Image of a physician examining a lung x-ray, photo source: OSHA US Department of LaborLegionella bacteria, Legionnaire's disease testing & prevention

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Legionella hazards and HVAC equipment:

This article describes Legionella bacteria, Legionnaire's disease testing & prevention advice for building inspectors and owners. This is a chapter of our full document describing the inspection, maintenance, and repair of residential air conditioning systems (A/C systems) to inform home buyers, owners, and home inspectors of common cooling system defects. [

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

A Summary of Legionella sp. Health Concerns, Cooling Systems and Drinking Water

What are Legionella, Legionnaires' Disease, and Pontiac Fever?

Photograph of Legionella bacterium, provided by the U.S. Department of Labor, OSHA

Legionella, of which there are at least 40 species, include the species Legionella pneumophila which can cause infections in humans.

The name Legionella was derived from the discovery of this bacterium as the cause of infection of a significant of number of attendees at a convention of the American Legion in Philadelphia in 1976.

In that case the source of Legionella pneumophila was traced to the air conditioning system of the hotel where the convention was held.

Photographs courtesy U.S. Department of Labor, OSHA - see references below.] Also see Leaks, Rodents In Air Handlers and Mold Growth in Air Handlers as well as CONDENSATE DRIP TRAY DEFECTS.

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Where do Legionella sp. bacteria occur?

Legionella sp. bacteria occur naturally in the environment and are likely to be found in potable water supplies, especially those coming from bodies of water such as lakes and reservoirs.

Legionella bacteria are not likely to be removed by normal potable water treatment systems. In turn, potable water from a municipal supply is the typical source of water used in cooling towers.

Water from cooling towers or even aerosolized droplets of water from building plumbing fixtures (faucets and showers) or humidifiers or nebulizers may in turn spread Legionella bacteria to humans. Human infection by Legionella bacteria may take the form of Pontiac fever, or Legionellosis, which produces flu-like symptoms which can disappear after a few days.

More serious illness, Legionnaires' disease, is potentially fatal. Symptoms of Legionnaires' disease are typical of pneumonia in general and include high fever, dry cough, chills, and loss of appetite, headache, disorientation, and perhaps diarrhea or vomiting. In more advanced stages Legionnaires' disease can cause difficulty in breathing and chest pains. Legionnaires' disease is treated by antibiotics.

What is the Recommended Level for Legionella sp. Bacteria in Water?

The U.S. Environmental Protection Agency US EPA specifies a goal of zero microorganisms of Legionella sp. in potable water. (A MCLG or maximum contaminant level goal of zero). Legionella sp. bacteria can be removed from a water supply by heating methods including steam heating, ionization or possibly ozone treatment, UV light sterilization [which may not be reliable in all applications], use of strong disinfectant methods with chlorine, or copper-silver ionization treatment.

How and When Should We Inspect and Test for Legionella sp. Bacteria?

A component of the risk evaluation for any potential environmental concern in a building is the decision of how far to go in inspection and testing for hazardous materials, including evidence of Legionella sp. bacteria.

he level risk determines the appropriate level of inspection and testing. In turn, the level of risk is comprised of several factors: the known history of the building, the visual observation of building conditions, and the vulnerability or health fragility of building occupants.

Factors increasing the health risk of Legionella sp. for individuals includes identifying the "at risk" population. These include: people who are heavy smokers or drinkers, people who have health conditions that weaken or threaten the immune system or pose special risk of respiratory illness (chronic obstructive pulmonary disease or COPD, kidney disease, or cancers of the head or neck), people who are undergoing chemotherapy or taking immunosuppressant drugs (cancer patients, organ transplant recipients), and people who are hospitalized and require special respiratory assistance measures (intubation, respiratory therapy, nebulizers).

More about risk assessment in buildings and the decision process for hiring a professional for more thorough inspection and testing (pertinent to mold investigations) is at When to hire a professional.

Legionellosis: Legionnaires' Disease (LD) and Pontiac Fever - Information from the U.S. CDC

What is Legionnaires' disease?

Legionellosis is an infection caused by the bacterium Legionella pneumophila. The disease has two distinct forms:

Legionnaires' disease, the more severe form of infection which includes pneumonia, and Pontiac fever, a milder illness.

