Important words and concepts from Chapter 15, Black, 1999 (3/28/2003):

by Stephen T. Abedon ( for Micro 509 at the Ohio State University



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Vocabulary words are found below



(1) Chapter title: Epidemiology and Nosocomial Infections

(a)                    "People with infectious diseases are members of a population; they acquire infectious diseases and transmit them within a population. Therefore, to further our understanding of such diseases, we must consider their effects on populations, including hospital populations."

(b)                    [epidemiology and nosocomial infections (Google Search)] [index]

(2) Epidemiology

(a)                    "The study of factors and mechanisms involved in the frequency and spread of diseases and other health-related problems within populations of humans, other animals, or plants."

(b)                    Typically, if the cause of a disease is unknown, one approach to discovering its cause employs epidemiology (a second, parallel approach might include more traditional laboratory microbiological techniques)

(c)                    [epidemiology and "infectious disease" (Google Search)] [index]

(3) Etiology

(a)                    The (or a) cause, here particularly with reference to infectious diseases

(b)                    Etiologies are causes of specific diseases, e.g., HIV is the etiology (or etiological agent) of AIDS

(c)                    [etiology and "infectious disease" (Google Search)] [index]

(4) Incidence

(a)                    The incidence of a disease is the number of new cases that occur within a given period of time

(b)                    Typically incidence is expressed in units of per year per 100,000 people

(c)                    Measurement of the incidence of disease gives a direct indication of how quickly a disease is spreading within a population

(d)                    [incidence and "infectious disease" (Google Search)] [index]

(5) Prevalence

(a)                    Related to but not identical to the concept of incidence is prevalence

(b)                    Prevalence is the absolute number of cases present within a population at a given instance or over a period of time

(c)                    The prevalence differs from incidence particularly in including both old and new cases

(d)                    Prevalence indicates to what extent a disease is impacting on a population since it measures both the number of people affected and is affected by how long people are affected

(e)                    See Figure 15.1, Incidence and prevalence of rates

(f)                      [prevalence and "infectious disease" (Google Search)] [index]

(6) Endemic

(a)                    A disease that is endemic is continually present within a population

(b)                    Typically the disease agent is present in too-low concentrations to affect a large number of individuals (i.e., prevalence is low)

(c)                    See Figure 15.2, The incidence rate of chickenpox in the United States

(d)                    [endemic infectious disease (Google Search)] [index]

(7) Epidemic

(a)                    An epidemic refers to a higher-than-normal incidence of a disease within a population

(b)                    That is, the number of cases of the disease is increasing

(c)                    An epidemic may or may not be caused by an endemic disease

(d)                    [epidemic infectious disease (Google Search)] [index]

(8) Pandemic

(a)                    A world-wide epidemic is called a pandemic

(b)                    For example, HIV infection is (or, at least, was) considered to be a pandemic as it was increasing in incidence world-wide (and continues to do so in many parts of the world)

(c)                    [pandemic infectious disease, pandemic disease, pandemic influenza, pandemic HIV (Google Search)] [index]

(9) Sporadic

(a)                    A disease that is not endemic and only randomly and unpredictably present in a population is termed sporadic

(b)                    See Figure 15.3, The incidence of St. Louis encephalitis in the United States

(c)                    See Figure 15.6, Incidence rates of three different types of encephalitis

(d)                    [sporadic infectious disease (Google Search)] [index]

(10) Common-source outbreak

(a)                    A common-source outbreak is an epidemic that arises from contact with a contaminated substance, such as a contaminated water source

(b)                    The typically defining feature of a common-source outbreak is a lack of passage of the infectious agent from person to person, at least among the secondary carriers

(c)                    Typhoid Mary, on the other hand, represented a common source for the outbreak of typhoid fever she brought on by, though a carrier, insisting on handling and distributing food to the public

(d)                    [common-source outbreak, campylobacter, ciguatera, gastroenteritis, hepatitis, legionnaire (Google Search)] [index]

(11) Propagated epidemic

(a)                    In contrast to a common-source outbreak, a propagated epidemic has numerous infectious foci, i.e., infected people

(b)                    [propagated epidemic (Google Search)] [index]

(12) Index case

(a)                    The index case is the first identified case of an epidemic disease

(b)                    ["index case" and "infectious disease" (Google Search)] [index]

(13) Reservoirs of infection

(a)                    "Sites in which organisms can persist and maintain their ability to infect are essential for new human infections to occur. Such sites are called reservoirs of infection."

