Review slides Flashcards by Jonathan Robinson

Surveillance. Think what 2 things?

Surveillance

Prevalence

Incidence rate

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Prevalence is a _ of a population at a given point in time

Incidence is a _ of a population at a given point in time

Prevalence is a measure of the state of a population at a given point in time

Incidence is a measure of events of a population at a given point in time

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Cumulative incidence is the _ of new cases that develop in a population _

equation?

Cumulative incidence is the proportion (risk) of new cases that develop in a population over time

CI = Pr(New Disease) = risk of disease = (# new cases)/ pop at risk….. over time t

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Incidence rate is the instantaneous or _

It is not a _ or _

equation?

Incidence rate is the instantaneous or average rate of disease occurrence

It is not a probability or proportion

IR=Rate of disease= (# cases)/(Persons at risk * time) or (sum of person time from follow up)

person time

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RR equation

RR= P(D+, E+)/ P(D+/E-).. over time t

RR= CI exposed/ CI unexposed.. over time t

CI exposed= (cases w/ exposure)/(person w/ exposure at risk)

CI unexposed=(cases w/o exposure)/(persons w/o exposure at risk)

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Risk difference eqt

I1-I0

Incidence among exposed- incidence among unexposed

the exposure is associated with a _% absolute increase in risk, compared to the unexposed group

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Incidence rate ratio eqt

IRR= (rate of disease in exposed)/(rate of disease in unexposed)

IRR= (incidence rate in exposed)/(incidence rate unexposed)

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Odds ratio or exposure OR

[(E+,D+)/(E-,D+)]/[(E+,D-)/(E-,D-)

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Components of an Outbreak Investigation

1) Verify the _ and confirm the _
2) Define a _ and conduct _ _
3) Tabulate and orient _: _, _, and _
4) Take immediate _ _
5) Formulate and test _
6) Plan and execute _ _
7) Implement and evaluate _ _
8) Communicate _

Components of an Outbreak Investigation

1) Verify the diagnosis and confirm the outbreak
2) Define a case and conduct case finding
3) Tabulate and orient data: time, place, and person
4) Take immediate control measures
5) Formulate and test hypothesis
6) Plan and execute additional studies
7) Implement and evaluate control measures
8) Communicate findings

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Steps to determine if an outbreak is real

1) verify _
2) define a _
3) ID & count _
4) _ vs _
5) rule out other _

Steps to determine if an outbreak is real

1) verify diagnosis
2) define a case
3) ID & count cases
4) Observed vs expected
5) rule out other reasons

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Hypothesis generating vs. hypothesis testing

Hypothesis generating:

Attempt to identify most likely exposures

- Cases only, limited number

- Open-ended questions

Hypothesis testing:

Focus on most likely cause or causes
Include comparison group
Closed-ended question

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Attack rate= _

Eqt?

Attack rate= CI

(New cases)/(Population at risk)…. over time t

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Secondary attack rate

Secondary Attack Rate = P(D+|_)

Secondary attack rate

Secondary Attack Rate = P(D+|Contact with a known case)

Secondary Attack Rate = P(D+|Exposure to a known case)

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Describe common source point epidemic

Sharp slope w/ gradual downslope

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Describe Common Source Point with Secondary Transmission (Mixed)

Initial point source with subsequent person-to-person transmission

May have either:
a bimodal appearance Or
a prolonged downslope

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Describe Common Source Continuous Epidemic

Rise sharply, as with point source

Plateau reached and sustained

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Describe a propagative epidemic

Encompasses several generations of the agent

Begins with single case or small number of cases

Downslope related to exhaustion of susceptible hosts

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What outbreak?

Common Source Continuous

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What outbreak?

Common Source Point

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What outbreak?

Propagative

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What outbreak?

Common Source Intermittent

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Simple Structure of Four Study Designs

A) Pros Cohort

B) Retro Cohort

C) Case Control

D) Cross-sectional

Best use for cohort study (2)

short latent period

well-defined pop at risk

Best uses for case-control

Long latent period

unclear pop at risk

common exposure

best use cross-sectional

initial evaluation- Used to take out population that isnt at risk anymore

Study design: **Cross Sectional** Measure of frequency: Measure of association:

Study design: **Cross Sectional** Measure of frequency: **Prevalence** Measure of association: **Prevalance ratio**

Study design: **Case Control** Measure of frequency Measure of association

Study design: **Case Control** Measure of frequency: **None** Measure of association: **Odds ratio**

Study design: **Retrospective cohort** Measure of frequency: **Cumulative incidence** Measure of association other consideration

