Legionnaires' Disease Legionellosis

What is Legionnaires' Disease?

Legionellosis is a waterborne bacterial disease with two forms that are commonly known as Legionnnaires' disease and Pontiac fever. Legionnaires' disease causes a serious form of pneumonia and can be fatal, especially in the elderly. Pontiac fever is a similar but milder disease and does not cause pneumonia or death. Both diseases are caused by bacteria in the genus Legionella. These bacteria grow naturally in warm freshwater environments, such as lakes, rivers, and hot springs. However, transmission of legionellosis is more likely to occur from contact with artificial water systems like hot tubs, showers, decorative fountains, and improperly maintained air conditioning systems. Rare cases of legionellosis have occurred from contact with potting soil.

How do you get Legionnaires' Disease?

Transmission of legionellosis usually occurs following exposure to warm, aerosolised water since the bacteria is inhaled through water droplets in water sprays or mists. Exposure can occur around hot tubs, showers, or inadequately maintained air conditioning cooling towers. Acquiring this disease depends on a number of factors, such as the extent of contamination in the water and the virulence of the particular strain of the bacteria. Person-to-person transmission of legionellosis does not occur.

Susceptibility and Resistance

Factors that increase the risk of acquiring legionellosis include: smoking, diabetes, chronic lung disease, increasing age (greater than 50 years old), and compromised immunity. The disease is more common in males but rare in people younger than 20 years old.

Incubation Period

The incubation period for Legionnaires' Disease is 2-10 days.

What are the Symptoms?

Both Legionnaires' disease and Pontiac fever cause loss of appetite, fatigue, aches and pains, headache, fever, abdominal pain, and diarrhoea.

Legionnaires' disease can be severe and generally progresses into pneumonia and causes a nonproductive cough. Complications in severe cases include respiratory failure, shock, and kidney and multi-organ failure. This disease usually requires hospitalisation and 10 to 15 percent of cases end in death. Recovery from Legionnaires' disease requires treatment with antibiotics and takes several weeks or months.

Pontiac fever does not cause pneumonia or death, and patients usually recover without treatment in 2 to 5 days.

Preventative Measures

There is no vaccine or antibiotics to prevent or treat legionellosis.  Travellers who have an increased risk of infection (elderly, smokers, people with cancer or diabetes, etc.) should avoid high-risk areas such as whirlpool spas, hot tubs, and other facilities where water mist and vapour is created.


Pontiac fever does not require any treatment as patients recover from this disease spontaneously.

Legionnaires' disease is usually treated with antibiotics known as respiratory fluoroquinolones (such as levofloxacin) or macrolides. Treatment can be necessary for up to 3 weeks, and severe cases usually require hospitalization in an intensive care unit.


Where Does It Commonly Occur?

Legionnaires' disease occurs worldwide throughout the year but is more common in summer and autumn.