(b)                    Reservoirs of infection can be both animate (e.g., humans and other animals) and inanimate (e.g., soil and water)

(c)                    By far the most important reservoir of human infections is our fellow humans

(d)                    [reservoirs of infection (Google Search)] [ProMED-mail (reporting on emerging infectious diseases)] [index]

(14) Carriers

(a)                    Human reservoirs of infection that fail to show significant outward signs of infection are termed carriers

(b)                    Carriers may also be termed chronic where a chronic carrier continues to serve as a reservoir even after apparent recovery from a disease

(c)                    [carriers of infection (Google Search)] [index]

(15) Zoonoses

(a)                    Zoonoses are diseases with animal reservoirs of infection

(b)                    Generally, the more similar an animal is to us (i.e., the more closely related evolutionarily), the more likely they will be able to serve as a reservoir for a human disease, as well, of course, to being susceptible to human diseases (note that our pets should also be included among the "us" serving as reservoirs of diseases affecting wild animals)

(c)                    Nevertheless, rabies is our most important zoonosis due to its severity as well as its prevalence in wild- animal populations, plus our potential for coming into contact with the disease via our pets; the best way to contain the incidence of rabies among humans is the vaccination of pets against rabies virus

(d)                    Note that the more animal species a disease is endemic among and the greater its prevalence in the wild, the more difficult it is to eradicate the disease; our few successes against human diseases are against ones that have had etiologies that uniquely infect humans (e.g., smallpox, polio)

(e)                    See Table 15.1, Selected zoonoses (with emphasis on those that occur in pets)

(f)                      [zoonoses (Google Search)] [infectious diseases (author unknown)] [index]

(16) Portals of entry

(a)                    For a disease to successful infect us and cause disease, it must enter our body and then find its way to a location that it is capable of adhering to and then growing (alternatively, the pathogen-produced toxin, e.g., in the case of food poisoning, must successfully enter our bodies)

(b)                    The route through which the pathogen (or its toxin) enters our bodies is called its portal of entry

(c)                    Pathogens typically have well-defined portals of entry and are not infectious if they enter a different portal of entry

(d)                    Typically we possess defences against successful entry via a given portal of entry

(e)                    See Figure 15.9, Portals of entry for human pathogens

(f)                      Note that portals of entry include the various normally present openings into the body (e.g., mouth, ears, nose, eyes, urethra, etc.) as well as abnormal entries (e.g., broken skin, insect bites, surgical wounds) as well as the bridge between a mother and a fetus (the placenta, with pathogens usually passing from the mother to the fetus rather than the other way around); some parasites are even capable of passing through unbroken skin

(g)                    For organisms that can enter through more than one portal, the virulence of an infection can vary with portal of infection (e.g., Yersinia pestis and bubonic versus pneumonic plague)

(h)                    Often, but not always, the characteristics of a disease give reasonably good clues as to its portal of entry (e.g., respiratory infection) as well as its portal of exit

(i)                      [portals of entry (Google Search)] [index]

(17) Portal of exit

(a)                    Pathogens typically exit from animals in body fluids including saliva, respiratory fluids, feces, semen, vaginal secretions, urine, and blood

(b)                    As with portals of entry, different pathogens typically have their own distinctive portals of exit such that different diseases are spread through the contact with different body fluids

(c)                    See Figure15.10, Portals of exit for human pathogens

(d)                    [portals of exit (Google Search)] [index]

