impairment.
Symptoms
Typical features
Onset two to ten days after exposure, with high fever, rigors, severe headache and prominent myalgia, followed by a cough that is often dry at first and becomes productive, with breathlessness and pleuritic chest pain. Patients frequently look considerably more unwell than the chest signs alone would suggest.
Extra-pulmonary clues
The classic triad prompting suspicion is confusion, diarrhoea and hyponatraemia in someone with pneumonia. Nausea, vomiting, abdominal pain and relative bradycardia may accompany them. None is specific, but together in a severe pneumonia they should trigger Legionella testing and appropriate empirical cover.
Rapid deterioration
Progression to severe hypoxaemic respiratory failure and acute respiratory distress syndrome can occur over 24 to 48 hours, and is more likely where the diagnosis is delayed and initial antibiotics do not cover Legionella.
Warning signs
Diagnosis
Why diagnosis matters
Because Legionella is not covered by the penicillins commonly used first-line for pneumonia, specific diagnosis directly determines whether treatment works. It also triggers notification and public-health investigation of the source, which can prevent an outbreak. Guidelines recommend testing for Legionella in severe community-acquired pneumonia, in intensive care admissions, and where there is a suggestive exposure history.3
How is it diagnosed?
The urinary antigen test is rapid, widely available and remains positive for weeks — but detects only L. pneumophila serogroup 1. A negative urinary antigen does not exclude Legionnaires’ disease in Australia, because it will not detect L. longbeachae. This single point causes more missed diagnoses here than any other.
Culture and molecular testing
Sputum PCR detects all species and serogroups and is the test that matters where potting-mix exposure is possible. Culture on selective medium remains valuable because it provides an isolate for genomic comparison with environmental samples, which is what allows public health to confirm a source. Paired serology is retrospective and of limited use acutely.
Radiology
Chest imaging shows consolidation, frequently unilateral at first and often progressing despite appropriate treatment during the first few days — a recognised feature that should not by itself prompt a change of antibiotic. Radiographic resolution characteristically lags clinical recovery by weeks to months.
Investigations for related conditions
Bloods commonly show hyponatraemia (more marked than in other pneumonias), raised creatine kinase, deranged liver enzymes, raised inflammatory markers and acute kidney injury. Oxygenation is assessed formally. A careful exposure history covering the preceding ten days — gardening and potting mix, spas, hotels, cruises, cooling towers near work or home, hospital stay — is part of the diagnostic workup, not an administrative extra.
Management
Management and goals
Goals are to start effective antibiotics quickly, support gas exchange, manage the systemic complications, identify the source through public health, and rehabilitate through a recovery that is frequently prolonged. Speed to appropriate antibiotic is the strongest determinant of outcome.
Antibiotics
Treatment is with an agent that penetrates cells: a fluoroquinolone such as levofloxacin, or a macrolide such as azithromycin. Standard penicillins and cephalosporins are ineffective. Australian antibiotic guidance sets out the current regimens and durations, which are typically longer than for uncomplicated pneumonia — commonly seven to ten days, and extended to three weeks in immunocompromised or severe disease.4
Oxygen and respiratory support
Supplemental oxygen, escalating to high-flow nasal oxygen, non-invasive or invasive ventilation as required. Where severe ARDS develops, lung-protective ventilation and prone positioning apply — prone positioning significantly reduced mortality in severe ARDS in a landmark randomised trial.5
Critical care and early rehabilitation
A significant minority require intensive care. Early physical and occupational therapy during sedation interruption improves return to independent function and reduces delirium and ventilator days,6 and is applied here as in any critical illness — particularly relevant given how prolonged recovery from this pneumonia tends to be.
Public health notification
Notification is mandatory and immediate. Public health traces the source through environmental sampling and genomic matching, which can identify a cooling tower or water system affecting many people. Clinicians contribute the exposure history that makes tracing possible.
Identifying deterioration
Rising oxygen requirement, confusion, falling urine output, worsening hyponatraemia or a rising creatine kinase all indicate progression. Radiographic worsening in the first few days is expected and is judged alongside the clinical trajectory rather than in isolation.
Medications
Medications for Legionnaires’ disease
A fluoroquinolone or macrolide is the specific treatment, with the choice influenced by severity, drug interactions and QT-interval risk. Supportive medication addresses fever, nausea, electrolyte correction and fluid balance. Corticosteroids have no established role except where indicated for another reason.
