Know the components in the CHAIN OF INFECTION
*Reservoir* Part 2: Chain of Infection
*A place where microorganisms survive, multiply, and await transfer to a susceptible host. To thrive organisms require a proper environment, including appropriate food, oxygen, water, temperature, pH, and light.* *Common Reservoirs* Humans (those w/ acute or symptomatic disease/those who show no signs of disease but are carriers of it are all HOSTS), animals (also hosts), insects, food, water, and organic matter on inanimate surfaces (fomites) *Frequent Reservoirs for Health Care Associated Infections (HAI* Health care workers, especially in their hands; patients; equipment; and the environment. *Food* Microorganisms require nourishment. Some such as Clostridum perfringens, the microbe that causes gas gangrene, thrive on organic matter. Others such as Others such as Escherichia coli consume undigested foodstuff in the bowel. Carbon dioxide and inorganic material such as soil provide nourishment for other organisms. *Oxygen* *Aerobic* bacteria require oxygen for survival and for multiplication sufficient to cause disease. Aerobic organisms cause more infections in humans than anaerobic organisms. Ex) Staphylococcus aureus. *Anaerobic* bacteria thrive where little or no free oxygen is available. Anaerobes typically cause infections deep within the pleural cavity, in a joint, or in a deep sinus tract. An example of an anaerobic organism is Bacteroides fragilis, an organism that is part of the normal flora of the human colon but can cause infection if displaced into the bloodstream or surrounding tissue following surgery or injury. *Water* Most organisms require water or moisture for survival. Ex) Frequent place for microorganisms is the moist drainage from a surgical wound. Some bacteria assume a form, called a spore, which is resistant to drying, and can live on inanimate surfaces for long periods of time. A common spore-forming bacterium is C. difficile, an organism that causes antibiotic-induced diarrhea. *Temperature* Microorganisms can live only in certain temperature ranges. Each species of bacteria has a specific temperature at which it grows best. The ideal temperature for most human pathogens is 20° to 43° C (68° to 109° F). For example, Legionella pneumophila grows best in water at 25° to 42° C (77° to 108° F). Cold temperatures tend to prevent growth and reproduction of bacteria (bacteriostasis). A temperature or chemical that destroys bacteria is bactericidal. *pH* The acidity of an environment determines the viability of microorganisms. Most microorganisms prefer an environment within a pH range of 5.0 to 7.0. Bacteria in particular thrive in urine with an alkaline pH. *Light* Microorganisms thrive in dark environments such as those under dressings and within body cavities.
*Portal of Exit* Part 3: Chain of Infection
*After microorganisms find a site to grow and multiply, they need to find a portal of exit if they are to enter another host and cause disease.* Ex.) Sites include: blood, skin and mucous membranes, respiratory tract, genitourinary (GU) tract, gastrointestinal tract (GI), and transplancental (mother to fetus). Some viruses such as Ebola virus are transmitted through direct contact with the blood or body fluids of a person who is sick with Ebola. However, droplets (e.g., splashes or sprays) of respiratory or other secretions from a person who is sick with Ebola could also be infectious. Therefore certain precautions (called standard, contact, and droplet precautions) are recommended for use in health care settings to prevent the transmission of the virus from patients who are sick with Ebola to health care personnel and other patients or family members *Skin and Mucous Membranes* The skin is considered a portal of exit because any break in the integrity of the skin and mucous membranes allows pathogens to exit the body. This may be exhibited by the presence of purulent drainage. *Respiratory Tract* Pathogens that infect the respiratory tract such as the influenza are released from the body when infected person sneeze or coughs. *Urinary Tract* Normally urine is sterile. However, when a patient has a urinary tract infection (UTI), microorganisms exit during urination. *Gastrointestinal Tract* The mouth is one of the most bacterially contaminated sites of the human body, but most of the organisms are normal floras. Organisms that are normal floras in one person can be pathogens in another. For example, organisms exit when a person expectorates saliva. In addition, gastrointestinal portals of exit include emesis, bowel elimination, drainage of bile via surgical wounds, or drainage tubes. *Reproductive Tract* Organisms such as Neisseria gonorrhea and HIV exit through a man's urethral meatus or a woman's vaginal canal during sexual contact. *Blood* The blood is normally a sterile body fluid; however, in the case of communicable diseases such as HBV, HCV, or HIV, it becomes a reservoir for pathogens. Organisms exit from wounds, venipuncture sites, hematemesis, and bloody stool.
*Mode of Transmission* Part 4: Chain of Infection
*Each disease has a specific mode of transmission. Many times you are able to do little about the infectious agent or the susceptible host; but, by practicing infection prevention and control techniques such as hand hygiene, you interrupt the mode of transmission.* Same microorganism sometimes transferred by more than one route. *Ex) Varicella zoster (chickenpox) is spread by airborne route in droplet nuclei or by direct contact. *Major route of transmission for pathogens: unwashed hands of the health care worker. *Equipment used within the environment (e.g., a stethoscope, blood pressure cuff, or bedside commode) often becomes a source for the transmission of pathogens.
*Infectious Agent* Part 1: Chain of Infection
*Microorganisms include bacteria, viruses, fungi, and protozoa.* *Microorganisms on the skin are either resident or transient flora.* *Resident microorganisms *(normal flora) are permanent residents of the skin and within the body, where they survive and multiply without causing illness. Resident skin microorganisms are not virulent (ability to produce disease). Can can cause skin serious infection when surgery or other invasive procedures allow them to enter deep tissues or when a patient is severely immunocompromised (impaired immune system). *Transient Microorganisms* Attach to the skin when a person has contact with another person or object during normal activities. Ex.) When you touch a contaminated gauze dressing or cleanse a patient following diarrheal episode, transient bacteria adhere to skin.
*Portal of Entry* Part 5: Chain of Infection
*Organisms enter the body through the same routes they use for exiting.* For example, during venipuncture when a needle pierces a patient's skin, organisms enter the body if proper skin preparation is not performed first. Factors such as a depressed immune system that reduce body defenses enhance the chances of pathogens entering the body.
*Host* Part 6: Chain of Infection
*Susceptibility* to an infectious agent depends on an individual's degree of resistance to pathogens. *Although everyone is constantly in contact with large numbers of microorganisms, an infection does not develop until an individual becomes susceptible to the strength and numbers of the microorganisms.* A person's natural defenses against infection and certain risk factors (e.g., age, nutritional status, presence of chronic disease, trauma, and smoking) affect susceptibility (resistance) Organisms such as S. aureus with resistance to key antibiotics are becoming more common in all health care settings, but especially acute care. The increased resistance is associated with the frequent and sometimes inappropriate use of antibiotics over the years in all settings (i.e., acute care, ambulatory care, clinics, and long-term care)
Chain of Infection
*The presence of a pathogen (disease causing microorganism) does not mean that an infection will occur. Infection occurs in a cycle that depends on the presence of all of the following elements:* 1) *An Infectious Agent or Pathogen* 2) *A Reservoir or Source for Pathogen Growth* 3) *A Port of Exit from Reservoir* 4) *A Mode of Transmission* 5) *Port of Entry to A Host* 6) *A Susceptible Host*