(18) Modes of transmission

(a)                    There exist a variety of modes of transmission

(i)                      Contact transmission

·        Direct contact transmission

·        Indirect contact transmission

·        Droplet transmission

(ii)                    Vehicle transmission

·        Waterborne transmission

·        Airborne transmission (including dust particles)

·        Foodborne transmission

(iii)                   Vector transmission

·        Mechanical vector

·        Biological vector

(b)                    See Figure 15.11, Modes of disease transmission

(c)                    ["modes of transmission" infectious disease (Google Search)] [index]

(19) Horizontal transmission

(a)                    Transmission of a pathogen can be either horizontal or vertical

(b)                    Horizontal means transmission between individuals specifically who are not related as a parent is to its offspring

(c)                    [horizontal transmission (Google Search)] [index]

(20) Vertical transmission

(a)                    Vertical transmission occurs from parent to offspring, e.g., in utero, during passage down the birth canal, or in breast milk

(b)                    Typically pathogens that have evolved for vertical transmission cannot be as virulent as those that have evolved for horizontal transfer since the recipient of the transfer must survive until reproductive maturity to pass on the pathogen

(c)                    However, note that not all (nor even most) pathogens that may be transmitted vertically have evolved for that mode of transmission (so, just as hybridomas and monoclonal antibodies typically are not made by employing recombinant DNA technology, don't leave this discussion thinking that all pathogens that may be passed from parent to offspring are harmless--most are instead just in the wrong place at the wrong time so far as the poor baby is concerned)

(d)                    [vertical transmission (Google Search)] [index]

(21) Contact transmission

(a)                    Contact transmission requires either the direct or indirect contact with a reservoir of infection

(b)                    ["contact transmission" and disease (Google Search)] [index]

(22) Direct contact transmission

(a)                    Direct contact transmission requires direct contact between individuals

(b)                    [direct contact transmission (Google Search)] [index]

(23) Direct fecal-oral transmission

(a)                    Direct fecal-oral transmission is an example of direct contact transmission where inappropriate hygiene (or kinky sexual practices) result in the direct contact between an individual and another individual's feces

(b)                    Fecal-oral contact can also occur via indirect routes as discussed below

(c)                    Fecal-oral contact, direct or not, is how pathogens with oral portals of entry and fecal portals of exit (many gastrointestinal diseases) get passed from individual to individual

(d)                    [direct "fecal-oral", fecal-oral (Google Search)] [index]

(24) Indirect contact transmission

(a)                    Indirect contact transmission does not involve direct contact between individuals

(b)                    Instead, contact is made between a healthy individual and the disembodied body fluid of a carrier (or diseased individual)

(c)                    [indirect contact transmission (Google Search)] [index]

(25) Fomites

(a)                    Indirect contact transmission typically occurs via fomites which are inanimate objects upon which a pathogen has been deposited

(b)                    Indirect contact transmission occurs via contact between a healthy individual and a pathogen-carrying fomite

(c)                    E.g., bed sheets, eating utensils, etc., just about any inanimate object a person can come into contact with can serve as a fomite, though some fomites serve as less hostile environments for the pathogen than others

(d)                    Note that fomites are not vehicles of transmission and that vehicles of transmission are not fomites

(e)                    [fomites (Google Search)] [CDC hospital infections program: laundry] [index]

(26) Droplet transmission

(a)                    Also among contact transmission is droplet transmission which are the droplets of respiratory fluids that are projected out of one's mouth or nose when one coughs, sneezes, or talks

(b)                    Pathogens with respiratory portals of exit often are transmitted by droplets

(c)                    Note that droplets have a finite life span and droplet transmission is considered to have occurred only if the droplet is contacted within one meter of its ejection from the ejecting individual

(d)                    [droplet transmission (Google Search)] [index]

(27) Vehicles

(a)                    A vehicle is a substance that is normally brought into the body, i.e., water, air, and food

