The faulty gene that causes cystic fibrosis disrupts the normal flow of salt and water in and out of the lungs and other organs. This salt imbalance results in thick, sticky mucus that builds up in the lungs, allowing germs to thrive and multiply.

When the body's immune system (white blood cells) attacks the germs, the lungs become inflamed. This inflammation spurs the creation of more mucus, which then blocks the airways, and allows more germs to grow.

Dangerous Germs

Many germs are especially dangerous for people with CF and may lead to a faster decline in lung function. Studies show that people with CF are at particular risk of spreading certain germs among others with the disease. This is called cross‐infection.

Some of these germs include:

• Pseudomonas aeruginosa (P. aeruginosa) - Pseudomonas are common bacteria that come in thousands of different strains and are found in many different environments. Some strains have become resistant to multiple antibiotics and can be very hard to treat. Medical data show that people with CF may pick up these more difficult‐to‐treat strains of the bacteria from each other.
• Methicillin‐resistant Staphylococcus aureus (MRSA) - MRSA are strains of Staphylococcus aureus that are resistant to commonly used antibiotics. MRSA can be spread from one person to another through casual contact, like shaking hands, or by touching objects that have the bacteria on them.
• Burkholderia cepacia complex (B. cepacia) - This group of germs lives in damp or wet places and is often difficult to treat once it infects the lungs.
• Aspergillus - Aspergillus is a common mold (a type of fungus) found indoors and outside. It causes a disease called aspergillosis, which usually only develops in people with weakened immunity or lung disease.
• Nontuberculous mycobacteria (NTM) - This group of bacteria lives in soil, swamps, and water sources. NTM can survive many disinfectants and severe environmental conditions. The bacteria have been found in growing numbers of people with CF.
• Influenza, commonly called the flu, is a virus that is highly contagious, even among people who do not have CF. Every year in the United States, flu epidemics occur during the winter months. Although anyone can get the flu, people with CF can get much sicker. For people living with CF, getting the flu can lead to a severe lung infection. 

Despite significant progress treating cystic fibrosis, infections remain a serious problem and can lead to worsening lung disease or death. To learn more about research to develop new therapies, visit Research Into Infections.