Pneumonia

In addition to exposure to sufficient quantities of causative organisms, certain conditions may predispose an individual to pneumonia. Certainly, the lack of normal anatomical structure could result in an increased risk of pneumonia. For example, there are certain inherited defects of cilia which result in less effective protection. Cigarette smoke, inhaled directly by a smoker or second-hand by an innocent bystander, interferes significantly with ciliary function, as well as inhibiting macrophage function.

Stroke, seizures, alcohol, and various drugs interfere with the function of the epiglottis, leading to a leaky seal on the trap door, with possible contamination by swallowed substances and/or regurgitated stomach contents. Alcohol and drugs also interfere with the normal cough reflex, further decreasing the chance of clearing unwanted debris from the respiratory tract.

Viruses may interfere with ciliary function, allowing themselves or other microorganism invaders, such as bacteria, access to the lower respiratory tract. One of the most important viruses which in recent years has resulted in a huge increase in the incidence of pneumonia is HIV (Human Immunodeficiency Virus), the causative virus in AIDS (Acquired Immune Deficiency Syndrome). Because AIDS results in a general decreased effectiveness of many aspects of the host's immune system, a patient with AIDS is susceptible to all kinds of pneumonia, including some previously rare parasitic types which would be unable to cause illness in an individual possessing a normal immune system.

The elderly have a less effective mucociliary escalator, as well as changes in their immune system, all of which cause them to be more at risk for the development of pneumonia.

Various chronic conditions predispose to pneumonia, including asthma, cystic fibrosis, neuromuscular diseases which may interfere with the seal of the epiglottis, esophageal disorders which result in stomach contents passing upwards into the esophagus (increasing the risk of aspiration of those stomach contents with their resident bacteria), as well as diabetes, sickle cell anemia, lymphoma, leukemia, and emphysema.

Pneumonia is one of the most frequent infectious complications of all types of surgeries. Many drugs used during and after surgery may increase the risk of aspiration, impair the cough reflex, and cause a patient to underfill their lungs with air. Pain after surgery also discourages a patient from breathing deeply and coughing effectively.