| An infection is defined as the presence and growth of a microorganism that produces tissue damage. Such microorganisms are called pathogens. The pathogen can be bacterial, viral, or fungal in nature. The extent of infection varies depending on the number of microorganisms, their ability to cause illness (virulence), and the body's ability to defend against them. Tissue damage can occur directly or from substances produced by the organism (e.g., toxins and enzymes). Localized infections affect one particular tissue or area of the body, whereas systemic infections affect the whole body.
Infections can be acquired in many different ways. Pathogens can be consumed (clostridium botulism, Salmonella) or inhaled (influenza virus, mycobacterium tuberculosis). In addition, some pathogens acquire access to the body by penetrating the skin or mucous membranes (Neisseria gonorrhoeae, HIV, bacteria that cause conjunctivitis). Sometimes organisms not usually harmful move from a part of the body where they normally exist to another part of the body where they can cause damage. For example, the bacteria E. coli is a normal inhabitant of the intestinal tract but causes serious illness if ingested or located in the urinary tract.
Many infections can spread from individual to individual in several ways. Airborne pathogens are discharged into the air from the respiratory tract of an infected individual through coughing or sneezing. They may be inhaled or settle on another individual, clothing, walls, or floors and then be transmitted by direct contact, which includes kissing and sharing utensils. Other pathogens can live on or in the bodies of individuals who do not experience symptoms but transmit the pathogens to others (carriers). Prenatal infection occurs when the mother passes an infection to her baby during pregnancy, either through the placenta or from contact with maternal membranes. Infections can also spread through insect vectors (such as mosquitoes or ticks), through animal carriers (by direct or indirect contact), on food (due to bacteria from the soil or from fertilizer), when soil enters the body through wounds (tetanus, gangrene), or through a contaminated water supply (typhoid, dysentery, or cholera).
Certain factors increase the risk of acquiring an infection, including injury (trauma), surgery, a defect in the body's natural defense system (immune compromise), and age.Risk: The very young and the elderly are at increased risk, compared to the rest of the population. |
Source: Medical Disability Advisor