Correct use of medications
The course is longer than for typical pneumonia and is completed in full, since relapse is described with truncated treatment. Both drug classes prolong the QT interval and interact widely — fluoroquinolones additionally carry tendon and neuropsychiatric risks that warrant discussion in older patients. Renal function is monitored given the frequency of acute kidney injury.
Prevention rather than treatment
Most of the useful pharmacology here is environmental engineering rather than medicine: water-system maintenance, temperature control and cooling-tower management, all regulated in Australia. For individuals, safe potting-mix handling is the practical preventive measure and is covered below.
Multi-system manifestations
Neurological
Confusion and delirium are common enough to be diagnostic clues. Headache is often severe. Less commonly, cerebellar signs including ataxia and dysarthria occur and may persist for months after recovery — a genuine and under-recognised rehabilitation problem.
Gastrointestinal and hepatic
Diarrhoea, nausea, vomiting and abdominal pain occur in a large proportion of cases, sometimes preceding respiratory symptoms and leading to an initial gastrointestinal diagnosis. Transaminases are frequently elevated.
Renal and electrolyte
Hyponatraemia is characteristic and more pronounced than in other pneumonias. Acute kidney injury occurs from a combination of sepsis, dehydration and, occasionally, rhabdomyolysis.
Muscle
Prominent myalgia, raised creatine kinase and, in severe cases, rhabdomyolysis. Muscle weakness contributes substantially to the functional deficit during recovery.
Cardiac
Relative bradycardia despite high fever is a classic sign. Myocarditis, pericarditis and endocarditis are described but uncommon, and arrhythmia risk is compounded by the QT-prolonging antibiotics used to treat the infection.
Persistent fatigue and psychological sequelae
Long-term consequences are well documented. Survivors of a Legionnaires’ disease outbreak had significantly impaired health-related quality of life and a high prevalence of post-traumatic stress and depressive symptoms well after the acute illness, with fatigue and neurological symptoms persisting for many months.7 This is not simply deconditioning, and it should be anticipated rather than discovered.
Living with Legionnaires’ disease
A prolonged recovery
Recovery from severe pneumonia takes weeks to months, with fatigue, breathlessness on exertion and reduced concentration persisting well beyond hospital discharge. Setting that expectation early prevents the discouragement that follows an assumption of two weeks.
Fatigue, mood and cognition
Persistent fatigue, low mood, anxiety and post-traumatic symptoms are common after severe illness and after an outbreak, where fear and media attention compound it.7 Screening for them, and normalising them, is part of follow-up rather than an optional extra.
Nutrition and sleep
Weight and muscle loss during a severe febrile illness are substantial. Protein-adequate intake and dietetic input where loss has been marked support rehabilitation, and disrupted sleep is treated as part of recovery rather than a separate complaint.
Safe gardening and re-exposure
For the Australian L. longbeachae route this is the key advice: dampen potting mix before use, open bags away from the face and with the opening directed away, wear a P2 mask and gloves, work in a well-ventilated area, avoid dry sweeping of spilled mix, and wash hands thoroughly afterwards. Bags carry a warning label for this reason.
Return to work and activity
Graded, guided by fatigue rather than a date. Those in physically demanding work often need a longer and more staged return than they expect, and written advice to the employer helps.
Prognosis
With prompt appropriate antibiotics most people recover, but Legionnaires’ disease is a serious pneumonia: mortality is around 5–10% in community cases and considerably higher in those requiring intensive care, in nosocomial infection and in immunocompromised patients. Delay to effective antibiotic is the strongest modifiable determinant. Among survivors, radiographic and functional recovery is slow, and a substantial proportion report fatigue, reduced exercise tolerance and neurocognitive symptoms months later — which makes structured rehabilitation, rather than discharge with reassurance, the appropriate endpoint of care.
Role of the physiotherapist
In the acute phase the contribution is positioning, oxygen therapy support, and early mobilisation as soon as physiological stability allows. Where secretions are retained, airway clearance is indicated, though the evidence for routine chest physiotherapy in adult pneumonia is limited and effort is better directed at lung expansion, positioning and getting the patient upright. In critical illness the role extends to prone positioning, weaning support and limiting ICU-acquired weakness.