Study design: **Retrospective cohort** Measure of frequency: **Cumulative incidence** Measure of association: **Risk ratio** other consideration: **Use with minimal loss to follow-up**

Study design: **Retrospective cohort** Measure of frequency: **Incidence rate** Measure of association other consideration

Study design: **Retrospective cohort** Measure of frequency: **Incidence rate** Measure of association: **Incidence rate ratio** other consideration: **Use with loss to follow-up; recurrent disease**

Study design: **Prospective cohort** Measure of frequency: **Cumulative incidence** Measure of association: other consideration

Study design: **Prospective cohort** Measure of frequency: **Cumulative incidence** Measure of association: **Risk ratio** other consideration: **Use with minimal loss to follow-up**

Study design: **Prospective cohort** Measure of frequency: **Incidence rate** Measure of association other consideration

Study design: **Prospective cohort** Measure of frequency: **Incidence rate** Measure of association: **Incidence rate ratio** other consideration: **Use with loss to follow-up; recurrent disease**

Epi causal triad

Host Agent Environment

Epi causal triad: AGENT (3)

Infectivity; pathogenesis; virulence;

Infectivity ## Footnote The characteristic of the agent that reflects the ability to **\_**, **\_**, and\_**.**

Infectivity ## Footnote The characteristic of the agent that reflects the ability to **enter**, **survive**, and **multiply** i**n the host.**

Pathogenicity Property of an organism that determines the **\_** to which overt disease is **\_** in **\_**

Pathogenicity Property of an organism that determines the **extent** to which overt disease is **produced** in **an infected population**

Virulence: A measure of the **\_** caused by an organism

Virulence: A measure of the **severity of the disease** caused by an organism

Infectivity eqt

people infected/ people exposed

pathogenicity eqt

clinical cases/ people infected

virulence eqts

severe cases/ clinical cases severe cases/ people infected clinical cases/ people infected

incubation period

time between infection and clinical symptoms

Latent period

time between infection and infectious period

serial interval

time between clinical symptoms in 1\* and 2\*

what comes first, infectious period or clinical symptoms?

infectious period

Reproductive (reproduction) number (R) average number of **\_** per **I**

Reproductive (reproduction) number (R) average number of **successful transmissions** per **infectious person** Secondary cases/ primary cases

R: When will an epidemic stop?

So with R \< 1, the epidemic is not sustainable

When should R be at a maximum? R0: Basic reproductive number

If everyone is susceptible (s = 1), R should be at its maximum. R0 = average number of secondary cases caused by a single, typical person in a **completely susceptible population**

Rn : Net (effective) reproductive number If the infection is initiated in a population with \<100% susceptibility, the net R (Rn) will be less than **\_** Similarly, as the number of susceptible persons in a population is not stable (e.g. disease causes immunity), **\_**

Rn : Net (effective) reproductive number If the infection is initiated in a population with \<100% susceptibility, the net R (Rn) will be less than **R0** Similarly, as the number of susceptible persons in a population is not stable (e.g. disease causes immunity), **R will change over time**

Rn: Function of R0 and proportion susceptible eqt?

Rn =R0\*s Where s = proportion of the population that is susceptible to the infection

Herd immunity threshold (HIT) eqt If the population can attain a level of immunization (or immunity) \> HIT, what will happen?

HIT= 1–s =1–1/R0 HIT=(R0 –1)/R0 If the population can attain a level of immunization (or immunity) \> HIT, what will happen? **The epidemic should end**

Components of R0

R0 = pcD transmission probability (p); ``` contact rates (c); length of infectious period (D); ```

Rn = R0\_= pcD\_

Rn = R0s = pcDs transmission probability (p); ``` contact rates (c); length of infectious period (D); ``` proportion of susceptibles (s)

What does the relationship R = pcDs suggest about potential targets / mechanisms for control strategies?

Reduce transmission probability (p); early treatment Decrease contact rates (c); stay home!!! (quarantine) Reduce length of infectious period (D); treatment Reduce proportion of susceptibles (s): flu shots (immunization)

Cancer Clusters difficulties

Clusters sometimes result from confounders Difficult to establish a cause-and-effect relationship between disease and exposure extra Often fail to come to a satisfactory conclusion. Unable to confirm a geographical or temporal excess in the number of cases A cluster may be a collection of several diseases Establishing source of cluster very difficult

Cancer cluster Preliminary Evaluation: SIR

Standardized incidence ratio Number of observed/ expected Non-infectious disease