Health Effects of legionellosis

Legionellosis is a respiratory infection caused by bacteria in the Genus Legionella. Currently, there are approximately 50 species of Legionella consisting of 70 serogroups, but Legionella pneumophila serogroup 1 is responsible for about 95% of the Legionnaires' Disease cases in U.S.

The severity of legionellosis (the disease caused by Legionella) varies from a mild fever (called Pontiac fever) to a more serious pneumonia (called Legionnaires’ disease) that can affect anyone, but principally affects those who are more susceptible due to age, illness, immunosuppression or other risk factors, such as smoking.

Water is the natural reservoir for Legionellae, and the bacteria are found worldwide in many different natural and manmade aquatic environments, such as cooling towers; water systems in hotels, homes, ships and factories; respiratory therapy equipment; fountains; misting devices; and spa pools. The greatest concern is where water is aerosolized into small droplets; for example with showers, humidifiers, fountains, etc.

Since 2000, legionellosis has been on the rise and approximately 5,000 cases of Legionella are reported each year in the United States , however, the exact incidence of disease is difficult to determine since the symptoms can be similar the common cold.


Who is at Risk?

Normal, healthy people are at low risk for contracting legionellosis, but the probability of infection increase in the elderly- particularly for men.  An infection is also typically associated with some other underlying factors including:

  • people over 45 years of age
  • smokers and heavy drinkers
  • people suffering from chronic respiratory or kidney disease, diabetes, lung and heart disease, renal or hepatic failure
  • systemic malignancy
  • immune system disorders
  • anyone with an impaired immune system



How do you contract Legionella?

Legionella is contracted when small droplets of water (aerosols), containing the bacteria, are suspended in the air and inhaled.  Certain conditions increase the risk from Legionella if:

  • The water temperature is between 20-45 °C, which is suitable for growth of the bacterium.
  • Fine mists of water are created.The droplet has to be small enough to travel deep within the lungs.
  • The water is stored, stagnant and/or re-circulated such that any disinfectant has been depleted.
  • Deposits (e.g. rust, sludge, scale) or slime films (called biofilms) are present to support bacterial growth providing a source of nutrients.

What are the Symptoms of Legionnaires’ and how is it treated?

The diagnosis of Legionnaires' disease can be delayed due to its similarities with the symptoms of the flu:

  • high temperature, feverishness and chills
  • cough
  • muscle pains
  • headache
  • pneumonia
  • diarrhea
  • signs of mental confusion

    Legionnaires’ disease is NOT spread from person to person. If you develop symptoms of legionellosis, you should contact your health care provider. The illness can be treated with antibiotics. Your doctor can order a urine or blood test which is helpful in deciding whether an illness is Legionnaires' disease. When doctors are aware that the illness is present in the local community, they have a much better chance of diagnosing it earlier.