Pathophysiology
Clinical meaning
Infectious diseases are caused by pathogenic microorganisms -- bacteria, viruses, fungi, and parasites -- that invade the body and multiply, triggering an immune response and producing clinical symptoms. Understanding the chain of infection is essential for the practical nurse to implement effective infection prevention and control measures. The six links in the chain are: the infectious agent (pathogen with sufficient virulence and number to cause disease), the reservoir (the habitat where the pathogen lives and reproduces -- human, animal, or environmental), the portal of exit (how the pathogen leaves the reservoir -- respiratory tract, GI tract, genitourinary tract, blood, skin), the mode of transmission (contact -- direct or indirect, droplet, airborne, vehicle, or vector), the portal of entry (how the pathogen enters a new susceptible host -- mucous membranes, respiratory tract, broken skin, parenteral route), and the susceptible host (factors determining host susceptibility include age, nutritional status, immune status, chronic disease, and invasive devices). Breaking any link in the chain prevents infection transmission. Healthcare-associated infections (HAIs) are a major patient safety concern, with the most common being catheter-associated urinary tract...