HSC 400- Final Study Guide (5-8-16) PDF

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Epidemiology 400-Final Exam Review Sheet (Chapters 10, 11 and 12) Bring a calculator, number 2 pencil and scantran 882 1) Know what a confounder is and know the prevention strategies to control it. 

Confounder: The distortion of the estimate of the effect of an exposure of interest because it is mixed with the effect of an extraneous factor



Occurs when the crude and adjusted measures of effect are not equal (difference of at least 10%). Can be controlled for in the data analysis.



Be a risk factor for the disease.



Be associated with the exposure.



Not be an intermediate step in the causal path between exposure and disease.



Ways to control it o

Stratification--analyses performed to evaluate the effect of an exposure within strata (levels) of the confounder.

o

Multivariate techniques--use computers to construct mathematical models that describe simultaneously the influence of exposure and other factors that may be confounding the effect.

2) Internal and external validity 

Internal validity is when there is proper selection of the study groups and lack of error in measurement.



External validity is the ability to generalize beyond a set of observations to some universal statement.

3) Types of selective bias and information bias 

Selective Bias: Distortion that results from procedures used to select subjects (Ex: Healthy workers effect) o



Non-Response: No answers. (Ex: Iowa Women’s Health Study)

Information Bias: Result of measurement error in assessment of exposure and disease. o

Recall Bias: Better recall among case than among control

o

Interviewer Bias: Interviewer probes for exposure in case more than control.

o

Prevarication Bias: Participant has alterior motives.

4) Know what contributes to random error 

Random Error: Fluctuations around a true values of a perimeter because of sampling variability. 



False association between exposure and disease that arise from chance.

Factors that contribute to random error: 

Poor Precision: Study factor not measured sharply.



Sampling Error: Sample values differ from values of population.



Variability of Measurement: Lack of agreement in results from time to time reflects random error in the type of measurement procedure employed.

*Increasing sample size reduces all of these.

5) Criteria that must be considered before a decision is made to implement a screening program in a community. 

Social: o

The health problem should be important for the individual and the community.

o

Every screening much have a diagnostic follow-up and intervention should be available to all who require them.



o

There should be a favorable cost-benefit ratio.

o

Public acceptance must be high.

Scientific: o

Natural history of the condition should be adequately understood. 

This knowledge permits identification of early stages of disease and appropriate biologic markers of progression.



o

A knowledge base exists for the efficacy of prevention and the occurrence of side effects.

o

Prevalence of the disease or condition is high.

Ethical: o

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

o

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

6) Reason for a diagnostic test. 

To confirm what doctor is looking for (Ex. Shadow on mammogram)

7) Type of screenings: mass screening, multiphasic, selective, etc. 

Multiphasic o

Defined as the use of two or more screening tests together among large groups of people.

o

Information obtained on risk factor status, history of illness, and physiologic and health measurements.

o

Commonly used by employers and health maintenance organizations.



Mass: o



screening on a large scale of total population groups regardless of risk status.

Selective: o

Screens subsets of the population at high risk for disease.

o

More economical, and likely to yield more true cases.

o

Example: Screening high-risk persons for Tay-Sachs disease.

8) Conditions favorable to population screening for pre-symptomatic diagnosis of a given disease. 

Simple--easy to learn and perform.



Rapid--quick to administer; results available rapidly.



Inexpensive--good cost-benefit ratio.



Safe--no harm to participants.

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Acceptable--to target group.



Reliability types o

Repeated measurements: the degree of consistency among repeated measurements of the same individual on more than one occasion.

o

Internal consistency: evaluates the degree of agreement or homogeneity within a questionnaire measure of an attitude, personal characteristic, or psychological attribute.

o 

Interjudge: reliability assessments derived from agreement among trained experts.

Validity types o

Content: the degree to which the measurement incorporates the domain of the phenomenon under study.

o

Criterion-referenced: found by correlating a measure with an external criterion of the entity being assessed. 

Predictive Criterion-referenced Validity: denotes the ability of a measure to predict some attribute or characteristic in the future



Concurrent Criterion-referenced Validity: obtained by correlating a measure with an alternative measure of the same phenomenon taken at the same point in time.

o

Construct: degree to which the measurement agrees with the theoretical concept being investigated.