(b)                    Pathogens hitch rides on (in) vehicles as a means of entering a body through a portal of entry

(c)                    Note that fomites are not vehicles of transmission and that vehicles of transmission are not fomites

(d)                    [vehicle transmission of disease (Google Search)] [index]

(28) Waterborne transmission

(a)                    Many, especially pathogens with anal portals of exit, may contaminate water and thereby become transmitted via waterborne transmission (and would be described as indirect fecal-oral transmission)

(b)                    Note that different pathogens display differences in their ability to survive in aqueous environments

(c)                    The prevalence of coliform bacteria (as well as coliphages) is often employed as an indicator of fecal contamination

(d)                    [waterborne transmission of disease (Google Search)] [index]

(29) Airborne transmission

(a)                    Air, especially dry air exposed to sunshine, is a hostile environment for many pathogens

(b)                    Nevertheless, some airborne transmission can occur

(c)                    Pathogens are said to be airborne if they travel more than one meter through air

(d)                    [airborne transmission of disease (Google Search)] [index]

(30) Foodborne transmission

(a)                    Foodborne transmission, like waterborne transmission, is usually of gastrointestinal pathogens

(b)                    [foodborne transmission of disease (Google Search)] [index]

(31) Isolation

(a)                    Disease transmission may be controlled by the isolation of individuals harboring a pathogen (e.g., in a hospital setting)

(b)                    Procedures necessary to effect successful isolation vary with the pathogen/disease

(c)                    Some isolation procedures are employed even when individuals are not known to harbor a pathogen (e.g., universal precautions)

(d)                    See Table 15.2, A summary of important isolation procedures

(e)                    [isolation and nosocomial (Google Search)] [recommendations for isolation precautions in hospitals (Guidelines for Isolation Precautions in Hospitals)]

(32) Quarantine

(a)                    Quarantines are used to limit the movement of individuals or populations who either harbor a/the pathogen or have been exposed to individuals known or thought to harbor a/the pathogen

(b)                    [quarantine (Google Search)] [index]

(33) Nosocomial infections

(a)                    A nosocomial infection is an infection that is acquired in a medical setting in the course of medial treatment

(b)                    In the U.S. 2 million people acquire nosocomial infections each year and 20,000 die of them

(c)                    [nosocomial infection, nosocomial disease (Google Search)] [index]

(34) Sources of nosocomial infections

(a)                    Nosocomial infections can come from either exogenous or endogenous sources

(b)                    [sources of nosocomial infection (Google Search)] [doorknobs: a source of nosocomial infection? (“This hospital study is a reminder of the often ignored fact that brass is bactericidal, while stainless steel is not”) (Copper and the Environment)] [index]

(35) Endogenous infections

(a)                    Endogenous infections are ones caused by opportunistic pathogens that come from a patient's own normal flora

(b)                    [endogenous infections (Google Search)] [index]

(36) Compromised hosts

(a)                    Endogenous infections may be acquired due to

(i)                      Patients being immunologically depressed

(ii)                    As a consequence of a loss of microbial antagonism due to antibiotic treatment

(iii)                   In the course of an invasive procedure

(iv)                  Due to injury

(b)                    ["compromised hosts" and disease (Google Search)] [index]

(37) Exogenous infections

(a)                    Exogenous infections come from sources outside of the patient's own body

(b)                    Compromised hosts also play a role in the occurrence of exogenous infections

(c)                    However, a fourth factor in exogenous infections is the presence within hospitals of pathogens that are particularly capable of infecting individuals in possession of the above risk factors (i.e., compromised hosts)

(d)                    Many of these pathogens possess antibiotic resistance

(e)                    Such hospital-specific pathogens can be found incorporated among the normal flora of staff or on fomites

(f)                      Much effort in a medical setting must be put forth to not only reduce patient contact with these pathogens but also to prevent these pathogens from becoming endemic to the hospital (e.g., passed around from patient to patient or found integrated in the normal flora of staff)

