Legionnaires’ disease risk spikes in the summer – what you need to know

Legionella pneumophila seen under a scanning-electron microscope. Image credit: CDC/ Margaret Williams, PhD; Claressa Lucas, PhD;Tatiana Travis, BS

This sometimes fatal pneumonia is often underdiagnosed by physicians

SUMMARY: Legionnaires’ disease is a bacterial disease that causes fever, cough, and pneumonia that can be seen on an x-ray. A milder form is called Pontiac Fever.

Legionnaires’ disease is a form of pneumonia that can be fatal in 1 out of 10 cases. Unfortunately, many doctors do not recognize the illness, so you need to be aware of signs and symptoms of the illness, especially if you are in a high-risk group or work in a setting where the illness is likely to occur.

History of Legionnaires’ disease and Pontiac Fever

Legionnaires’ disease and Pontiac fever are both caused by the bacterium Legionella pneumophila.

Legionnaires’ disease was so named an outbreak in 1976, when attendees of the Philadelphia convention of the American Legion got the lung infection. Pontiac Fever was first discovered in 1968 when people who worked at or had visited the Pontiac, Michigan city health department became ill.

It wasn’t until the bacterium Legionella was discovered after the 1976 Philadelphia outbreak that scientists were able to show that the same organism causes both illnesses.

Transmission of Legionella

Although you can get Legionnaires’ disease at any time of the year, significantly more cases occur in the summer and early fall.

People usually get infected with Legionella when they breathe in water vapor or mist contaminated with the bacteria. Common sources are steam from a whirlpool spa, fountains, and water from large water systems such as those in cruise ships, hotels, hospitals, and nursing homes.

It is important to note that the bacteria are not spread from person to person.


Legionnaire’s disease symptoms typically appear between 2 days to 2 weeks after exposure. The symptoms can range from mild to severe.

The main symptoms of Legionnaires’ disease are:

  • High fever
  • Cough
  • Chills

Less common symptoms:

  • Headache
  • Muscle pain
  • Abdominal pain
  • Chest pain
  • Shortness of breath

For Pontiac Fever, symptoms appear more quickly (usually 1 to 2 days after exposure to the bacteria) and typically go away with no treatment in a few days. Pontiac Fever feels like having the flu with the main symptoms of fever and muscle aches.

Risk factors

Legionnaires’ disease
Legionnaires’ disease usually impacts people over the age of 45, particularly smokers or people with a chronic lung disorder like asthma. According to the CDC, the following patients should be tested for

  • Patients who have had a failed course of antibiotics for community-acquired pneumonia
  • Patients with pneumonia so severe they are in intensive care
  • Any immunocompromised person with pneumonia
  • Any pneumonia patient who had traveled away from home within 10 days before falling ill
  • Patients with pneumonia who have been in the area of a Legionnaires’ disease outbreak
  • An at-risk patient who develops healthcare-associated pneumonia

Pontiac Fever
Pontiac Fever typically occurs in otherwise healthy people.

If you or a loved one gets ill with the symptoms above and have any of the risk factors, please discuss possible Legionella exposure with your doctor. For professionals who work in settings where Legionella is more likely to occur (such as a nursing home or hotel), we encourage you to be aware of the identification and reporting guidelines issued by the CDC.

To learn more about Legionnaires’ disease or Pontiac Fever, please refer to the comprehensive information provided by the Centers for Disease Control.

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