CHAIN of INFECTION Disease

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Infectious CHAIN OF INFECTION Disease For an infection to develop, Susceptible Reservoir Host each link of the chain must be connected. Breaking any link of the chain Portal of Portal of Entry Exit can stop the transmission of infection! Mode of Transmission INFECTIOUS DISEASE Any microorganism that can cause a disease such as a bacterium, virus, parasite, or fungus. Reasons that the organism will cause an infection are virulence (ability to multiply and grow), invasiveness (ability to enter tissue), and pathogenicity (ability to cause disease). RESERVOIR The place where the microorganism resides, thrives, and reproduces, i.e., food, water, toilet seat, elevator buttons, human feces, respiratory secretions. PORTAL OF EXIT The place where the organism leaves the reservoir, such as the respiratory tract (nose, mouth), intestinal tract (rectum), urinary tract, or blood and other body fluids. MODE OF TRANSMISSION The means by which an organism transfers from one carrier to another by either direct transmission (direct contact between infectious host and susceptible host) or indirect transmission (which involves an intermediate carrier like an environmental surface or piece of medical equipment). PORTAL OF ENTRY The opening where an infectious disease enters the host’s body such as mucus membranes, open wounds, or tubes inserted in body cavities like urinary catheters or feeding tubes. SUSCEPTIBLE HOST The person who is at risk for developing an infection from the disease. Several factors make a person more susceptible to disease including age (young people and elderly people generally are more at risk), underlying chronic diseases such as diabetes or asthma, conditions that weaken the immune system like HIV, certain types of medications, invasive devices like feeding tubes, and malnutrition. Summer 2011 .

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Commentary Disease Transmission Dynamics and the Evolution
Proc. Natl. Acad. Sci. USA Vol. 96, pp. 800–801, February 1999 Commentary Disease transmission dynamics and the evolution of antibiotic resistance in hospitals and communal settings Simon A. Levin*† and Viggo Andreasen‡ *Department of Ecology and Evolutionary Biology, Eno Hall, Princeton University, Princeton NJ 08544; and ‡Department of Mathematics, Roskilde University, DK-4000 Roskilde, Denmark Despite the tremendous benefits of antibiotics for dealing with sally, exercising little influence on their host under normal a wide range of pathogens, there is by now little doubt that conditions. Antibiotics are typically introduced to treat the their indiscriminate use has led to the emergence of novel true pathogens, and for them the problem of resistance resistant strains and a frightening new set of threats to public introduces questions concerning the length and intensity of health. Hospitals and other community settings provide an treatment, multidrug strategies, and patient compliance. (See, especially fertile ground for the spread of those types; in for example, refs. 2–4). Commensals provide a different sort particular, the recent emergence and proliferation of bacteria of problem, however. Under normal conditions, they live in resistant to both methicillin and vancomycin has engendered such places as the skin or upper respiratory tract, causing little serious concern, threatening the effectiveness of the last or no harm. On occasion, however, they become translocated available options for treatment of potentially fatal Staphylo- to sites that are normally sterile, such as the blood or lungs, coccus strains. where they may have serious harmful effects (6). Many viru- It seems clear that a considered and comprehensive strategy lence factors, for example in Staphylococcus aureus, are carried for antibiotic use is essential, permitting the intelligent de- on plasmids, and can be exchanged among different strains.
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