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What is Legionellosis?

Legionellosis is an infection caused by a type of bacteria called Legionella. Legionnaires' Disease refers to the more severe form of infection which includes pneumonia. The milder form of legionellosis is called Pontiac fever.  

 What are the symptoms of Legionellosis?

Symptoms of Legionnaires' Disease usually include fever, chills, and a cough. Some people also have muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea. People may also develop kidney problems and pneumonia. 

People with Pontiac fever experience fever and muscle aches but do not have pneumonia.

How long does it take for symptoms to develop?

Symptoms for people with Legionnaires' Disease can start 2 to 14 days after coming into contact with the bacteria. People with Pontiac fever start feeling sick within 24 to 48 hours after contact. 

 How is legionellosis spread?

This infection is spread when people breathe in a mist or vapor (small droplets of water in the air) containing the bacteria. People can get sick from breathing in droplets sprayed from a water system (such as cooling towers, hot water tanks, large plumbing systems or decorative fountains) that has not been properly cleaned and disinfected. The bacteria are not spread from one person to another person. There is no evidence that this bacteria grows in car or window air-conditioners.
How is it diagnosed?

If your healthcare provider suspects Legionellosis, he/she will order tests to confirm the presence of the bacteria. In Boston, suspect cases need to be reported to the Boston Public Health Commission at 617-534-5611.

How is legionellosis treated?

Antibiotics are used to treat people with Legionnaires' Disease. Treatment for Pontiac fever is supportive (fluids, rest fever reducing medicines).

 Who is at risk for developing Legionnaires' disease?

  • Older people (usually 50 years of age or older)
  • Current or former smokers
  • People with a chronic lung disease (such as COPD or emphysema)
  • People with a weakened immune system 

 What can be done to prevent legionellosis?

Proper maintenance of water systems can limit the growth of Legionella bacteria and spread of this infection. There are no vaccines that can prevent legionellosis.

During outbreaks, the Boston Public Health Commission identifies the source of the bacteria and recommends appropriate prevention and control measures. Recommendations may include decontamination of the water source.

 Legionnaires' diseasePontiac fever
SymptomsPneumonia, cough, fever; muscle aches, headache, tiredness, loss of appetite; occasionally diarrheaFlu-like illness (fever, chills, malaise) without pneumonia
Incubation period2-14 days after exposure24-72 hours after exposure
Etiologic agentLegionella speciesLegionella species
Case fatality rates5-30%0%


Boston Public Health Commission
1010 Massachusetts Ave, 6th Floor, Boston, MA 02118.
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