Legionnaires' Disease and Pontiac Fever (Legionellosis) Facts
Legionnaires' disease causes a severe form of pneumonia.
- Legionnaires' disease is a serious illness causing a pneumonia that can be fatal.
- Pontiac fever is a self-limited, flu-like illness.
- In 2017, health departments reported about 7,500 cases of Legionnaires' disease in the U.S.
- Legionnaires' disease is spread by water vapor and droplets containing the Legionella bacteria.
- The bacteria responsible for Legionnaires' disease was first identified in 1976 during an outbreak at the American Legion convention in Philadelphia, Pa.
- Legionellosis refers to the two clinical entities caused by the bacteria of the genus Legionella (Legionnaires' disease and Pontiac fever).
What Is the History of Legionnaires' Disease and Pontiac Fever (Legionellosis)?
Legionnaires' disease and Pontiac fever are two diseases caused by the bacterium Legionella. This organism was identified in 1976 during an outbreak at the American Legion Convention in Philadelphia at the Bellevue-Stratford Hotel. Subsequently, the organism was also linked to an earlier flu-like disease outbreak in Pontiac, Mich. Legionellosis refers to these two clinical entities caused by the bacteria of the genus Legionella.
Legionnaires' disease causes a severe form of pneumonia that can be very serious and even fatal. It requires treatment with antibiotics and supportive care. Many people with Legionnaires' disease will require hospitalization, especially the elderly and patients who have chronic illnesses. Legionella pneumophila causes Legionnaires' disease.
Pontiac fever is a milder illness with flu-like symptoms (no pneumonia) that is self-limited and not known to cause any fatalities. Hospitalization is usually not necessary as basic supportive care (drinking plenty of fluids, acetaminophen [Tylenol] to lower the fever) is all that is necessary.
What Are Causes and Risk Factors of Legionnaires' Disease and Pontiac Fever (Legionellosis)?
Both Legionnaires' disease and Pontiac fever are caused by the Legionella bacterium. Not everyone exposed to the Legionella bacteria will get ill.
Risk factors to develop the disease are
- a weakened immune system (due to a disease, such as cancer or HIV/AIDS, or medications that suppress the immune system);
- chronic lung disease;
- age over 50; and
- chronic illnesses, such as diabetes, cancer, and kidney or liver failure.
Patients with the above risk factors tend to be at risk for other infections as well and need to be very alert to the onset of new signs or symptoms and especially illnesses with fever, along with additional symptoms such as weakness, confusion, and shortness of breath.
Traveling has been identified as an additional risk factor for contracting Legionnaires' disease. These cases have been linked to contaminated water supplies in hotels and cruise ships.
Are Legionnaires' Disease and Pontiac Fever (Legionellosis) Contagious? How Do They Spread?
Legionnaires' disease and Pontiac fever are usually spread via water vapor or droplets containing the bacteria. They are not spread from person to person. A number of different water sources have been identified as the origin of outbreaks over the last few years:
- Cooling towers and air-conditioning systems
- Swimming pools
- Improperly drained hot tubs and whirlpools
- Water systems in hospitals and nursing homes and hotels
Diligent cleaning and inspection (testing for the presence of bacteria) can prevent the spread of the disease from these sources.
Although this is the most common form to spread Legionnaires' disease and Pontiac fever, there are reports of people getting ill from contaminated soil.
What Are Symptoms and Signs of Legionnaires' Disease and Pontiac Fever (Legionellosis)?
The first symptoms of Legionnaires' disease are usually headache, muscle pains, fever, and chills. The symptoms worsen after 1-2 days and then may include
In severe forms or when left untreated, Legionnaires' disease can progress to respiratory failure, renal failure, and death. Patients hospitalized with Legionnaires' disease have a 10% mortality rate.
Pontiac fever symptoms start within 2-3 days of exposure and are much milder. The patient experiences fever, chills, and muscle aches. Pontiac fever tends to be self-limited and has no significant complications. The symptoms usually resolve within a week with no remaining effects.
What Is the Incubation Period for Legionnaires' Disease and Pontiac Fever?
