Final Exam

describe what an agent is

• microorganism capable of producing an infectious disease

• must be present for infection to occur

describe what a host is

a person or animal that is susceptible to disease

describe what the environment is (epidemiologic triangle)

the domain in which disease causing agents may exist, survive, or originate

describe what the time is (epidemiologic triangle)

the time it takes for an infectious disease to run its natural course

what is infectivity

ability to cause infection

what is pathogenicity

the ability to cause clinical disease

capacity of an agent to cause active clinical disease in the infected host

what is virulence

degree of pathogenicity

severity of the disease after infection occurs

what is the iceberg concept of infection

the fact that active clinical disease (the tip of the iceberg) accounts for a relatively small proportion of hosts infections and exposures to disease agents

what is vertical disease transmission

from mother to child

what is horizontal - direct disease transmission

person to person transmission

skin to skin, exchange of bodily fluids, sneezing, coughing

what is horizontal - indirect disease transmission

person to person but via intermediary source

airborne, vector borne, vehicle borne

what is natural, active disease immunity

results from an infection by the agent

leads to antibody production in the host resulting in long lasting immunity

what is artificial, active disease immunity

results from an injection with a vaccine that stimulates antibody production in the host

long lasting immunity

what is natural, passive disease immunity

preformed antibodies are passes to the fetus during pregnancy and during breastfeeding

provides immediate, temporary protection to newborn

what is artificial, passive disease immunity

preformed antibodies are given to exposed individuals to confer protection against a disease

provides immediate, temporary protection

what is an asymptomatic carrier

individuals with inapparent infections

never develop an illness but can transit their infection to others

what is an incubatory carrier

people going to become ill but being transmitting their infection before their symptoms start

what is a convalescent carrier

people who continue to be infectious after their recover from illness

what is a chronic carrier

people who continue to harbor infections for a year or longer after their recovery

what is generation time

time interval between exposure to an infectious agent and the maximal infectivity of the host

what is incubation period

the time interval between exposure to an infectious agent and the appearance of the first signs and symptoms of disease

what is a point source curve

-persons are exposed to the same common source over a brief period

-majority of cases occur within one incubation period

what is a propagated source curve

-does not have common source but instead is caused by spread of infectious agent from one susceptible person to another

-transmission may occur directly or via an intermediate host

-multiple peaks separated by one incubation period

what is attack rate

the proportion of a group that experiences the outcome under study over a given period

what is secondary attack rate

an index of the spread of disease in a family, household, dwelling unit, dormitory or similar circumscribed group

measure of infectivity

what is case fatality rate

proportion formed by the number of deaths caused by a disease among those who have the disease during a time interval

what is basic reproductive rate

a measure of the number of infections produced on average by an infected individual in the early stages of an epidemic when virtually all contacts are susceptible

what is an index case

case that first comes to attention of public health authorities

what is a coprimaries case

cases related so closely in time that they are considered to belong to same generation of cases

what is an initial case

index case and coprimaries

what is a secondary case

person who becomes ill after a disease has been introduced into a population and who becomes infected from contact with a primary case

what are the steps to investigating an infectious disease outbreak

Step 1: establish the existence of an outbreak

Step 2: verify the diagnosis

Step 3: construct a working case definition

Step 4: find cases systematically and record information

Step 5: perform descriptive epidemiology

Step 6: develop hypothesis

Step 7: evaluate hypotheses epidemiologically

Step 8: reconsider, refine, and reevaluate hypothesis

Step 9: implement control and prevention measures

Step 10: communicate findings

what is a continuous common source curve

-exposure is not confined to one point in time

-last more that one incubation period

what is an intermittent source curve

-similar to continuous but exposure is intermittent

-multiple peaks

-no relation to the incubation period

what is the definition of screening

the presumptive identification of unrecognized disease or defects by the application of tests, examinations, or other procedures that can be applied rapidly

how is screening different from diagnosis

-used to detect potential disease indicators

-target large numbers of asymptomatic individuals

-simple and cheap

-results indicate suspicion of disease

when should we performs screening tests

• social

  • health problem should be important for the individual and community

  • diagnostic follow up and intervention should be available to all who require them

  • there should be a favorable cost benefit ration

  • high public acceptance

• scientific

  • natural history of the condition should be adequately understood

  • a knowledge base exists for the efficacy of prevention and the occurrence of side effects

  • prevalence of the disease or condition is high

• ethical

  • program can alter the natural history of the condition in a significant proportion of those screened

  • suitable, acceptable tests for screening and diagnosis of the condition as well as acceptable, effective methods of prevention are available

what are the characteristics of a good screening test

• simple

• rapid

• inexpensive

• safe

• acceptable

what is the interrelationship between reliability and validity in the evaluation of screening tests

• reliability

  • the ability of a measuring instrument to give consistent results on repeated trials

• validity

  • the ability of a measuring instrument to give a true

it is possible for a measure to be highly reliable but invalid

it is not possible for a measure to be valid but reliable

describe the interrelationship between specificity and sensitivity

• sensitivity

  • proportion of people who test positive among all those who actually have the disease

  • percentage of true positives

• specificity

  • proportion of people who test negative among all those who actually do not have that disease

  • percentage of true negatives

explain the procedures to improve the specificity or sensitivity of a screening test

to improve sensitivity, the cut point used to classify individuals as diseased should be moved towards the range of normal

to improve specificity, the cut point should be moved towards the range typically associated with the disease

• retrain screeners

• recalibrate screening instrument

• utilize a different test

• utilize more than one test

describe the sources of bias in screening

• lead time bias

  • the perception that the screen detected case has longer survival because the disease was identified early

• length bias

  • disease identified through screening has slower, less aggressive course and therefore better prognosis

• selection bias

  • motivated participants have a different probability of disease than do those who refuse to participate

explain how the predictive value of a screening can vary according to the prevalence of a disease

• prevalence of disease falls → predictive value (+) falls, and predictive value (-) rises

define environmental epidemiology

the study of disease and health conditions that are linked to environmental factors

what are some examples of recent environmental catastrophes that are associated with human health effects

love canal, respiratory illness from wildfires, heatstroke due to heat waves, waterborne diseases following floods

what is the healthy worker effect

observation that employed populations tend to have a lower mortality experience than the general population

explain the impact of the healthy worker effect on occupational morbidity and mortality

may reduce the measure of effect for an exposure that increases morbidity and mortality

define what hazard surveillance is

characterization of known chemical, physical, and biologic agents in the workplace

explain the purpose of hazard surveillance

to prevent injuries and illnesses before they occur

what is the concept of sentinel health event

case of unnecessary disease, unnecessary disability, or untimely death whose occurrence is a warning signal that the quality of preventative or medical care may need to improve

what are the methodological difficulties associated with research on environmental health effects

• studies may not adequately control for confounding factos

• long term effects of exposure are difficult to measure

• effects of low level exposures are difficult to demonstrate

• small study samples