(g)                    [exogenous infections (Google Search)] [index]

(38) Modes of transmission of nosocomial infections

(a)                    "Direct person-to-person (contact) transmission between an infected patient, staff member, or visitor and noninfected patients; indirect (contact) transmission through equipment, supplies, and hospital procedures; and (vehicle) transmission through air are most common in hospitals." (people, stuff, and air)

(b)                    See Figure 15.20, Some common modes of transmission of nosocomial infections in a hospital setting

(c)                    See Figure 15.22, Relative frequencies of sites of nosocomial infections

(d)                    Organisms of particular concern include Escherichia coli, Enterococcus, Staphylococcus aureus, Pseudomonas

(e)                    ["modes of transmission" and nosocomial (Google Search)] [index]

(39) Universal precautions

(a)                    As a means of guarding against the transmission of blood-borne pathogens procedural guidelines, termed universal precautions, are applied in the handling of all patients

(b)                    Particular blood-borne pathogens of concern include HIV and hepatitis B virus (as pictured to the right)

(c)                    Body fluids except feces, nasal secretions, sputum, sweat, tears, urine, and vomit must be handled as though they are infectious with blood-borne pathogens (unless any of the above visibly contain blood), i.e., normal body secretions (except from the genitals area) are not covered under universal precautions

(d)                    In short, body fluids that in reasonable likelihood can contain blood-borne pathogens are treated differently from body fluids that have a low likelihood of containing blood-borne pathogens

(e)                    The universal precaution guidelines can be found in Appendix D (p. A26) of your text

(f)                      Basically,

(i)                      you should not be bringing or causing to bring body fluids from patients into your bodies, plus proactively preventing this from occurring

(ii)                    you should use barriers between you and body fluids

(iii)                   you should immediately and thoroughly wash any part of your body that has come into contact with these fluids

(g)                    See Table 15.5, some important universal precautions and recommendations from CDC

(h)                    [universal precautions (Google Search)] [index]

(40) Preventing nosocomial infections

(a)                    "Hand washing is the single most important technique" normally applied to the prevention of nosocomial infections; this inhibits both the spread of pathogens from patients to patients (or patients to fomites) but also from patients to staff as well as from staff to patients

(b)                    Staff should wash their hands with soap and water between patients

(c)                    One should take great care to employ aseptic techniques (constantly monitoring oneself for sloppiness)

(d)                    One should take great care in maintaining the sterility of equipment

(e)                    One should employ barriers (e.g., gloves) to prevent colonizing oneself with potential pathogens that come from fomites or patients

(f)                      [preventing nosocomial infections (Google Search)] [index]

(41) Vocabulary [index]

(a)                    Airborne transmission

(b)                    Carriers

(c)                    Common-source outbreak

(d)                    Compromised hosts

(e)                    Contact transmission

(f)                      Direct contact transmission

(g)                    Direct fecal-oral transmission

(h)                    Droplet transmission

(i)                      Endemic

(j)                      Endogenous infections

(k)                    Epidemic

(l)                      Epidemiology

(m)                  Etiology

(n)                    Exogenous infections

(o)                    Fomites

(p)                    Foodborne transmission

(q)                    Horizontal transmission

(r)                     Incidence

(s)                     Index case

(t)                      Indirect contact transmission

(u)                    Isolation

(v)                    Modes of transmission

(w)                  Modes of transmission of nosocomial infections

(x)                    Nosocomial infections

(y)                    Pandemic

(z)                     Portal of exit

(aa)                 Portals of entry

(bb)                Prevalence

(cc)                 Preventing nosocomial infections

(dd)                Propagated epidemic

(ee)                 Quarantine

(ff)                    Reservoirs of infection

(gg)                 Sources of nosocomial infections

(hh)                 Sporadic

(ii)                     Universal precautions

(jj)                    Vehicles

(kk)                Vertical transmission

(ll)                     Waterborne transmission

(mm)             Zoonoses