Is Legionnaires’ Disease Contagious and How is it Spread?

Legionnaires’ disease is a severe form of pneumonia that causes the inflammation of the lungs. Bacteria named as legionella is the causative organism of the disease. It spread through drinking water or from inhalation of air containing water droplets rich in legionella or contaminated soil. The symptoms of the disease are similar to flu and pneumonia. Old age, smoking, chronic lung disease, and weak immune system are the risk factors of the disease.

Is Legionnaires’ Disease Contagious and How is it Spread?

No, Legionnaires’ disease is not contagious. It means it does not spread from the infected person to others. It is a disease caused by a bacterium named Legionella. The bacteria thrive in water and soil. It lives in water sources such as ponds, river, swimming pools, hot springs, usually in low density and cannot cause infection. It can grow in indoor water systems like hot water tubes, mist sprayers or air conditioners. Sometimes, it can multiply in the artificial water system of home and industry.

Outbreaks of Legionnaires’ disease occur more commonly in summer season or in early autumn season. However, it can occur in any season in a year. Its outbreak is supported by the plumbing system of large buildings where legionella can grow, multiply and spread easily. It generally happens due to transmission in large water sources such as hot tubs and whirlpools in a cruise ship, swimming pools, and cooling towers of air conditioning systems, water fountains, grocery store mist machines and water systems in public places like hospitals, hotels or nursing homes. Transmission of Legionella bacteria is possible only by cooling systems of air conditioning where water is used for cooling. Home or car air conditioners do not use water for cooling.

The Mode Of Transmission Of Legionella Bacteria Is Possible By

Drinking Water- Drinking water from the water sources contaminated with Legionella can lead to the development of Legionnaires’ disease.

Inhalation- Inhalation of water droplets containing the bacteria from the cooling towers of air cooling systems or decorative foundations or other water sources can contaminate your lungs with the bacteria and can induce the disease.

Aspiration- Accidental aspiration of liquids that contain the causative bacteria, can infect the lungs and cause symptoms of Legionnaires’ disease.

Soil- Few people who work in garden or soil contaminated with the bacteria can contract Legionnaires’ disease.

Legionnaires’ disease is a life-threatening infection of lungs that can be a sporadic or local problem in hospitals and nursing homes. Here people are more vulnerable to the infection as the causative bacteria can easily spread in patients usually have weak immunity. Exposure to legionella bacteria does not means that every individual can catch the infection. There are certain factors that can risk you to contract the disease.

The Risk Factors That Can Lead To The Infection Of Lungs By Legionella Bacteria Are

Weakened Immune System- People who have a weakened immune system due to chronic diseases like diabetes, other lung infections, cancer or who are immunocompromised in diseases like HIV or AIDS can contract the infection easily. Those who are consuming certain medications such as corticosteroids or drugs that can prevent rejection of an organ after transplantation can contract the disease.

Smoking- Regular smoking can reduce the strength of the lungs to fight infection as it causes damage to the lungs. Those who smoke are at more risk to catch the infection by Legionella.

Old Age- People above the age of 50 years are more susceptible to catch the infection.


Legionnaires’ disease is a serious ailment of lungs caused by Legionella bacteria that can be fatal. It is not contagious. It spread through drinking water, contaminated water droplets in the air, and soil. Everyone who comes in contact with the bacteria does not contract the infection until the individual has risk factors discussed above.

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Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 22, 2018

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