The Most Common Organisms in Cystic Fibrosis Lung Infections

Getting to Know Your Enemy

Lung damage caused by repeated respiratory infections is the leading cause of death for people with cystic fibrosis. Getting to know some of the infections you may face can help you prepare for the challenges ahead and plan strategies to minimize your risks. The following organisms don’t occur very often in healthy people, but they are especially troublesome for those with CF.


Aspergillus is a fungus that occurs commonly in the environment, so it is difficult if not impossible to avoid coming in contact with. For most people, Aspergillus is harmless but for 15 percent of the people who have cystic fibrosis, it can lead to a life-threatening condition called allergic bronchopulmonary aspergillosis (ABPA).

In this case, you will have Aspergillus in the mucus in your lungs but it is not invasive. Instead, it triggers an excessive immune reaction with both antibodies and immune cells, causing an eosinophilic pneumonia. Symptoms include a cough with dirty green or brown flecks in your sputum. You will have asthma-like symptoms of wheezing and airway obstruction. In severe cases, you may also have fever, headache, and loss of appetite. It's diagnosed by a skin prick test for Aspergillus antigen and blood tests for Aspergillus precipitins and IgE antibodies and a chest X-ray or CT.

Treatment is with oral prednisone as inhaled corticosteroids don't work well for ABPA. If ABPA persists, you may be treated with an antifungal drug. Patients are followed with chest X-rays, pulmonary function tests, and lab tests as lung damage may continue to occur without a change in the symptoms. There is a risk of a permanent widening of the central airways, known as bronchiectasis, and scarring of the lungs.

Pseudomonas aeruginosa

More than half of all people with cystic fibrosis will battle a lung infection caused by the bacteria Pseudomonas aeruginosa at some point in their lives. In fact, it is the most commonly occurring organism in CF-related lung infections. Thus, P. aeruginosa is also the bacteria responsible for the death of many people with CF.

P. aeruginosa is a common bacteria found all around us in the soil, sinks, showers, and other moist environments, so it can't be avoided. It is hard to get rid of when it invades the respiratory tract.

An inhaled form of the antibiotic tobramycin, known as TOBI, is used to treat chronic Pseudomonas infections in people with cystic fibrosis. A dry powder TOBI Podhaler has also been developed.

Burkholderia cepacia

Burkholderia cepacia, which used to be called Pseudomonas cepacia, is a rare but significant threat to people who have cystic fibrosis. While the odds are in your favor that you'll never encounter Burkholderia cepacia, you should have a basic understanding of what it is and how to reduce your risk of getting it.

While it is in the environment, the strains that infect people are now shown to be spread from person to person. It can colonize the lungs and cause an infection that slowly deteriorates lung function. It can also spread throughout the body causing cepacia syndrome with rapid deterioration of the lungs. This can lead to death. It is treated with combination therapy as it can be resistant to most antibiotics.


Methicillin-resistant Staphylococcus aureus (MRSA), is becoming an increasingly common complication in people with cystic fibrosis. MRSA can be found on the skin, in wounds, in urine, and many other parts of the body but the lungs are the most common site of MRSA infection in those with CF.

MRSA is spread through direct and indirect contact and can be acquired in the community or in the hospital. Practicing good infection control can help reduce the risk.


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Ortega VE. Allergic Bronchopulmonary Aspergillosis (ABPA). Merck Manual Professional Version.

Ramphal R. Infections Due to Pseudomonas Species and Related Organisms. In: Kasper D, Fauci A, Hauser S, Longo D, Jameson J, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 19e. New York, NY: McGraw-Hill; 2015.