The intensive-care unit called me in to see a young patient who was admitted to the hospital earlier that day from the emergency room. She was 40 years old, relatively healthy, and had a medical history only of well-controlled hypertension and mild asthma. She felt ill for one week before visiting the ER with chest discomfort, cough with yellow sputum production, and generalized body aches.

In the ER, she was in respiratory distress with rapid breathing and heart rate, a temperature of 105.5 degrees Fahrenheit, and low oxygen saturation (the level of oxygen in the blood). She required use of a BIPAP machine — which is a noninvasive breathing machine to improve oxygen levels — as nasal oxygen alone was not adequate.

Her initial laboratory test results were quite concerning. She had elevated white blood cell count and blood lactic acid levels. This, combined with her vital signs and low oxygenation, meant that she had a serious infection affecting her vital functions. A chest X-ray showed she had a large, dense, right-sided pneumonia, an infection that inflames the air sacs in the lungs.

Blood cultures were immediately drawn, and she was started on antibiotics and intravenous fluids.

We considered the possible factors that could be causing her acute, severe illness. She did not smoke cigarettes or use illicit drugs, and she drank alcohol only on social occasions. She received her seasonal flu and pneumonia vaccines a month prior to being admitted to the hospital. She exercised daily and worked at a local restaurant as a server. She did not have any pets. She had not traveled recently and had never been abroad.

She was single and lived alone in her apartment in an old building in Philadelphia. She had long thought that the air in her bedroom was too dry, as it seemed to cause difficulty breathing, especially due to her mild asthma. Because of this, she used a humidifier every night in her room.

What was causing her severe pneumonia?


Within 24 hours of her admission to the hospital, we received her preliminary results to identify the cause of the pneumonia.

The lab reported positive Legionella antigen in her urine sample. Legionella is a bacteria that is a cause of atypical pneumonia, or “Legionnaires’ disease.” Symptoms of Legionnaires’ disease include cough, fevers, shortness of breath, muscle aches, and headaches. Occasionally, nausea, vomiting and diarrhea can occur. The bacteria also can cause a less severe illness called “Pontiac fever,” which is a mild upper-respiratory infection similar to influenza.

The Legionella bacteria is found in water and soil, especially in warm water when algae or organic matter are present. In the past, outbreaks of legionellosis were linked to hot tubs, central air-conditioning systems, cooling towers, large water systems, hot water tanks or decorative fountains. It also can be linked to household items, such as shower heads, faucets, humidifiers or respiratory therapy devices.

When water contaminated with Legionella is aerosolized into mist and inhaled into the lungs, it can cause pneumonia. Most people who get exposed to Legionella do not become ill, and the bacteria typically does not spread from person to person. While even healthy people can develop pneumonia, there usually are predisposing factors for infection, such as history of smoking, diabetes, cancer, lung disease, chronic kidney or liver disease or weakened immune systems.

Prevention of this infection occurs through good maintenance of water systems; large facilities should perform routine checks for the presence of this bacteria. Shower heads and faucets should be cleaned regularly. While there is no vaccine available for Legionella infection, it is treated by antibiotics.

Our patient reported she had a cool mist humidifier in her bedroom that she used daily for her asthma. It was never cleaned, and the filter was not changed. This was likely the source of her infection. Humidifiers should be cleaned daily and, instead of tap water, bottled, filtered or demineralized water should be used. Humidifier filters should be changed as recommended by the manufacturers, typically every two months.

Our patient recovered fully with antibiotics, supplemental oxygen, inhalers and IV fluids. After a brief stay in ICU, she was transferred to the regular medical floor and was discharged home three days later.

Legionella infection has a special history in Philadelphia. In 1976, the Convention of the American Legion was held at the Bellevue-Stratford Hotel in Philadelphia to coincide with the 200th anniversary of the signing of the Declaration of Independence. During the convention, an outbreak of pneumonia occurred, and, of the 2,000 attendees, more than 200 people fell ill and were hospitalized, resulting in 34 deaths. After an outbreak investigation led by the Centers for Disease Control and Prevention, a new bacteria was linked to the hotel’s air-conditioning system. In honor of the victims, the bacteria was named Legionella pneumophila, and the infection was called “Legionnaires’ disease.”

Gul Madison, M.D. is an infectious-disease specialist at Mercy Philadelphia Hospital.