Early mobilisation in hospital is well supported in pneumonia specifically — getting patients out of bed within the first 24 hours of admission significantly reduced length of stay without increasing adverse events.8 After the acute illness, inpatient rehabilitation improves functional capacity, peripheral muscle strength and quality of life in people recovering from community-acquired pneumonia,9 which is directly relevant given how deconditioned these patients become. By contrast, conventional chest physiotherapy techniques do not improve mortality or cure rate in adult pneumonia,10 and are used selectively rather than routinely.
The distinctive feature of this condition is the length and breadth of the recovery. Graded cardiorespiratory rehabilitation over months, fatigue management and pacing, breathing retraining for persistent breathlessness, and attention to the neurological and cognitive sequelae — including balance and coordination work where cerebellar signs persist — are all part of it. Physiotherapists are frequently the clinicians with the most contact time during that phase, and therefore best placed to detect the persistent fatigue, low mood and post-traumatic symptoms that this illness leaves behind, and to refer accordingly.
Part 1 · References
- Cunha BA, Burillo A, Bouza E. Legionnaires' disease. Lancet 2016;387(10016):376–385.
- Whiley H, Bentham R. Legionella longbeachae and legionellosis. Emerg Infect Dis 2011;17(4):579–583.
- Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia: an official ATS/IDSA clinical practice guideline. Am J Respir Crit Care Med 2019;200(7):e45–e67.
- Expert Group for Antibiotic. Therapeutic guidelines: antibiotic. Melbourne: Therapeutic Guidelines Limited; updated June 2026.
- Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome (PROSEVA). N Engl J Med 2013;368(23):2159–2168.
- Schweickert WD, Pohlman MC, Pohlman AS, et al. Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomised controlled trial. Lancet 2009;373(9678):1874–1882.
- Lettinga KD, Verbon A, Nieuwkerk PT, et al. Health-related quality of life and posttraumatic stress disorder among survivors of an outbreak of Legionnaires disease. Clin Infect Dis 2002;35(1):11–17.
- Mundy LM, Leet TL, Darst K, Schnitzler MA, Dunagan WC. Early mobilization of patients hospitalized with community-acquired pneumonia. Chest 2003;124(3):883–889.
- José A, Dal Corso S. Inpatient rehabilitation improves functional capacity, peripheral muscle strength and quality of life in patients with community-acquired pneumonia: a randomised trial. J Physiother 2016;62(2):96–102.
- Yang M, Yan Y, Yin X, et al. Chest physiotherapy for pneumonia in adults. Cochrane Database Syst Rev 2013;(2):CD006338.
References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.
Supervised exercise, breathing technique and self-management education are the mainstay of cardiorespiratory physiotherapy for this condition.
Clinical evidence
Part 1 covers the same condition without the technical detail. What follows is the evidence base behind it, written for clinicians — the literature, the reasoning and the gaps.
For clinicians: this summary supports clinical reasoning and is not a protocol. Check current guidelines and local policy before applying it, and read it alongside the key references and guidelines directory.
Framing. Legionnaires' disease is a severe community-acquired pneumonia with a disproportionate ICU admission rate, treated with a macrolide or fluoroquinolone and diagnosed with urinary antigen plus PCR or culture — noting that urinary antigen detects Legionella pneumophila serogroup 1 and will miss L. longbeachae, which is a major Australian cause associated with potting mix and compost.1,2,3 For physiotherapy the evidence is the same as for pneumonia generally: airway clearance does not alter outcome, mobilisation does.4,5
Diagnosis and treatment
- Antibiotic choice matters and the diagnosis changes it: beta-lactam monotherapy is ineffective, so a macrolide or fluoroquinolone must be included; delay in appropriate therapy is associated with worse outcomes.1,2
- Severity is high: a substantial proportion require ICU admission and mechanical ventilation, with mortality concentrated in older, immunosuppressed and late-treated patients.3
- Extrapulmonary features are characteristic — hyponatraemia, diarrhoea, confusion, deranged liver enzymes and rhabdomyolysis — and are relevant to session safety long before they are relevant to diagnosis.3
- It is a notifiable disease in Australia, with source investigation of cooling towers, warm-water systems and potting mix; the physiotherapist may be the one who elicits the exposure.6
Rehabilitation evidence
- Chest physiotherapy does not improve mortality or cure rate in adult pneumonia — conventional techniques, positive expiratory pressure and osteopathic manipulation all failed to show benefit in the Cochrane review.4
- Early mobilisation shortens hospital stay in community-acquired pneumonia without increasing adverse events — the strongest positive physiotherapy signal in this population.5
- Inpatient rehabilitation improves functional capacity, muscle strength and quality of life after community-acquired pneumonia in randomised comparison with usual care.7
- A prolonged fatigue and neuromuscular symptom tail is well documented after Legionnaires' disease, persisting for months in a substantial minority — graded rehabilitation, not investigation, is the answer for most.8
- Where ARDS supervenes, lung-protective ventilation and prone positioning apply, and early ICU rehabilitation reduces the functional cost of the admission.9,10
Physiotherapy implications
- Do not treat consolidation with clearance techniques. There is no mobile secretion load in the consolidated lobe; percussion and vibration achieve nothing and cost the patient energy.4
- Mobilise from day one within haemodynamic limits — sitting out, standing and short walks, progressed daily. This is the intervention with evidence behind it.5
- Use positioning for oxygenation: upright and side-lying with the good lung dependent in unilateral disease, with oximetry to confirm the response in that individual.
