The continuity of the lung airways with the external environment exacts a high level of risk for infection compared to other body organs. Bacteria, fungi and viruses can infect the upper and lower airways or the air sacs. Similar symptoms may occur with different causes of lung infections. Establishing an accurate diagnosis enables initiation of appropriate antimicrobial therapy.
Influenza
Influenza viruses cause the illness commonly known as the flu. The viruses typically invade the lining tissues of the throat and upper airways of the lungs. In some people, influenza viral infection extends into the air sacs, causing pneumonia. Viral infection of the air sacs damages the cells and provokes fluid leakage into the air spaces, limiting oxygen and carbon dioxide gas exchange. Shortness of breath and cough with phlegm production result. The Centers for Disease Control and Prevention reports more than 200,000 hospitalizations of American adults and children occur annually due to influenza-related illness.
Respiratory Syncytial Virus Infections
Respiratory syncytial virus, or RSV, commonly causes lung infections, especially among infants and young children. Lung infections associated with RSV include croup, bronchitis, bronchiolitis and pneumonia. According to data collected by the Centers for Disease Control and Prevention, approximately 25 to 40 percent of infants and young children who contract RSV develop pneumonia or bronchiolitis, an infection of the small airways leading to the air sacs. Adults most at risk for severe RSV lung infections include those with a weakened immune system or chronic disease, and people taking immunosuppressive medications.
Pneumococcal Pneumonia
The bacterium Streptococcus pneumoniae commonly causes pneumonia. The Centers for Disease Control and Prevention estimates pneumococcal infections cause approximately 50 percent of hospital-acquired adult pneumonias and 36 percent of community-acquired disease. Pneumococcus also causes a significant proportion of pneumonia cases among children. Fatal outcomes associated with pneumococcal pneumonia range from 5 to 7 percent, overall.
Tuberculosis
Infection with the bacterium Mycobacterium tuberculosis may lead to active pulmonary tuberculosis. Drs. Jatin Vyas and David Dugdale, III explain in a Medline Plus Medical Encyclopedia entry that infants, the elderly and those with decreased immune system function are at greatest risk for the development of active pulmonary tuberculosis. Data from the World Health Organization indicates that approximately 11.1 million people worldwide had active tuberculosis in 2008.
Blastomycosis
Blastomycosis is a fungal infection of the lungs caused by Blastomyces dermatitidis. The fungus most commonly occurs in the soil of the Midwest, Southeast and south central United States. Inhalation of Blastomyces dermatitidis spores from disturbed soil may lead to a fungal pneumonia.
References
- National Heart, Lung and Blood Institute: What Causes Pneumonia?
- University of Maryland Medical Center: Pneumonia, Causes
- American Lung Association: Influenza and Pneumonia
- Centers for Disease Control and Prevention: Flu Symptoms and Severity
- Centers for Disease Control and Prevention: Respiratory Syncytial Virus Infection, Clinical Description and Diagnosis
