Some groups of people are more susceptible to pneumonia. The elderly, infants, and young children are at highest risk.
Elderly people tend to have diminished cough and gag reflexes and weaker immune systems.
The immature immune systems and narrow airways of infants and young children make them more likely to develop pneumonia.
Another susceptible group consists of people with immune system disorders such as AIDS, or people who are taking medications that lower their immune response. People who have received organ or tissue transplants fall into this category.
People who are hospitalized are also at a higher risk for pneumonia. About five to 10 out of every 1000 hospitalized patients contract pneumonia every year.
Patients in the intensive care unit on mechanical ventilators are especially susceptible. Their risk of pneumonia can be significantly reduced with antibiotics.
Cigarette smoking, or being exposed to cigarette smoke, also increases the risk of pneumonia. Cigarette smoke can injure airways and damage the small hairs that act as filters in the nose and upper airway, called cilia. Toxic fumes, industrial smoke, and other air pollutants may also damage cilia function.