Legionnaires' disease develops 2-14 days after exposure to the bacteria.
When Should Someone Seek Medical Care for Legionnaires' Disease or Pontiac Fever (Legionellosis)?
If you suspect you have Legionnaires' disease or pneumonia, you should seek medical care. Patients who have a weakened immune system (due to a disease or medications that suppress the immune system), smoke or have lung disease, have chronic illnesses such as diabetes, cancer, kidney and liver failure, or the elderly need to be especially diligent to report any symptoms to their health care provider.
What Specialists Treat Legionnaires' Disease and Pontiac Fever?
Patients with Legionnaires' disease and Pontiac fever will usually be treated by primary care doctors (internal medicine or family medicine). If admitted to the hospital, an infectious disease specialist might also be involved in the patient's care.
What Tests Diagnose Legionnaires' Disease and Pontiac Fever (Legionellosis)?
After a complete examination, including questions about your symptoms and signs, a doctor will recommend different tests depending on the severity of your illness and your symptoms and signs.
Blood tests and urine tests can be used to establish the diagnosis of Legionnaires' disease or Pontiac fever. Blood tests will also help establish the severity of the disease and if any other organs are affected.
A chest X-ray, which can show the extent of lung involvement, might be ordered.
Sputum samples can be collected if the patient has a productive cough.
Depending on the patient's additional symptoms, more tests might be ordered such as a CT of the brain (if there is significant confusion) or a lumbar puncture (to rule out meningitis).
Additional medical specialists can be consulted to help with the diagnosis and treatment options (for example, an infectious disease specialist or a pulmonologist, a doctor who specializes in the lungs).
What Are Treatments for Legionnaires' Disease and Pontiac Fever (Legionellosis)?
Legionnaires' disease needs to be treated with antibiotics. The sooner treatment is started the better the ultimate outcome.
Antibiotics of choice to treat Legionnaires' disease are the macrolides (especially azithromycin [Zithromax]) and quinolones (levofloxacin [Levaquin]). The ultimate decision on antibiotic choice needs to be made by a health care provider based on local data and test results (antibiotic sensitivity and resistance).
Pontiac fever does not require antibiotics. Supportive care that includes drinking plenty of fluids and taking acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) for fever is usually all that is required.
What Are Legionnaires' Disease and Pontiac Fever (Legionellosis) Complications?
What Is the Prognosis for Legionellosis?
Legionnaires' disease can lead to severe complications such as respiratory failure, septic shock, acute kidney failure, and death.
Many people who have Legionnaires' disease will end up being admitted to the hospital, especially patients who have the risk factors mentioned above, as they are at risk for complications and death.
Death occurs in 10% of symptomatic cases of Legionnaires' disease.
Pontiac fever is usually self-limiting with no significant complications and no reported fatalities.
Is It Possible to Prevent Legionnaires' Disease and Pontiac Fever (Legionellosis)?
Prevention requires cleaning of water systems where the organism could be found (pools, whirlpools, and large water and air-conditioning systems) as well as routine testing of systems for the presence of bacteria.
Early reporting of patients with Legionnaires' disease by health care providers can help alert the local health department to potential outbreaks.
Have There Been Recent Outbreaks of Legionnaires' Disease or Pontiac Fever (Legionellosis)?
The CDC and local health departments track and monitor outbreaks.
Recent outbreaks include a 2019 outbreak at the Sheraton Atlanta Hotel in downtown Atlanta, the 2015 Legionnaires' disease outbreak in New York City linked to water towers, and an outbreak in the California state prison system.
More information on legionellosis outbreaks can be found at the CDC.
Dooling, K.L., K.A. Toews, L.A. Hicks, et al. "Active Bacterial Core Surveillance for Legionellosis -- United States, 2011-2013." MMWR Morb Mortal Wkly Rep 64.42 (2015): 1190-1193.
United States. Centers for Disease Control and Prevention. "Legionella (Legionnaires' Disease and Pontiac Fever)." April 30, 2018. <http://www.cdc.gov/legionella/index.html>.