9) Sensitivity, specificity, reliability, validity, internal and external validity, content validity, construct validity, etc.



Sensitivity o

The ability of the test to identify correctly all screened individuals who actually have the disease (a/a+c).



Specificity o

The ability of the test to identify only nondiseased individuals who actually do not have the disease (d/b+d).



Predictive value (+) o



The proportion of individuals screened positive by the test who actually have the disease (a/a+b).

Predictive value (-) o

The proportion of individuals screened negative by the test who do not have the disease (d/c+d).

10) Know how to read targets of validity and reliability. It is possible for a measure to be reliable but invalid however it is not possible for a measure to be valid and unreliable

11) Know how to calculate sensitivity, specificity, predictive value (+) and (-), prevalence and accuracy. 

Sensitivity: a/ (a+c) x 100



Specificity: d/ (d+b) x 100



Predicative Value (+): a/ (a+b) x 100



Predictive Value (-): d/ (c+d) x 100



Prevalence: a+c / (a+b+c+d)



Accuracy: a+d/ (a+b+c+d)

12) Identify false positives, false negatives, true positives and true negatives.

13) Halo effect and social desirability effects on the validity of a questionnaire. 

Halo effect: The influence upon an observation of the observer’s perception of the characteristics of the individual observed. The influence of the observer’s recollection or knowledge of findings on a previous occasion. o

Example: a health care provider’s tendency to rate a patient’s sexual behavior use in a particular manner, based on a general opinion about a patient’s characteristics without obtaining specific information about past sexual behavior.



Social desirability: Respondent answers questions in a manner that agrees with desirable social norms. o

Example: Teenage boys might respond to a screening interview about sexual behavior by exaggerating their frequency of sexual activities because these behaviors might be perceived as socially desirable among some male peer groups.

14) Be familiar with arthropods, Q fever, Lyme disease, zoonoses, vectors, rabies and measles. 

Arthropods: Insect vectors that carry disease to humans. o



Ex: Ticks, fleas, Lyme disease.

Q Fever: Caused by a rickettsia. o

Rickettsia: Genius bacteria that grows within cells.



Lyme Disease: Tick-borne illness. (Caused by arthropod)



Zoonoses: Transmittable from vertebrae animals to humans. o

Ex: Rabies.



Vectors: Insect that carries agent.



Measles: Viral disease.

15) The difference between epidemic, endemic and pandemic. Also enzootic and epizootic.



Endemic: regularly found among specific people or area.



Pandemic: prevalent over a whole country or world



Epidemic: a widespread occurrence of an infectious disease in a community at a particular time like the flu.



Enzootic: is the non-human equivalent of endemic



Epizootic: is a disease that is temporarily prevalent and widespread in an animal population.

16) Vaccine preventable diseases. 

Vaccines are routinely given to children (0-6 years) for the prevention of several diseases, including:

o

Chickenpox, Diphtheria, Haemophilus influenzae type b infections, hepatitis A, hepatitis B, influenza, measles, meningococcal meningitis, mumps, pertussis, paralytic poliomyelitis, pneumococcal disease, rotaviral enteritis, rubella, and tetanus.

17) Pathogenicity, infectivity, virulence, resistance what are they and how do we measure them. 

Pathogenicity: Agent causes overt disease in host. o

Measured by ratio of number of individuals with clinically apparent disease to the number of exposed to infection.





Infectivity: Enter and multiply in host and produce infection. o

Polio, measles.

o

Measured by secondary attack rate.

Virulence: Agents capacity to induce disease in host. o

Measured by ratio formed by number of total cases with overt infection divided by the number of infected cases.



Toxigenicty: Capacity agent to produce toxins.



Resistance: Ability of agent to survive in bad environments.



Antigenicy: Ability of agent to induce antibody production in host.

18) Types of immunity (artificial, natural etc). 



Active Immunity: Disease organism stimulates potential hosts immune system to create antibodies. o

Natural, Active Immunity: Results from infection by agent.

o

Artificial, Active Immunity: Results from and injection.

