perplexed lungs with question marks against a split background of flames and germs

Staphylococcus Aureus and Decreased Lung Function in Cystic Fibrosis

Cystic fibrosis (CF) is caused by a defective protein. This protein affects how salt and water move in and out of cells. This leads to thickened mucus throughout the body. While CF affects the whole body, the lungs are the most common source of health problems.1,2

Lung damage

For people with CF, thick mucus clogs the airways. This allows bacteria to invade the lungs. Too much harmful bacteria can directly damage the lungs.3

The body reacts to bacteria by sending immune cells to the lungs. Immune cells work by releasing substances that destroy the bacteria. This immune activity causes inflammation, which can damage lung tissue even in people who don't have CF.3

Ongoing lung infections are linked to a long-term decrease in lung function. This decrease can lead to respiratory failure, when your lungs are not able to get enough oxygen into your blood. Over half of the deaths in people with CF are caused by lung complications.4-7

Testing for infection

Bacterial cultures are one way to test for a lung infection. To perform this test, doctors collect a sample of the mucus (also called sputum) from the lungs. The bacteria in the sample are then grown in the lab until they can be counted.4

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Many different bacteria are found in cultures from people with CF. The specific types of bacteria in the lungs are different for each person and change over time.2,8-10

The 2 most common types of bacteria found in people with CF are:2,8-10

  • Staphylococcus aureus (also called "staph")
  • Pseudomonas (P.) aeruginosa

Staph is the most common bacteria to cause infection in younger people with CF. About 8 out of 10 teens with CF have staph bacteria growing on or inside them. As people age, P. aeruginosa becomes more common. Across all age groups, about 3 out of 10 people with CF have ongoing staph infections.2,8-11

Staph infection results in more severe inflammation and lung damage than many other bacteria. Repeated infections are linked to worse performance on lung function tests and decreased lung function over time.7,12

Antibiotic resistance

Treating infections in people with CF is challenging. Staph bacteria can adapt to the environment inside the lung. This helps them survive treatment with antibiotics.3,7

An even more harmful type of staph is called methicillin-resistant Staphylococcus aureus (MRSA). MRSA is resistant to many antibiotics. It is found in 1 out of 4 people with CF in the United States. MRSA is linked to more severe illness and worse outcomes for people with CF.2,6,8-10,13

People with MRSA tend to have:8,8,13

  • Worse lung function
  • More hospital stays
  • Increased risk of death


There is a bill in Congress called the Pioneering Antimicrobial Subscriptions To End Upsurging Resistance (or PASTEUR) Act. This bill aims to address the problem of antibiotic resistance. If passed, it would provide funding to:14

  • Develop antibiotics to combat resistant bacteria
  • Fight against antibiotic resistance
  • Identify infections in need of new antibiotics

Symptoms of infection

If you or someone you care for has symptoms of infection, call your CF care team to discuss your treatment plan.1

Signs of infection include:15

  • Increased cough
  • Worsening difficulty breathing
  • Fever

Treatment options and preventing infections

Treatment of lung infections is different for each person. Your CF care team will tailor a treatment plan that is best for your unique situation. Antibiotics are a normal part of treatment.1

Basic infection prevention practices can help reduce your risk of infection:16

  • Stay at least 6 feet away from others with CF and anyone with a cold, flu, or infection.
  • Wash your hands regularly.
  • Cover your cough.
  • Clean and disinfect your nebulizer.
  • Do not share personal items like straws, utensils, towels, or nebulizers.
  • At the gym, sanitize and cover surfaces (with a towel) on the equipment you touch.
  • Stay up-to-date on vaccinations.

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