Legionnaires' disease

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at February 27, 2016
StartLegionnaires' disease

Legionnaires’ disease is a potentially life-threatening form of pneumonia. The disease is caused by inhaling the Legionella bacteria. The same bacteria are also responsible for a milder form of legionellosis called Pontiac fever, which resembles a mild case of the flu.


Definition & Facts

Approximately 8,000 to 18,000 people are hospitalized with Legionnaires’ each year in the United States. The disease was first discovered in 1976 after a number of people attending an American Legion convention in Philadelphia become sick with an unusual type of pneumonia.

Legionnaires’ disease cannot be spread by person-to-person contact. It is the direct result of inhaling the bacteria and less commonly of drinking contaminated water. Many of those exposed to the bacteria do not become sick. Those most likely to develop severe infections include:

Sporadic outbreaks of Legionnaires’ are common in hospitals and nursing homes where people are most vulnerable to infection and germs are spread easily.

Symptoms & Complaints

Symptoms of Legionnaires’ typically appear two to 10 days following exposure to the Legionella bacteria. Early symptoms may include muscle aches, headache, chills, and a high grade fever. Symptoms can progress rapidly. By the second to third day, most patients will experience:

Although Legionnaires’ is primarily a respiratory condition, it has been known to cause wound and heart infections. The milder form of the disease, Pontiac fever, does not cause pneumonia and typically resolves within five days.

Anyone suspecting they have been exposed to the Legionella bacteria or who experience the above symptoms should see their doctor immediately. Prompt treatment with the proper antibiotics can shorten the recovery time and prevent serious complications, including respiratory failure, septic shock, acute kidney failure, or even death.


Most cases of Legionnaires’ disease are caused by the bacteria Legionella pneumophila. These bacteria occur naturally outdoors in water and soil where it rarely causes infections. Indoors, the bacteria thrive in water systems such as air conditioners, hot tubs, and mist sprayers found in grocery store produce departments.

Most outbreaks of Legionnaires’ have occurred in large buildings, such as hotels and hospitals. This is most likely because the complex plumbing and ventilation systems in these buildings allow the bacteria to spread and grow easily. Most people become infected after inhaling aerosolized water droplets that contain the bacteria. Drinking contaminated water can also cause Legionnaires' disease. The Flint water crisis in Flint, Michigan resulted in an outbreak of Legionnaires' that has killed ten people.

Frequent sources of Legionnaires’ outbreaks include air conditioning cooling towers, plumbing systems, decorative fountains, swimming pools, whirlpools, and hot tubs. A person can also develop Legionnaires’ after aspirating, or choking, on water containing the bacteria, which allows the bacteria to enter directly into the lungs. In rare cases, people have contracted Legionnaires’ through contaminated soil.

Diagnosis & Tests

Legionnaires’ can be difficult to diagnose since the symptoms are similar to other types of pneumonia, and it can look identical on a chest X-ray. If an X-ray confirms pneumonia, the physician may order additional tests to check for the presence of Legionella bacteria and antigens. These tests include urine tests, blood tests, and sputum samples. If the patient is exhibiting neurological symptoms, such as confusion, the doctor may also order a brain CT scan or spinal tap to rule out other conditions.

Patient history is also an important part of diagnosing Legionnaires’ disease. The doctor will be alert to the possibility of exposure if the patient works in buildings or around equipment that are frequent sources for the bacteria or if there have been other confirmed cases of Legionnaires’ in the area.

Treatment & Therapy

Most cases of Legionnaires’ can be successfully treated with antibiotics. The most effective antibiotics in treating the condition include azithromycin, ciprofloxacin, levofloxacin, trovofloxacin, gemifloxacin, and moxifloxacin. Other agents, including trimethoprim, sulfamethoxazole, minocycline, doxycycline, and tetracycline, are also highly effective. The sooner antibiotic therapy is started, the better the patient’s chances of recovery.

In most cases, patients with Legionnaires’ will experience a complete recovery within a year. Many of these patients continue to experience fatigue, difficulty concentrating, weakness, and loss of energy for several months following hospitalization. Some patients also experience continued shortness of breath and coughing; however, it is not clear whether this is due to severe pneumonia in general or Legionnaires’ specifically.

Cigarette smokers are strongly encouraged to stop smoking following Legionnaires’ disease. Approximately 10 percent of those infected with Legionnaires’ will die as the result of complications from the disease. Those at greatest risk for complications are those who already suffer from weakened immune systems or who do not seek prompt treatment. Pontiac fever, the milder form of the condition, typically resolves without medical treatment. Antibiotics have not proven to be beneficial in treating Pontiac fever.

Prevention & Prophylaxis

Outbreaks of Legionnaires’ disease can be prevented through proper cleaning, disinfecting, and maintenance of spas, pools, plumbing systems, decorative fountains, cooling towers, and other water supplies. The high temperatures found in hot tubs can make it especially difficult to maintain the disinfectant levels necessary to kill Legionella and other types of bacteria. It is important to follow manufacturer, state, and local authority guidelines regarding the maintenance and disinfection of this equipment.

In other types of water supplies, hyperchlorination does not appear to be effective in controlling the Legionella bacteria. Newer methods of controlling and eliminating the bacteria include super heating, monochloramine disinfection, and copper-silver ionization. The Centers for Disease Control have also published detailed guidelines regarding the prevention of Legionnaires’ in hospitals.

During active Legionnaires’ outbreaks, health department officials work to identify the source of transmission so that appropriate decontamination and remediation measures can be implemented. Experts are also working on improving the design of plumbing systems and cooling towers to make it more difficult for the bacteria to colonize and become aerosolized.