Passive Immunity: Short-term provided by antibody. o

Natural, Passive Immunity: Antibodies given to fetus. Short-term.

o

Artificial, Passive Immunity: Preformed antibodies given to exposed individuals.

19) Physical environment factors in the natural history of disease 

The domain external to the host in which the agent may exist, survive, or originate.



The environment consists of physical, climatologic, biologic, social, and economic components that affect the survival of the agents and serve to bring the agent and host into contact.

20) Social environment factors in the natural history of the disease.

21) Portal of entry and exit of a disease.



Portal of exit—sites where infectious agent may leave the body, e.g., respiratory passages, the alimentary canal, and the openings in the genitourinary system, and skin lesions. o

Agent must exit in large enough quantities to survive in the environment and overcome the defenses at the portal of entry into the host.



Portal of entry--locus of access to the human body, e.g., mouth and digestive system and the mucous membranes or wounds in the skin.

22) Direct and indirect transmission of a disease. 

Direct would be person to person such as blood or bodily fluids.



Indirect would be getting infected by vectors, fomites, vehicles. o

Vehicles: contaminated water, food, infected blood on a needle.

o

Fomites: touching a doorknob

o

Vectors: mosquitos and flies

23) Know how to calculate attack rate. 



Attack Rate: Portion of group that experiences outcome over period of time. o

Similar to incidence rate.

o

Used when occurrence of disease raises over short period.

Formula: ill / ill + well x 100

24) Know the definition of case fatality rate and know the formula. 

Case Fatality Rate (CFR): Proportion formed by number of deaths by disease among those who have disease during a time interval.



Formula: # of deaths due to disease / # of cases of disease x 100

25) Fomites, generation time, herd immunity and incubation period. 

Fomite: objects or materials that are likely to carry infection, such as clothes, utensils, and furniture.



Generation Time: Time between lodgment of agent and maximal communicability.



Herd Immunity: Immunity of population against disease when large portion of individuals vaccinated.



Incubation Period: Time between exposure and symptoms. o

Applies to only clinically apparent diseases.

o

Useful for determining etiologic agent.

26) Food born illness pathogens such as salmonella.



One of the most common infectious disease problems in the community. Examples include: o

Staphylococcus aureus--present in contaminated food that have been stored at improper temperatures.

o

Trichinosis--associated with inadequately cooked pork products.

27) Measles vaccine outcome. 

Measles is preventable by vaccine given to children 0-6 years old

28) Small pox eradication. 

Small pox was eradicated in 1980.

29) Reason for resurgence of TB. 

By 2010, TB incidence had declined.



Most affected groups were foreign-born individuals and racial and ethnic minorities. Current high-risk populations o

Migrant farm workers

o

Homeless persons



Extensively drug-resistant tuberculosis (XDR TB) was the focus of media attention in 2007.



Increase in people infected with HIV, Increase in homeless population,

30) Know and define the factors that comprise the epidemiological triangle. 

Epidemiological Triangle: A model used to explain the etiology of infectious diseases. o



Recognizes three major factors in the pathogenesis of disease: agent, host, and environment.

The Epidemiologic Triangle is a model that scientists have developed for studying health problems. It can help your students understand infectious diseases and how they spread. and facts.



The Triangle has three corners (called vertices): o

Agent, or microbe that causes the disease (the “what” of the Triangle)

o

Host, or organism harboring the disease (the “who” of the Triangle)

o

Environment, or those external factors that cause or allow disease transmission (the “where” of the Triangle)

31) What kind of agent is Schistosomiasis? 

Schistosomiasis is caused by a Helminth agent.



Schistosomiasis is the infection caused by adult worms in the bloodstream. The cycle involves alternate human and snail hosts.

32) Inapparent infection, Colonization. 

Innapparent Infection: A subclinical infection that has not yet penetrated the clinical horizon--No symptoms of infection present. o

Important because disease can be transmitted to unsuspecting hosts.

o

In asymptomatic individuals, clinicians can look for serologic evidence of infection.

o

Example: Increase in antibodies and enzymes in patients with hepatitis A virus.



Colonization: Agents multiply on the surface of the body without invoking tissue or immune response.



Infestation: the presence of a living infectious agent on the body’s exterior surface, upon which a local reaction may be invoked....