What is Legionnaires’ disease?

Legionnaires’ disease is a severe form of pneumonia caused by aspirating or inhaling small droplets of water contaminated with Legionella bacteria.

How soon after being exposed will a person develop symptoms of the disease?

Disease symptoms typically appear within 2-10 days of aspirating or inhaling contaminated water droplets. (+)

What are the symptoms of Legionnaires’ disease?

Early symptoms are much like the flu, and after a short time (often a day or two) more severe pneumonia-like symptoms may appear. Symptoms include fever, headache, aching joints and muscles, diarrhea, fatigue, loss of appetite, cough, difficulty breathing, shortness of breath, chills and chest pain.

Who has the highest risk of developing Legionnaires’ disease?

Some people have a lower resistance and are more likely to develop Legionnaires’ disease when exposed to Legionella bacteria. Those who have an increased risk are typically individuals over 50, smokers, those with a chronic lung disease such as emphysema or COPD, or are otherwise immunocompromised from diseases such as cancer, diabetes or kidney failure.

How is Legionnaires’ disease treated?

Legionnaires’ disease is most commonly treated with antibiotics. When treatment begins early after the onset of symptoms, the disease is treatable and most people recover. Consult your doctor with questions and at the first sign of symptoms.

How common is Legionnaires’ disease?

The CDC reports that there are approximately 5,000 cases each year in the United States. OSHA states that “It is estimated that over 25,000 cases of the illness occur each year” but most go unreported. A vast majority of cases, approximately 96 percent, are sporadic (single) cases and are not associated with a known outbreak.

Is there more than one strain of Legionella?

There are many species and serogroups of Legionella bacteria, with the most virulent strain being Legionella pneumophila Serogroup 1. Many strains have not been associated with the disease, which can often complicate efforts to test for the bacteria.

What is the most common source of Legionella bacteria?

According to the Centers for Disease Control and Prevention and peer-reviewed literature, the majority of Legionnaires’ disease cases are linked to the drinking water system. Drinking water systems that are not properly managed or treated supply Legionella bacteria to faucets, showerheads, humidifiers, ice machines, cooling systems and whirlpool spas. 

How can you test for Legionella?

There are several tests available. CDC’s Environmental Legionella Isolation Techniques Evaluation (ELITE) Program was created as a way for laboratories to test their Legionella isolation techniques against standardized samples. (+)  A list of laboratories that have met proficiency standards is available. (+)

Does Legionella bacteria also exist in the natural environment?

Yes, these bacteria are found in both natural and man-made water systems. Natural water sources— including streams, rivers, ponds, lakes, and mud—can contain Legionella in low levels. Once Legionella bacteria enters the public water system, it lives in the pipes’ biofilm where it multiplies.

What conditions are best for growth of Legionella bacteria?

Warm, stagnant water provides ideal conditions for growth. Legionella bacteria can multiply in water with temperatures between 68°-122°F (20°C-50°C). Temperatures between 90° and 105°F (32°C-40°C) are ideal for growth and proliferation of Legionella bacteria. Rust (iron), scale, and the presence of other microorganisms provide a perfect environment for Legionella to grow.  (+)

Can Legionnaires’ disease be prevented?

Yes, Legionnaires’ disease can be substantially prevented. According to the CDC, the primary way to prevent Legionnaires’ disease is stopping Legionella bacteria from entering the water supply and distribution systems in our homes and buildings.
Preventing Legionella and other water-borne threats requires the acknowledgement by public officials of the significant threats from our public water system, and a meaningful public discussion about the commitment required to upgrade and manage our public water system to ensure consistently clean and safe water. For example, the public water system infrastructure needs to be replaced in many cities where they are failing. Effective residual chlorine levels should be required through all points of the water distribution system. Special risk management protocols should be established to contain bacteria during system disruptions. Public notifications must be required during known and unknown disruptions. Lastly, comprehensive testing should be conducted to determine root causes and advance our understanding of bacterial threats.
Additional preventive steps can also be taken in our homes and the buildings that use water, including special handling following disruptions to the public water system, eliminating stagnant water, increasing water temperatures and developing water management programs as recommended by the CDC.

What can be done if a water system is already contaminated or is suspected of being contaminated?

Seek professional assistance before attempting to clean a contaminated water system and be sure to follow any applicable local, state or federal regulations in this area. The CDC has released a toolkit for investigating an outbreak. (+) Find more information here.

Why is it called Legionnaires’ disease?

Legionnaires’ disease got its name from the first recognized outbreak, which occurred in 1976 at a Philadelphia hotel where the Pennsylvania American Legion was having a convention. Over 200 Legionnaires and visitors at this convention developed pneumonia and some died. A newly discovered bacterium was found to be the cause of the pneumonia and was named Legionella pneumophila.

Can Legionella cause other diseases?

Yes. In addition to Legionnaires’ disease, the same bacteria also can cause a flu-like disease called Pontiac fever.

How does Pontiac fever differ from Legionnaires’ disease?

Pontiac fever produces flu-like symptoms that may include fever, headache, tiredness, loss of appetite, muscle and joint pain, chills, nausea, and a dry cough. Full recovery occurs in 2 to 5 days without antibiotics. No deaths have been reported from Pontiac fever.

Do we know everything about Legionnaires’ disease?

Like many diseases, scientists, epidemiologists, public health officials, and water quality specialists continue to study its causes and prevention. Much more research is necessary, particularly on transmission mode and Legionella bacteria detection and elimination technologies.