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Overview

What Is Legionellosis?

Legionellosis is an infection caused by Legionella bacteria, which can grow in certain water systems and reach people through contaminated droplets or inhaled water. Its two main forms are Legionnaires’ disease, a potentially serious type of pneumonia, and Pontiac fever, a milder flu-like illness that does not cause pneumonia. Older adults, smokers, and people with chronic lung disease, diabetes, cancer, kidney disease, liver disease, or a weakened immune system are more likely to become seriously ill.

Symptoms

Symptoms of Legionellosis

  • Fever
  • Cough
  • Shortness of breath
  • Muscle aches
  • Headache
  • Fatigue
  • Nausea
  • Diarrhea
  • Confusion

Pontiac fever usually causes a milder flu-like illness, often with fever, chills, muscle aches, and headache, but it does not cause pneumonia. It generally improves more quickly than Legionnaires’ disease, while Legionnaires’ disease can cause worsening breathing problems and severe illness.

How It Spreads

How Legionellosis Spreads

Legionella bacteria can multiply in warm, stagnant, or poorly maintained water systems. People may become infected when contaminated water is turned into fine droplets or mist that they breathe in, or when water accidentally enters the lungs during swallowing or drinking.

  • Showers and faucets can release contaminated water droplets that are inhaled.
  • Hot tubs can spread Legionella through aerosolized water when they are not properly maintained.
  • Cooling towers can produce contaminated mist that travels through the air around large buildings.
  • Decorative fountains can create droplets from water that contains Legionella bacteria.
  • Complex or poorly maintained plumbing systems can allow bacteria to grow and spread.
  • Respiratory therapy equipment can cause exposure if it is contaminated or not cleaned as directed.
  • Contaminated soil or potting mix may be a source of exposure in some circumstances.

Risk Factors

Who Has a Higher Risk for Legionellosis

  • Older age increases the risk of serious illness and is not a factor a person can change.
  • Smoking increases risk and is a modifiable factor; quitting can improve overall lung health.
  • Chronic lung disease, including chronic obstructive pulmonary disease, can increase vulnerability.
  • Diabetes can increase the likelihood of severe infection.
  • Kidney or liver disease can make complications more likely.
  • Cancer and some cancer treatments can weaken the body’s defenses.
  • A weakened immune system, including from certain medicines or medical conditions, raises risk.
  • Exposure to complex or poorly maintained water systems can increase the chance of encountering Legionella bacteria.

Risk also rises after exposure to poorly maintained or complex water systems, especially in health care facilities, hotels, long-term care settings, workplaces, and large residential buildings. These settings may have extensive plumbing, cooling equipment, or water storage areas where bacteria can multiply.

Complications

Complications of Legionellosis

  • Severe pneumonia can progress to respiratory failure requiring intensive breathing support.
  • Sepsis can occur when the infection causes a dangerous whole-body response.
  • Acute kidney injury can develop during severe infection or systemic illness.
  • Encephalopathy can cause confusion or changes in brain function.
  • Prolonged weakness and fatigue may continue after the infection improves.
  • Death is possible in severe cases, particularly when treatment is delayed or serious medical conditions are present.

Complications are more likely in older adults and people with underlying illness or a weakened immune system. Early medical evaluation and prompt treatment are important when Legionnaires’ disease or another severe form of Legionellosis is suspected.

Diagnosis

How Legionellosis Is Diagnosed

Clinicians consider a person’s symptoms, recent travel or water exposures, and findings from a chest examination or imaging. They use targeted laboratory testing to confirm Legionella infection and assess whether pneumonia or another serious complication is present.

  • A urinary antigen test can detect evidence of some Legionella infections.
  • Culture or molecular testing of respiratory samples can identify Legionella from material coughed up or collected from the airways.
  • Chest imaging can show pneumonia or other changes in the lungs.
  • Blood tests can help evaluate inflammation, infection, and organ function.
  • Oxygen assessment, including pulse oximetry, helps show how well the lungs are supplying oxygen.

Treatment & Management

Treatment and Management of Legionellosis

Suspected or confirmed Legionnaires’ disease is treated with prescription antibiotics chosen by a clinician. Treatment is usually started promptly when the illness is strongly suspected rather than waiting for every test result, because early treatment can be important in serious infection.

  • Fluids may be given to help maintain hydration and support circulation.
  • Fever control can improve comfort while the infection is treated.
  • Supplemental oxygen may be needed when blood oxygen levels are low.
  • Clinicians may monitor breathing, kidney function, and other organ functions.
  • Hospitalization may be needed for pneumonia, low oxygen levels, or significant underlying illness.
  • Intensive care or mechanical ventilation may be required when breathing or organ function becomes severely impaired.

Prevention

Preventing Legionellosis

  • Building owners and managers should maintain water systems according to appropriate water-management plans.
  • Hot tubs should be cleaned, disinfected, and monitored according to public health and manufacturer guidance.
  • Preventing stagnant water can reduce conditions that allow Legionella bacteria to grow.
  • Humidifiers and respiratory equipment should be cleaned and used according to the manufacturer’s instructions.
  • Avoid hot-tub exposure when the system is visibly dirty, poorly maintained, or not being properly disinfected.

There is no routinely recommended vaccine or general population screening test for Legionellosis. Coordinated water-management programs are especially important in health care facilities, long-term care settings, hotels, and other places where many people or high-risk individuals may be exposed.

Outlook and Prognosis

Outlook and Prognosis

Pontiac fever is usually self-limited and resolves without causing pneumonia. Legionnaires’ disease can be severe, but many people improve with appropriate antibiotic treatment; recovery may take weeks or longer, and weakness or fatigue can continue after the infection is controlled.

  • Older age is associated with a higher risk of severe illness and a more difficult recovery.
  • Immune status affects how well the body can control the infection.
  • Underlying disease, such as lung, kidney, liver, or heart disease, can influence the outlook.
  • The severity of pneumonia affects the likelihood of hospitalization and prolonged recovery.
  • Organ involvement can signal a more serious illness and a greater risk of complications.
  • How quickly effective treatment begins can influence recovery and disease severity.

When Should You See a Doctor

When Should You See a Doctor?

Get medical advice promptly

Legionella exposure

Seek prompt medical evaluation for fever, cough, shortness of breath, diarrhea, confusion, or worsening illness after possible exposure to a hot tub, building water system, health care facility, or another suspected source. Tell the clinician about the possible exposure, especially if you are an older adult, smoke, or have a chronic illness or weakened immune system.

  • Severe trouble breathing requires emergency care.
  • Bluish lips or skin may indicate dangerously low oxygen.
  • Chest pain should be assessed urgently.
  • New confusion can be a sign of severe infection or low oxygen.
  • Fainting requires immediate medical attention.
  • Inability to stay awake is an emergency symptom.
  • Signs of severe dehydration, such as very little urine or extreme dizziness, need urgent care.

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