- Treat coexisting airway disease properly — a patient with bronchiectasis or COPD and genuine sputum retention has a real clearance indication, and Legionnaires' does not remove it.
- Be alert to confusion and hyponatraemia: falls risk, poor instruction retention and impaired safety awareness are common, and the session must be adapted rather than abandoned.
- Escalate rising oxygen requirement, respiratory rate above 30, exhaustion, new confusion, or muscle pain with dark urine (rhabdomyolysis).
- Plan the recovery arc explicitly: refer to outpatient rehabilitation, set expectations of weeks to months for fatigue, and use objective measures to demonstrate progress.7,8
Clinical reasoning
- A crackly chest in pneumonia is consolidation, not retained sputum — the distinction determines whether treatment is indicated at all.
- Failure to improve on treatment raises inadequate antibiotic cover, empyema or abscess, and warrants imaging rather than more physiotherapy.
- Ask about gardening and potting mix, recent travel, spas and building water systems — the answer may change public health action as well as the diagnosis.6
- Persistent fatigue at six weeks with normal imaging is expected in this illness; treat it as deconditioning plus post-infective fatigue and rehabilitate accordingly.8
Evidence gaps
- No physiotherapy trial has been conducted specifically in Legionnaires' disease; all evidence is extrapolated from pneumonia and critical-illness populations.4,5
- Optimal timing, intensity and duration of rehabilitation after severe legionellosis are undefined.
- Mechanisms of the prolonged fatigue syndrome, and whether any intervention shortens it, are unknown.8
- Australian L. longbeachae disease is less well characterised than L. pneumophila, including its recovery profile.6
References for the clinical evidence summary
- Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia: an official ATS/IDSA clinical practice guideline. Am J Respir Crit Care Med 2019;200(7):e45–e67.
- Expert Group for Antibiotic. Therapeutic guidelines: antibiotic. Melbourne: Therapeutic Guidelines Limited; updated June 2026.
- Cunha BA, Burillo A, Bouza E. Legionnaires' disease. Lancet 2016;387(10016):376–385.
- Yang M, Yan Y, Yin X, et al. Chest physiotherapy for pneumonia in adults. Cochrane Database Syst Rev 2013;(2):CD006338.
- Mundy LM, Leet TL, Darst K, Schnitzler MA, Dunagan WC. Early mobilization of patients hospitalized with community-acquired pneumonia. Chest 2003;124(3):883–889.
- Whiley H, Bentham R. Legionella longbeachae and legionellosis. Emerg Infect Dis 2011;17(4):579–583.
- José A, Dal Corso S. Inpatient rehabilitation improves functional capacity, peripheral muscle strength and quality of life in patients with community-acquired pneumonia: a randomised trial. J Physiother 2016;62(2):96–102.
- Lettinga KD, Verbon A, Nieuwkerk PT, et al. Health-related quality of life and posttraumatic stress disorder among survivors of an outbreak of Legionnaires disease. Clin Infect Dis 2002;35(1):11–17.
- Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome (PROSEVA). N Engl J Med 2013;368(23):2159–2168.
- Schweickert WD, Pohlman MC, Pohlman AS, et al. Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomised controlled trial. Lancet 2009;373(9678):1874–1882.
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