Legionnaires' disease: causes, symptoms, transmission, diagnosis, treatment and prevention

Legionnaires’ disease, also known as legionnaires pneumonia, gained its fame during an outbreak in 1976 in Philadelphia, where retired soldiers gatherer at a convention (thus the word “legionnaires”). It was later discovered that the bacteria was transmitted from the central pipeline of the air conditioning system. This type of bacteria caused pneumonia, with frequent symptoms of fever and cough. The main treatment for Legionnaires’ disease is antibiotics.


Legionnaires’ disease is caused by a bacteria named “legionella pneumophila”. This bacteria is commonly found in the soil and water. After exposure to water droplets (such as air conditioner), the bacteria can be inhaled into your lungs. The bacteria in the water may also be accidentally inhaled during drinking. Frequently legionnaires’ disease has been associated with hot tubs, healers, cooling towers in air conditioners, or swimming pools.


Legionnaires’ disease can affect both the young and the old. However, people who are over 50 years, smoke, have previous conditions of lung functional impairment, or have a weak immune system are more susceptible. The symptoms generally develop in 2 to 10 days after exposure to this bacteria. The clinical symptoms are the same with pneumonia caused by other bacteria:

  • Fever and chills;
  • Fatigue;
  • Cough with or without mucus;
  • Shortness of breath;
  • Headache;
  • Muscle aches;
  • Gastrointestinal symptoms, such as vomiting or diarrhea.


Legionnaires’ disease is spread by inhalation of aerosols or water droplets that contain the bacteria. It is generally not transmitted from person-to-person. Patients get legionnaires’ disease because they accidentally inhaled from the water droplets associated with cooling towers in air conditioners, contaminated hot tubs, swimming pools, etc.


Doctors frequently make a diagnosis of pneumonia based upon clinical history and chest x-ray or CT scan results. To specifically detect the pathogen that causes the pneumonia, your doctor may need the following test:

  • Blood or sputum culture: Your doctor would collect your blood or sputum sample to the microbiology lab for further identification.
  • Urine legionella antigens: This detects the legionella in the urine. It is 70-80% sensitive and 100% specific.
  • Your doctor may also collect your sputum or blood sample to do polymerase chain reaction to detect bacterium legionella pneumophila.


Legionnaires’ disease can be cured with antibiotics. Specifically, azithromycin or levofloxacin are very effective and the preferred choice. Depending on the severity, antibiotics can be given orally or intravenously. Most of the legionnaires’ disease need hospitalization. In general, at least 5-10 days of treatment is needed.


Since person-to-person transmission is rare for legionnaires’ disease, infected patients do not need to be isolated.

Disinfect the water supply regularly and vigorously, the contamination surveillance should be routinely carried out.

* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.