Legionnaires' disease acquired its name in 1976 when an outbreak of pneumonia occurred among persons attending a convention of the American Legion in Philadelphia. Later, the bacterium causing the illness was named Legionella.

Legionnaires' disease (LEE-juh-nares) is caused by a type of bacteria called Legionella. The bacteria got its name in 1976, when many people who went to a Philadelphia convention of the American Legion suffered from an outbreak of this disease, a type of pneumonia (lung infection).

Although this type of bacteria was around before1976, more illness from Legionnaires' disease is being detected now. This is because we are now looking for this disease whenever a patient has pneumonia.

Each year, between 8,000 and 18,000 people are hospitalized with Legionnaires' disease in the U.S. However, many infections are not diagnosed or reported, so this number may be higher. More illness is usually found in the summer and early fall, but it can happen any time of year.

What are the usual symptoms of legionellosis?

Legionnaires' disease can have symptoms like many other forms of pneumonia, so it can be hard to diagnose at first. Signs of the disease can include: a high fever, chills, and a cough. Some people may also suffer from muscle aches and headaches. Chest X-rays are needed to find the pneumonia caused by the bacteria, and other tests can be done on sputum (phlegm), as well as blood or urine to find evidence of the bacteria in the body.

These symptoms usually begin 2 to 14 days after being exposed to the bacteria.

A milder infection caused by the same type of Legionella bacteria is called Pontiac Fever. The symptoms of Pontiac Fever usually last for 2 to 5 days and may also include fever, headaches, and muscle aches; however, there is no pneumonia. Symptoms go away on their own without treatment and without causing further problems.

Pontiac Fever and Legionnaires' disease may also be called "Legionellosis" (LEE-juh-nuh-low-sis) separately or together.

How serious is Legionnaires' disease? What is the treatment for Legionnaires' disease?

Legionnaires' disease can be very serious and can cause death in up to 5% to 30% of cases. Most cases can be treated successfully with antibiotics [drugs that kill bacteria in the body], and healthy people usually recover from infection.

Where do Legionella bacteria come from?

The Legionella bacteria are found naturally in the environment, usually in water. The bacteria grow best in warm water, like the kind found in hot tubs, cooling towers, hot water tanks, large plumbing systems, or parts of the air-conditioning systems of large buildings. They do not seem to grow in car or window air-conditioners.

How do people get Legionnaires' disease?

People get Legionnaires' disease when they breathe in a mist or vapor (small droplets of water in the air) that has been contaminated with the bacteria. One example might be from breathing in the steam from a whirlpool spa that has not been properly cleaned and disinfected.

The bacteria are NOT spread from one person to another person.

Outbreaks are when two or more people become ill in the same place at about the same time, such as patients in hospitals. Hospital buildings have complex water systems, and many people in hospitals already have illnesses that increase their risk for Legionella infection.

Other outbreaks have been linked to aerosol sources in the community, or with cruise ships and hotels, with the most likely sources being whirlpool spas, cooling towers (air-conditioning units from large buildings), and water used for drinking and bathing.

Who gets Legionnaire's disease?

People most at risk of getting sick from the bacteria are older people (usually 65 years of age or older), as well as people who are smokers, or those who have a chronic lung disease (like emphysema).

People who have weak immune systems from diseases like cancer, diabetes, or kidney failure are also more likely to get sick from Legionella bacteria. People who take drugs to suppress (weaken) the immune system (like after a transplant operation or chemotherapy) are also at higher risk.

What should I do if I think I was exposed to Legionella bacteria?

Most people exposed to the bacteria do not become ill. If you have reason to believe you were exposed to the bacteria, talk to your doctor or local health department. Be sure to mention if you have traveled in the last two weeks.

A person diagnosed with Legionnaires' disease in the workplace is not a threat to others who share office space or other areas with him or her. However, if you believe that there your workplace was the source of the person's illness, contact your local health department.

Source Material Dated: October 12, 2005 Content source: Coordinating Center for Infectious Diseases / Division of Bacterial and Mycotic Diseases

Also see HOT WATER ANTI-SCALD REGULATIONS where we discuss methods for preventing Legionella formation in water heating equipment.

Legionella Information & Legionella-related Articles


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