Symptoms of Legionnaires’ disease

Legionnaires’ disease is a lung infection that is commonly caused by bacteria of the legionella species. This is a serious condition which, if not treated promptly, may lead to death.

The bacteria commonly multiples and spreads in water works and air conditioning systems of large buildings. It naturally lives in natural water sources, soil and mud.

Legionellosis is a term that includes pneumonia like in Legionnaires’ disease as well as similar but less serious conditions of Pontiac fever.

When do symptoms of Legionnaires’ disease begin?

The symptoms of Legionnaire’s disease may begin any time from two to 19 days after inhaling tiny droplets of water contaminated with the bacteria. This period is called the incubation period.

The most common duration of the incubation period is 6 to 7 days. Attack rates of Legionnaires’ disease are 0.1 to 5% of the general population and 0.4–14% in hospitals.

Symptoms of the initial phase of Legionnaires’ disease

The initial phase lasts around 2 days where the patient usually complains of muscle pain, body aches and headaches. Thereafter the symptoms worsen.

Later symptoms of Legionnaires’ disease

There is high fever with temperature of 38ºC (100.4ºF) or above with chills and flu like features, severe muscle pain, tremendous fatigue, confusion etc.

Central nervous system features like confusion and delirium may be seen in nearly half of the affected individuals.

Other symptoms include feeling nauseous, vomiting, diarrhoea and loss of appetite. Diarrhea is seen in 25–50% of cases and vomiting and nausea in 10–30% of cases. There may be a general weakness.

As the bacteria affects the lungs there are symptoms like persistent cough that is dry initially but progresses to a more productive form where the patient coughs up mucus or even rarely blood.

Cough occurs in around 90% patients and coughing up mucus or blood in around a third of the affected cases. Patient suffers from shortness of breath and chest pains.

Pontiac fever – the other form of Legionnaires’ disease

There is another form of Legionellosis called the Pontiac fever or the “non-pneumonic legionellosis. This is more common and the bacteria possess a higher attack rate when populations are exposed.

The incubation period is shorter and is usually 1-2 days. The disease is a flu like syndrome with muscle pain, headache and fever. Around 50% develop cough.

The disease usually resolves by itself without too many complications. These infections are commonly missed during diagnosis because of their mild nature. Both Legionnaire’s disease as well as Pontiac fever begin similarly with flu like features.

Diagnosis of Legionnaires’ disease

Diagnosis of Legionnaires’ disease is usually made by blood or urine tests and by identification of the bacteria in the sputum and secretions of the respiratory tract.

Chest X-rays are advised and in Legionnaire’s disease these often are similar to pneumonia due to other causes. This makes diagnosis with X rays alone difficult. Chest X-rays show progression of fluid accumulation around the lungs.

The blood, sputum and urine tests are usually diagnostic. On staining the sputum sample with special dyes called Gram stain there may be numerous neutrophils.

In addition, there are features of kidney failure, severely low blood levels of Sodium, raised levels of enzyme Lactate dehydrogenase levels (>700 units/ml) and a general failure to respond to standard beta-lactam antibiotics like Penicillins or aminoglycoside antibiotics.

If untreated, Legionnaires’ disease usually worsens during the first week and can be fatal. Complications may include shock, kidney or respiratory failure (shut down) and multi-organ failure. (1-6)

Further Reading

Last Updated: May 27, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Mandal, Ananya. (2023, May 27). Symptoms of Legionnaires’ disease. News-Medical. Retrieved on June 01, 2023 from

  • MLA

    Mandal, Ananya. "Symptoms of Legionnaires’ disease". News-Medical. 01 June 2023. <>.

  • Chicago

    Mandal, Ananya. "Symptoms of Legionnaires’ disease". News-Medical. (accessed June 01, 2023).

  • Harvard

    Mandal, Ananya. 2023. Symptoms of Legionnaires’ disease. News-Medical, viewed 01 June 2023,


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment