Sunday, February, 12, 2012

Pneumonia - Introduction

Table of Contents

One of the most common causes of bacterial CAP is Streptococcus pneumoniae. Other causes include Haemophilus influenzae, mycoplasma, and Chlamydia.

Pneumonia Arising in an Institutional Setting

  • Hospital-Acquired Pneumonia. Hospital-acquired pneumonia is an infection of the lungs contracted during a hospital stay. This type of pneumonia tends to be more serious, because patients in the hospital already have weakened defense mechanisms, and the infecting organisms are usually more dangerous than those encountered in the community. Hospital patients are particularly vulnerable to Gram-negative bacteria and staphylococci. Hospital-acquired pneumonia is also called nosocomial pneumonia.
  • Ventilator-associated pneumonia (VAPP). A subgroup of hospital-acquired pneumonia is ventilator-associated pneumonia (VAP), a highly lethal form contracted by patients on ventilators in hospitals and long-term nursing facilities. Research finds that using endotracheal (breathing) tubes coated with silver might help to cut down on ventilator-associated pneumonia infections in the intensive care unit, because silver can kill bacteria and other microbes.
  • Nursing-home acquired pneumonia. Pneumonia acquired in a nursing home or other long-term care facility is the second most common type of infection in these facilities, usually bacterial. It is sometimes difficult to diagnose as older populations are less likely to report fever, chills, and chest pain. Chest radiography and physical exam are necessary. Sputum sample and antigen tests may be helpful.
Hospital-acquired pneumonia Click the icon to see an image of hospital-acquired pneumonia.

Disease Process Leading to Pneumonia

Pneumonia-causing agents reach the lungs through different routes:

  • In most cases, a person breathes in the infectious organism, which then travels through the airways to the lungs.
  • Sometimes, the normally harmless bacteria in the mouth, or on items placed in the mouth, can enter the lungs. This usually happens if the body's "gag reflex," an extreme throat contraction that keeps substances out of the lungs, is not working properly.
  • Infections can spread through the bloodstream from other organs to the lungs.

However, in normal situations, the airways protect the lungs from substances that can cause infection.

  • The nose filters out large particles.
  • If smaller particles pass through, nerves along the airway prompt a cough or sneeze. This forces many particles back out of the body.
  • Tiny particles that reach the small tubes in the lungs (bronchioles) are trapped in a thick, sticky substance called mucus. The mucus and particles are pushed up and out of the lungs by tiny hair-like cells called cilia, which beat like a drum. This action is called the "mucociliary escalator."
  • If bacteria or other infectious organisms manage to avoid the airway's defenses, the body's immune system attacks them. Large white blood cells called macrophages destroy the foreign particles.
Blood cells Click the icon to see an image of a macrophage.

Review Date: 04/13/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)